Touchdown the Development of Propulsion Controlled Aircraft at NASA Dryden

8/7/2019 Touchdown the Development of Propulsion Controlled Aircraft at NASA Dryden

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M ONOGRAPHS I N AEROSPACE H ISTORY # 1 6

by

Tom Tucker

Touchdown:

The Developmentof Propulsion

Controlled

Aircraft at

NASA Dryden


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Touchdown: The Development of

Propulsion Controlled Aircraft

at NASA Dryden

byTom Tucker

NASA History OfficeOffice of Policy and Plans

NASA Headquarters

Washington, DC 20546

Monographs in

Aerospace History

Number 16

1999


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Table of Contents

Foreword............................................................................................................. iv

Preface ................................................................................................................. v

The Development of Propulsion Controlled Aircraft at NASA Dryden.............. 1

Appendices

Appendix A: Aircraft Accident Report, United Airlines Flight 232 ............ 36

Appendix B: Flight Simulator Studies ........................................................ 38

Appendix C: National Transportation Safety Board Recommendation ...... 39

Appendix D: Guest Pilot Comments on . . . F-15........................................ 40

Appendix E: PCA System Landing in MD-11 Aircraft ............................... 46

Appendix F: Summary of Guest Pilot Comments about . . . MD-11 .......... 47

Appendix G: Awards and Honors [for the PCA Team] ............................... 50

Index .................................................................................................................. 51

About the Author ............................................................................................... 54


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Foreword

This monograph relates the important history of the Propulsion Controlled

Aircraft project at NASAs Dryden Flight Research Center. Spurred by a

number of airplane crashes caused by the loss of hydraulic flight controls, a

NASA-industry team lead by Frank W. Burcham and C. Gordon Fullerton

developed a way to land an aircraft safely using only engine thrust to control theairplane.

In spite of initial skepticism, the team discovered that, by manually manipulat-

ing an airplanes thrust, there was adequate control for extended up-and-away

flight. However, there was not adequate control precision for safe runway

landings because of the small control forces, slow response, and difficulty in

damping the airplane phugoid and Dutch roll oscillations. The team therefore

conceived, developed, and tested the first computerized Propulsion Controlled

Aircraft (PCA) system. The PCA system takes pilot commands, uses feedback

from airplane measurements, and computes commands for the thrust of each

engine, yielding much more precise control. Pitch rate and velocity feedbackdamp the phugoid oscillation, while yaw rate feedback damps the Dutch roll

motion.

The team tested the PCA system in simulators and conducted flight research in

F-15 and MD-11 airplanes. Later, they developed less sophisticated variants of

PCA called PCA Lite and PCA Ultralite to make the system cheaper and there-

fore more attractive to industry. This monograph tells the PCA story in a non-

technical way with emphasis on the human aspects of the engineering and

flight-research effort. It thereby supplements the extensive technical literature

on PCA and makes the development of this technology accessible to a wide

audience. I commend this brief account to anyone interested in the progress of

aviation technology.

Kevin L. Petersen

Director, Dryden Flight Research Center

18 February 1999


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Preface

Many histories of invention look back over decades and even centuries to tell theirtale. But another perspective comes from the middle of the process, when theoutcome is uncertain, when questions remain, when the invention and developmentprocess remain a hazard of fortune. It is a rewarding experience to view develop-ing technology from this angle. The story of the invention and development of

Propulsion Controlled Aircraft at NASA Dryden Flight Research Center made thispoint again and again to me in the summer of 1998 as I researched the inventionwithin several hundred yards of where only several years before, the first jumbo jetlumbered in for a safe landing using the new technology.

I owe a great debt to the many individuals, programs, and organizations whichenabled me to write this history. First, I am grateful to the NASA - ASEE SummerFaculty Fellowship Program which brought me to NASA Dryden Flight ResearchCenter out in the Mojave Desert and supplied me with every kind of support neededfor research and writing. At Dryden Center, Don Black and Kristie Carlson providedmuch courtesy and good advice. At the Stanford University Department of Aeronau-tics and Astronautics, Melinda Francis Gratteau, Program Administrator, andMichael Tauber, Co-director of the Program, aided me invaluably with their help,consideration, and provision of opportunities. The participatory programs theyoffered to me and other NASA ASEE fellows at the NASA Ames Research Centerhelped me in thinking about and clarifying this invention history project.

Many people inside and outside NASA gave generously of their time and expertisein interviews and correspondence. These included: Russ Barber, Bob Baron, JohnBull, Bill Burcham, John Burken, Joe Conley, Bill Dana, Dwain Deets, MichaelDornheim, John Feather, Dennis Fitch, Gordon Fullerton, Glenn Gilyard, AlHaynes, Tom Imrich, Jeff Kahler, Yvonne Kellogg, John Lauber, Jeannette Le,Trindel Maine, John Miller, Terry Neighbor, Drew Pappas, Dana Purifoy, Joel Sitz,Walt Smith, Jim Smolka, Jim Stewart, Ken Szalai, Jim Urness, Tom Wolf, and BobYeager.

Readers of drafts along the way offered many valuable comments. I especiallythank: Bill Burcham, Roger Launius, Trindel Maine, and John Miller. I am gratefulto Dennis Ragsdale of the NASA Dryden Library for tracking down my numerousresearch requests. Steven Lighthill and the NASA Dryden Graphics Department aswell as the NASA Dryden Photo Lab went above and beyond the call of duty ingiving this project the benefit of their talents. Camilla McArthur deserves recogni-

tion for her expert work arranging for the printing of the monograph through theGovernment Printing Office.

Last and most, I owe a debt to Dill Hunley, chief editor, advisor, facilitator, andfriend who throughout the process made this history much better than it could havebeen through my efforts alone.

Tom TuckerSpindale, NC12 April 1999


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Touchdown:

The

Development

of Propulsion

Controlled

Aircraft at

NASA

Dryden

At 30,000 feet altitude flying to St. Louison a business trip, Bill Burcham, thenChief Propulsion Engineer at NASAsDryden Flight Research Center, had anidea that would change his life. It was alate summer day in 1989. Burchampushed aside his well-thumbed copy of

the trade journalAviation Week & SpaceTechnology. As the peaceful routine of thecommercial flight went on, he began todraw. He began a sketch on the back of aTWA cocktail napkin.

Burcham, a thirty-three year veteran inaeronautics at NASA, is well-known tohis colleagues as a man whose emotionseven in emergency never modulatebeyond matter-of-fact. So there were noEureka shouts. There was only his pen

dancing over paper.

The spark that started him thinking wasthe latest in a series of articles appearingthat summer about a major jet crash.1 On19 July 1989, a widebody jet had experi-enced disaster during a routine flight overIowa farmlands. The rear engine hadblown out. The loss of this engines thrust

was not central to the mayhem thatfollowed. In fact, the two other enginesslung under the wings remained sufficientfor somewhat regular flight. But thehydraulic system had vanished. Thehydraulics operate all the controls that apilot uses to control flight. The airplanehad three hydraulic systems, any two ofthem capable of providing almost normalcontrol, and any one capable of providinga safe landing, but the shrapnel from theexplosion had taken out all three. Sud-

denly, the control wheel was dead in thepilots hand.

Figure 1. Bill

Burchams PCAnapkin, showing

the diagram ofDrydens Propul-

sion ControlledAircraft project. Inthe diagram,

DEFCS stands forDigital Electronic

Flight ControlSystem, a comput-erized system that

provides digitalflight controls;

HIDEC stands forHighly Integrated

Digital Electronic

Control. (NASAphoto EC94-42805-

1 by DennisTaylor).

1See Frank W. Burcham, Cleared for Landing,Air & Space(April/May 1995): 20-21.

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would have been that if you tried to landan airplane on a runway with this technol-ogy, you would end up with a smokinghole in the ground.

* * *

Out in the Mojave Desert 70 milesnortheast of Los Angeles are the plainoffices, metal shacks, and hangars thatcomprise the NASA Dryden FlightResearch Center on Edwards Air ForceBase. The ancient dry lakebed gleams inthe afternoon sun as if it were a fantasticillustration for a science fiction paper-

back. But even more paradoxical are thelabs and offices where on battered federaldesks dating back two generations,concepts for use in the aircraft of the nextmillennium are born and developed.Despite NASAs charter commitment tocommercial air safety innovation, it wasalso, by many standards, a strange site forBurchams idea.5

The napkin scheme did not initially cometo life with the dignity of a project with abudget, but for months Burcham pushed it

along in an hour snatched at the end of aweek. Or after a days flight, he wouldcall the research pilot and in his affable,low-key manner inquire, Gotta hundredpounds of extra gas; could you try thisbackup card test point? The researchershave names for this type of investiga-

tionthey call it bootlegging orpiggybacking or in the noise (anengineers term for experimental effortsso minimal they can be neglected). Nodramatic leaps greeted this effort, whichwas to become for Burcham somethingnear a quest. The path was evolutionrather than revolution.

Stewart and Burcham had been exploringa new technology known as HIDEC,Highly Integrated Digital ElectronicControl, an attempt to optimize engineperformance to match the flight condi-tions of the aircraft by integrating engineand flight control systems. A follow-onactivity involved doing on-board diagnos-tics when an airplane was damaged andthen reconfiguring what remained func-tional to fly the airplane.6

5Although NASAs Dryden Flight Research Center and its predecessor organizations have an illustrious history of flight

research on a wide variety of aircraft, other NASA centers have traditionally been more closely associated with transport

technology.

6Despite the temptation to trace connections between HIDEC and Burchams new project for landing aircraft with

engine controlwhich came to be called Propulsion Controlled Aircraft (see below in narrative)and to view the earlier

project as a conceptual starting point for the later one, these are quite distinct programs. In editorial notes to this text,

Dryden engineer Trindel Maine cautioned, HIDEC really wasnt primarily a reconfiguration program, though at least

one reconfiguration program was flown under its auspices. Primarily it was a series of experiments designed to discover

and demonstrate the benefits of going to computer-controlled engines. This included a greater ability to recognize engine

problems, change engine setting depending on the situation, and cut out excess operating margins.

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Figure 4. Diagram of a Dutch roll.

We had already looked at engines,recalls Stewart; that is one thing all theseplanes have in common.7 It was a glancemerely, a preliminary study, no proof. Butthe engineers had already looked intoreconfiguration enough to speculate that ifmore than one control surface did not

function, the airplane was in trouble. Tolose them all and depend on engine thrustalone would be, in effect, the ultimatereconfiguration. In the pantheon of bad-case scenarios, this was the worst.

Passengers on a commercial flight mayinstinctively sense that destiny is in thecontrol of the big engines, the big airframe.But the most crucial parts are the narrowmetal strips: the ailerons on the back ofthe wings, the rudder, and the elevators

on the back of the tail fins that controlflightpath. These strips also dominatecertain unbalanced motions no pilotwants unleashed, motions known as thephugoid oscillation and the Dutch rolloscillation.

You experience phugoid oscillations inalmost any air flight. They probablymake an appearance as no more thanslight nibbles in a smooth passage,arising so gradually that normally thepilot touches the wheel and kills theoscillation without thinking about it.

The phugoid is a pitching motion inwhich kinetic and potential energy (speedand altitude) are traded. Each cycle of theoscillation typically lasts about 60seconds and may continue for manyminutes. As the airplanes nose pitches

to the highest point, speed slows. As thenose drops back toward the middle of thecycle, speed increases. The experienceresembles a sort of eerie slow-motionroller coaster ride. Its effect on landingscan be fatal if the motion continuesuncontrolled near the ground.

The second oscillation is known as theDutch roll (named for the motion of an iceskater). According to one NASA researchpilot, an airplane in the Dutch roll moderesembles a snake slithering.8 Obvi-ously, this is not a desirable way to traveloff the ground. This complex oscillationcombines several factors including yaw,roll, dihedral effect, lift, and drag. In a

7James Stewart, interview with author, 10 June 1998.

8Dana Purifoy, interview with author, 2 July 1998.

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Figure 5. An early

acronym and alsoa sample of Bill

Burchamsviewgraph

expertise

Dutch roll, the airplanes nose typicallyrotates through about three degrees.When an airplane tries to find the runway,there is only about one degree of marginfor safe runway touchdowns.9

Although concern with these mysterious

oscillations lay on the horizon beforeBurchams technology, the project had aclear, specific goalto land a jumbo jetusing engine thrust alone. None of the in-between steps were well defined andsome would not, as it turned out, resolvethemselves for years. Any proposedchange to passenger aircraft requiresendless refining tests, proof upon proof tocheck the vast web of real flight possibil-ity. The Federal Aviation Administration(FAA), the National Transportation Safety

Board (NTSB), the manufacturer, theairlines, and various associations and

advisory groups are all part of the mesh.But the unknowns stretched beyondregular procedures. We had to ask basicquestions, recalls Jim Stewart. Can youcontrol the airplane [this way]? And somehere were saying no.10

Burcham had already devised an acronymfor the project. The typical NASA projectgenerates several acronyms in its lifetime.To outsiders, the engineers who coin thesenames may seem like techies taking theirrevenge on the English language. Theacronyms are born and diefew of themever survive as standard usage, and theysometimes change on the same projectfrom report to report. You need ascorecard to read these reports, continu-ally referring to the inevitable Nomen-

clature section appearing on page oneright beneath the Abstract. Along the

9See Donna Gerren, Design, Analysis, and Control of Large Transport Aircraft utilizing Engine Thrust as a Backup

System for the Primary Flight Controls (unpublished thesis, University of Kansas, Feb. 1993): 20-22. This thesis was

later published as NASA CR-186035 in October of 1995.

10Stewart interview.

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Figure 6. TheDryden F-15

simulator cockpit.

way the project was known as PROTECT(PROpulsive Techniques for EmergencyConTrol), POC (Propulsion Only Con-trol), and PROFAC, an acronym thattoday causes all concerned to scratch theirheads when asked to explain its forgottenorigin. Marketing may be the true main-

spring behind these verbalizations. A goodacronym resonates. If you dont have agood acronym, offers one engineer,youre dead in the water.11 The ultimateacronym, coined by industry, turned out tobe PCA, Propulsion Controlled Aircraft.

The first step for PCA was to see if a pilotcould alter the course of the airplanesimply by working the throttles. To test

this, Burcham went to veteran simulationsengineer Tom Wolf. Can you lock downall the flight controls on a sim [simula-tion]? he asked.

The next morning, Wolf had the simready. He had altered the F-15 sim, amodel of a high performance fighter

airplane that he and Burcham used as atestbed for HIDEC projects. Burcham, askilled amateur pilot, climbed in thecockpit. First, he tried the lateral move-ment. Could he turn the F-15? I foundthat by advancing one throttle and retard-ing the other, recalls Burcham, the F-15

rolled nicely, even though the engines areclose together.

Next, he pushed both throttles up a bit.When he did, the airplane nosed upslightly. If he cut both throttles back, thenose dipped. He had demonstrated somelongitudinal control. In the excitement, allin a lunch hour away from his primaryproject, he moved on to the next step, the

simulated landing itself. Unfortunately,his exhilarating video screen journeycame to an end when he crashed short ofthe imaginary runway.

Burcham continued step-by-step. He wasdoing what Denny Fitch had done onFlight 232. He called it Throttles Only

11John Burken, interview with author, 9 June 1998.

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Control (TOC).12 It was a necessary step,not a destination. But with repeatedpractice, he managed to use TOC to landthe F-15 in the simulation. There seemedto be enough brute force there, he said,that I felt with a computer providingsome finesse, safe landings would be

possible.13

* * *

Glenn Gilyard is a 55-year-old seniorDryden controls engineer who specializesin computer-assisted controls. A large manwhose eyes gleam with elfin humor, herecalls his first encounter with PCA.Kevin Petersen, Chief of the VehicleTechnology Branch in the Research

Engineering Division, approached himone afternoon in 1990. Despite theskepticism at the Center, Petersen wasintrigued by PCA and hesitantly askedGilyard if he would put some time intothe project.

I jumped on it right off the bat, saysGilyard, This appearedfeasible.

Gilyard looked at the solution as anautopilot function. He had worked oninnovative solutions for the auto-throttleof the YF-12. What if he used the pilotscontrol stick to command direction? Theinput would go through the flight com-puter, which would also receive sensorfeedback from the airplane and use it tocalculate and move the throttles.

Where would they get the sim airplane tomake the control tests? Although the F-15simulation had already been used, in the

corner of the lab rested another sim froman abandoned projecta four-engine

transport, the Boeing 720. There was not areal Boeing 720 waiting outside on theEdwards base runway to take investiga-tion to the next level. Rather, it was theonly transport simulation available.

Gilyards eyes gleam with mischief when

he explains why the sim but no airplanewas available. Once Dryden did employ areal Boeing 720 for use in experiments.The FAA had committed a significantbudget and many technicians to com-pound a jet fuel with a new additiveintended to prevent airplanes fromburning on impact. It was a wonderfulidea. It had passed the reviews, thesimulations, the small-scale demolitionrehearsals. But the real flight was differ-ent. Later, investigation would reveal the

unforeseen factor, a wing cutter slicingthrough an engine on impact. The airplaneerupted in a giant fireball and burned foran hour.

The unhappy project had flown under theacronym CID, Controlled Impact Demon-stration. Gilyard smiles, recalling thatwags on the base to this day explained theacronym as Crash In Desert.

It burned like a blowtorch, recallsGilyard.14

* * *

Now Burcham had an informal teamassembled to work on PCA control lawsincluding two newcomers, Jeanette Le,just graduated from UCLA, who wouldfunction as the sim engineer, and JoeConley, fresh out of the engineeringprogram at the University of Illinois and

the NASA coop program, who would beresponsible for the analytics. Burchams

12The acronym TOC is important to this history. It refers to the pilot manually operating the engine throttles to provide

flight control. The acronym later adopted, PCA (Propulsion Controlled Aircraft), refers to augmented controls the project

developed to help the airplane land.

13Burcham, Cleared for Landing, 20.

14Last section based on Glenn Gilyard, interview with author, 16 June 1998.

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project had advanced beyond the fourcorners of his desk to become a trainingground for two new-hires with a thrift-shop choice for its testbed.

Late in January of 1990, Gilyard sketchedout the control laws. More than anyone

anticipated, the first effort looked verygood. Le brought up what had early-onbeen a more-than-adequate 720 sim andmodeled it for flight using throttles forflight-path control and other multiplescenarios. Within a week, these engineerswere flying the PCA system in the simlab.

No pilots involved at first, winksGilyard, no sense in embarrassingourselves, huh? Typically it takes months

and months if not years to get results.Normally, you start at your desk; youmake a mathematical representation ormodel of the aircraft. Then you do thecontrol law design at your desk. What wedid was the exception to the rule. Wejumped right into the sim.15

A simulation is a software model of anairplane. The model includes a maze ofsubsystems, the propulsion system, thecontrol system, an aerodynamic model, anactuation model, a model typically of aspecific airport and actual runway, modelsof weather, wind, turbulence, gusts. Ineffect, when you stepped into the ply-wood cockpit of the Dryden 720 sim, youentered an elaborate video game, anarrangement that might answer anynumber of speculative questions aboutflight but that at the same time entailednone of the risks of real flight.

The 720 sim was rough. It was a plywoodbox; it had only two throttles so that thesim had to tie two software enginestogether on the left and two on the right.

The video screen offered a tiny rectangle.The mathematics of its models had beenderived for another project whose focuswas crashing, instead of not-crashing. Yetthe more sims Burcham saw, the morecertain he became that in some manage-able way, thrust would do to land an

airplane.16

During these quickie formulations,another issue arose. It was not part of thepropulsion control modeling. But it waspart of any safe landing in a catastrophicscenario. The speed of the aircraft withoutnormal flight controls is mostly lockedinto the speed flown before control waslost. An aircraft has what is called its trimairspeed, an inherent speed the airplaneattempts to maintain. Speed is only

peripherally affected by changing thrust.To an outsider, it might seem that if youwant your car, for instance, to slow down,you take your foot off the gas pedal. Butin the PCA mode, if you cut back on thethrottle, you do not decrease speedyoupitch the nose down. Correspondingly, ifyou bring up the throttle, you pitch thenose up. The increases and decreases inangle of attack cause drag which margin-ally affects speed, but you face a problem:if you are flying at altitude at 280 knotsand experience catastrophic loss of yournormal controls, even when you engagePCA, you still fly at somethingunnervingly close to 280 knots. How doyou slow down to perhaps the 170 knotsneeded for a safe landing? Here was anissue to address. But as Gilyard, the oldcontrol-law warrior, noted: his assignmentat this point was done, and the flightdemonstration was for othersit was, ashe phrased it, another set of realities.17

For the moment, the problem of trimspeed could be postponed. Burcham hadsome promising results, and he needed

15Gilyard interview.

16Jeanette Le, interview with author, 24 June 1998.

17Gilyard interview.

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Figure 7. Dryden

Director Ken

Szalais note to BillBurcham.

every bit of confidence he could get.There were many naysayers on the topicof PCA, and the roughest criticism camefrom the nearest hallways. This is justplain stupid, snorted one fellow engineer.Hare-brained! echoed another aeronau-tical designer. A Dryden expert warned

him, You are defying the laws of phys-ics! Skepticism was voiced from alllevels, low and high. The PlanningCouncil at Dryden did not offer funds.By the time you had brought it up to tenpeople, recalls Jim Stewart who sharedthe early advocacy, you almost hated tobring it up. Burchams logbook hasentries for many PCA briefings thatwinter which end with the notation nointerest.18

Why were there so many doubters?Perhaps one of the answers was cultural.In this realm of specialized research, therewas a propulsion culture and a separateflight control culture. PCA was a hybridof both that pleased traditionalists inneither. And another factor surfaces too:

the whole concept of PCA was, in a largeway, unsettling. An engineer now sympa-thetic who prides himself on openness tonew ideas recalls that at first he did notthink the technology would work, PCAwasnt intuitively obvious. The problemhinged on this, his eyebrows widen foremphasis, It was novel.19

Early in the spring, Burcham received abrief note from Ken Szalai, Director at

18Frank W. Burcham, unpublished log books; Stewart interview. The Jim Stewart interview with the author was one of

the more extensive sources on early skepticism about PCA.

19Tom Wolfe, interview with author 4 Aug. 1998.

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NASA Dryden. Although it was informal,casually scrawled by hand, the notearrived as a real trumpet blast. I want todevelop the propulsion-enhanced flightcontrol work as a NASA-led R&D[Research and Development] program,with strong in-house technical and

technology leadership, he announced.20

Szalai did not offer him a budget orpeople to stack against the project, but atthis stage, what he offered may have beenmore essential. Szalai had received amessage from NASA Headquarters inWashington, D.C. There was concern atHeadquarters that PCA might excite theregulatory agencies before it had beenfully explored and create problems for theaircraft manufacturers. The advice I gotfrom Headquarters, recalls Szalai, was:

Wed prefer you not actually work onthis at allwhich was a stunning blow tome.21 Szalai chose to act as buffer ratherthan a messenger. Burcham recalls, Myboss forgot to tell me this until severalyears later.22

Burcham flew most of the Boeing 720sims. What was the next step? Burchamneeded to test the concept in actual flight.Thus, he needed a real airplane and a realpilot.

In March of 1990, Burcham paid a visit tothe pilots office. He ambled over to apilot at his desk. He asked, What do youthink about using engine thrust for flightcontrol? Would you like to take a look?How about flying a rough sim? The pilotwas Gordon Fullerton.

Fullerton was in his early fifties then, agraceful, athletic man with pale blue eyes

that could gleam with humor. His facewas burnished, even wizened perhapsfrom thousands of hours of flying in thefierce glare of the desert. Everyone on thebase called him Gordo, this ex-astronautand test pilot whose skills were the stuffof legend.

Fullertons eyes glittered at Burchamsquestions. Yes, he was definitely inter-ested. Here was the man who had broughtthe STS 51F Space Shuttle down atDryden willing to try to land a crippledcommercial lineror at least the simula-tion of one.

In an instant in the hallways at Dryden,PCA gained credibility.

It was some combination of curiosity andthe challenge that hooked Fullerton. Hefollowed Burcham to the plywood cock-pit. Burcham mentioned that he himself,after some practice, had accomplished asuccessful landing using the throttles forcontrol. How would you like to try? heasked.23

When Fullerton tried this unusual system,he entered a new realm. Where normalflight controls had done his bidding in aneyeblink, even in simulation the biglethargic engines might take what seemedlike an eternity to respond. It was wait-and-see flying, a sort of dismayingprocess of anticipation, especially becausethe real-world situation would be one ofdesperation. The pilot commanded; thepilot waited. Later, one NASA test pilotreferred to this type of flying as herdinga cow across the sky.24

20Kenneth J. Szalai, unpublished note, 14 Mar. 1990.

21Kenneth J. Szalai, interview with Dill Hunley, July 1998.

22Burcham, Cleared for Landing, 21

23Burcham interview, 12 Aug. 1998.

24Purifoy interview.

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To a nonpilot, the comparison would bedriving on the freeway and having to turnthe steering wheel nearly half a minute inadvance of the vehicles response. Aphugoid cycle, for instance, lasts about 60seconds and the thrust input to damp itmust be given more than 20 seconds

before there will be a perceptible indica-tion that the input has had an effect. If thepilot gives a command, then observes noreaction, he may repeat the command andovercorrect with damaging effect. With-out flight controls, if the airplane nosesup, threatening to stall, the pilot will pushhis throttles forward, the reverse of thethrust input needed. In these last-resortcircumstances, Joe Conley points out,pilots will revert to natural instincts andnatural flying instincts will kill you.25

Burchams insight, which dated back tothe sketch on the napkin, was that while apilot would find it impossible to stop aphugoid with less than a 50/50 chance ofeven nudging the thrust in the right half ofthe oscillation, if a computer could helpif it could receive responses from motionsensors 40 times per second and react toeach with a tiny correcting, nearly imper-ceptible nudge of the throttletheairplane could be controlled.

Flying TOC (Throttles-Only Control) wastough. But after five or six tries at thesim, Fullerton mastered the task. Histechnical curiosity may have weighed inas one factor, but the larger factor was thechallenge. Ego in abundance is requiredof flyers in his occupation. Test andresearch pilots needed it to function,given the risks involved. The risks werereal. If you look up at any street sign inthe numerous roads intersecting around

the Edwards runways, you see the namesof pilots who have gone down in fireballson the desert just beyond.

Fullerton had followed the Sioux Cityincident as closely as Burcham. As aresearch pilot who daily faced risk and the

potential for deadly surprise, he admiredwhat the pilots at Sioux City had accom-plished. What you guys did blew meaway, he later told Dennis Fitch, theairline check pilot who had come forwardthat day from the passenger section towork the throttles.26 In these early stages,Fullerton brought an additional front tothe attack on the problem, one a bitignored since then. He sought to developa set of practical guidelines to help pilotswhose airplanes lost some or all flight

control surfaces.27

In addition to his willingness to evaluatesim flights, Fullerton made anothercontribution. He had noticed that someguest simulation pilots had problems evenafter the PCA was engaged. One fightertest pilot, remembers a Dryden controlsengineer, never did get the hang of it.28

At first glance, the stick had seemed themost efficient way to introduce andcontrol PCA. But in a catastrophe, the

pilot might expect the stick to respondimmediately as in normal flight. Fullertonsuggested putting the controls inthumbwheels, the hardware typically usedin operating autopilots. Two thumbwheelswere added to the panel, one for dialing inlateral commands, the other for longitudi-nal commands. Tests with more guestpilots confirmed the decision. Thethumbwheels, says Jim Stewart, put itin the comfort zone.29

25Joseph Conley, telephone interview with author from NASA Ames, 19 June 1998.

26Dennis Fitch, telephone interview with author, 15 July 1998.

27Gordon Fullerton, interview with author, 7 July 1998.

28Burken interview.


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Another significant breakthrough camefrom Joe Conley. As he worked throughlanding data in analytics, he stepped backmentally and asked himself if there weresome way to make his outcomes morepredictable. Burcham had conjecturedabout using the ILS (Instrument Landing

System)a radio-beamed trackingsystem that helps guide actual airplanesonto the runway in bad weather. What ifthe inputs from ILS were added to theinputs PCA used? Conley designed asimple ILS and added it to the PCA sim. Itwas a deft move. In terms of the sim, thescheme was merely a pleasant improve-ment, but in a year, in terms of realairplanes coming down onto the runway,it played an important role.

Some PCA skeptics viewed Sioux City asa once-only instance. Why bother? theyexplained, because it will never happenagain. Burcham and Fullerton did someresearch looking for other airplaneaccidents that could be traced to losthydraulic controls. At first, the naysayerswere confirmednothing showed up.Then one afternoon while traveling, JimStewart gave a talk about PCA. After-wards, an Air Force man came up to himout of the audience. I have to talk to

you, he said.30

In 1975, an incident happened in Vietnamto a USAF C-5 transport evacuatingorphans from Saigon. When a bulkheadfailed in the aft fuselage, all hydraulics tothe tail were lost. The pilots had flightcontrols for roll but none for pitch. Theytried using the throttle and found that itprovided some pitch control, but were

unable to control a phugoid on approachfor emergency landing. The phugoidcaused the aircraft to crash-land into a ricepaddy. Of 314 passengers, 138 died but176 survived.

In the months that followed, the Dryden

searchers discovered other incidents. In1985, a Japan Airlines flight suffered totalhydraulic loss. Out of control, the airplaneflew for 30 minutes before hitting amountain, killing 520 people. The sameyear as the Sioux City crash, a Navyfighter flying over Jasper County, Indiana,lost hydraulic controls, and when theaircraft rolled off uncontrollably to theright at an angle of 90 degrees, the pilotejected. Another crew on a commercialflight near San Diego found the airplane

about to stall in an uncontrollable pitch-upwhen they used throttle controls, changedpitch by thrust modulation, and landedsafely. A 1974 flight departing Paris wasless fortunate. The airliner lost some flightcontrols, diving into the ground at highspeed. All 346 aboard perished.

It was grim arithmetic but was part of thefactoring needed to convince an industryand its regulators to look seriously atPCA. As other accidents came to light, the

Dryden researchers assembled a list ofrelatively recent incidents involving morethan 1,100 fatalities.31

* * *

One of the guest pilots in the spring of1991 was Al Haynes, captain of the SiouxCity Flight 232. During the year after thecrash, he began to give an inspirational


31Cf. Frank W. Burcham et al.,Development and Flight Evaluation of an Emergency Digital Flight Control System

Using Only Engine Thrust on an F-15 Airplane(Edwards, CA: NASA TP 3627, 1996): 2-5, and Military Airlift Com-

mand History Office,Anything, Anywhere, Anytime: An Illustrated History of the Military Airlift Command, 1941-1991

(Scott Air Force Base, IL: HQ MAC, 1991), pp. 152-153.

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Figure 8. Al Haynes

in the Boeing 720simulator with (left

to right) GordonFullerton, Bill

Burcham, and JimStewart. (NASAphoto EC91-316-2

by Bob Brown).

speech around the country regardingcockpit resource management and emer-gency preparedness. He came to Drydenand spoke to an overflow audience.32

Afterwards Burcham and Fullerton tookhim to see the 720 sim, but when theyinvited him to fly it, he turned them

down.

Here was unexpected resistance. Thispilot had been rock-steady during hisordeal. In audiotapes of his remarks to theSioux Gateway control tower, there wasnot a crack in his voice as Haynes an-nounced as casually as if he were talkingabout weekend recreation plans, Werenot gonna make the runway, fellas.33

But this was different. He hesitated;

perhaps his eyes moistened.

I dont think I want to fly the simula-tion.

Why? asked Fullerton.

I dont know . . . to get back in a cockpitfaced with the same situation.

He stared a moment at the dim contrap-tion. But he did get in; he flew the simlater that afternoon. He punched the PCAbutton, approached the runway; PCAeased him to glideslope, and the grayrunway on the video screen came closer.On his first effort he was able to put theplane safely on the ground.

Al Haynes was pleased.34

32Al Haynes, interview by telephone with author, 16 June 1998.

33Al Haynes, from video accompanying speech, The Crash of Flgt. 232, 24 May 1991.

34Most of the Haynes and simulator story come from the Gordon Fullerton interview.

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* * *

Burchams idea wasbig. It was big in theunexpected ways it kicked in sometimesmore strongly than the engineers had everpredicted. Bill was the first impetusbehind the project, but PCA was much

bigger than any one individual, and teamswould form and reform, members drop-ping in and out, one person making somesignificant, defining contribution, thenanother. At the NASA center best knownfor supersonics, this subsonic idea lum-bered along with the speed of a transport.It survived, moving through an institution,through units and sub-units, a bit of astealth project because it had no budget tobe shot down, moving through maturetechnology, moving through an

engineers off-time on Saturday after-noon, through carpool debates, reviews,briefings. And PCA was about toreconfigure with another unit that wouldhelp it survive, the U.S. Air Force.

Burcham was looking for funds. He couldnot buy an airplane, but he needed tobuy a feasibility study, to look at how toprove the PCA concept, how toreconfigure a real airplane with thistechnology. The Air Forces Terry Neigh-

bor from Wright-Patterson Air ForceBase, who headed a group investigatingcontrols integration, had listened toBurcham pitch PCA to another Air Forceunit, which ultimately expressed lack ofinterest. Neighbor did find PCA interest-ing. He recalls it as another dimension ofsomething we were doing. Neighborwent back to his office, got his hands onsome managerial discretionary funds,initially $100,000, which in the scheme ofmore visible projects was pocket change,but which for PCA was a vital infusion,

the funds needed for a feasibility study onthe projects first real airplane testbed, anF-15.35

NASA Dryden had an F-15 in the hangarat Edwards. The F-15 is a high-perfor-mance fighter airplane from McDonnell

Douglas Aerospace.36

What attractedBurcham was that this Dryden F-15 hadtwo computer systems, a digital flightcontrol computer, FCC, and digitalelectronic engine controls, DEEC. Thesetwo systems can talk to each other, andboth are programmable. Earlier projectsmost recently, HIDEChad alreadyloaded Drydens F-15 with expensivetesting instrumentation. Despite theseattractions, among all the airplanes in theworld if the researchers had been given a

choice, the F-15 would have rankedamong the last.

The problem was the engines. They weretwo big, powerful turbofans relegated tothe rear of the airframe. A mere 12 inchesseparated the two brutes, and if PCAtechnology depended on differential thrustbetween the right and left engines, howwould the F-15 respond? Some roughsims had looked encouraging, but simswere sims, and the robust power of flight

control surfaces might have masked theeffects of the closely spaced engines.

The study was contracted to McDonnellDouglas Aerospace in St. Louis, Missouri.New faces now appeared on the team.McDonnells Jim Urnes became projectmanager for the task and Ed Wells wasdesign and flight test engineer. Now tripsto simulators took Burcham and hiscolleagues to the spectacular F-15 simula-tion in St. Louis. It was a real F-15cockpit with real F-15 controls, and

35Terry Neighbor, interview by telephone with author, 4 Aug. 1998.

36Today, the companies mentioned in this history are all part of Boeing. But in these pages, they will be designated as

they were then separately known for most of the duration of the PCA work. They included McDonnell Douglas Aero-

space in St. Louis, which did PCA studies for the F-15; McDonnell Douglas Aerospace Long Beach, which did PCA

studies for the MD-11; and Douglas Aircraft Company operating the MD-11 out of Long Beach and testing in Yuma.

Boeing was a separate and independent company headquartered in Seattle.

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dramatic scenery wrap-around on theinside of a 40-foot dome. If Burcham hadan hour remaining at the end of a daydevoted to the big HIDEC project, he rana PCA test.

Safety features designed into the sim

were the ones to be designed into the realairplane. All modifications were softwareoneswith one exception, the addition ofa cockpit controller for PCA. The hydrau-lics were never turned off. The pilot usedthe emergency mode of the mechanicalflight control system, which did not havethe flight control computers automaticallydriving the control surfaces. At theslightest touch to stick or rudder pedals,the pilot could engage the normal flightcontrol surfaces.

Drydens Tom Wolf introduced manymodifications to the Dryden F-15 sim toaccount for the new F-15 configuration.Ed Wells, the St. Louis F-15 specialist,added these control laws to theMcDonnell sim and customized the 720version of the flight control laws for theF-15.

Hardware arose as an issue. Fullerton hadvoted for thumbwheels as the controllersof choice, but McDonnell decided thequestion needed systematic review. Andthe thumbwheels posed a problem:McDonnell had a thumbwheel panel froman F-4 Control Configured Vehicle (CCV)

program that was qualified only for labuse. The researchers did not have a flight-qualified unit to install in a real airplane.Jury-rigging knobs for a sim was onething but installing hardware not certifiedfor flight was another. Our shoestringprogram did not have the funding fordesigning or building new ones, remem-bers Burcham. McDonnell framed fouroptions for the study. These included thecentral control stick, a ministick spring-loaded and moved by force, another

spring-loaded ministick moved by de-grees, and the F-4 CCV thumbwheels.Each option had negatives, and a series ofguest pilots flying the sim again deci-sively confirmed the wisdom of thethumbwheels.37

Where to get the flight hardware? At thispoint, the Air Force came to the rescue,

Figure 9. GordonFullerton and the

two brutes(engines) in the F-

15 after he hadlanded the aircraftusing only engine

power for controlon 21 April 1993.

(NASA photo

EC93-41034-3 byLarry Sammons).

37Burcham interview, 17 June 1998; Edward Wells and James Urnes,Design and Flight Test of the Propulsion Con-

trolled Aircraft (PCA) Flight Control System on the NASA F-15 Test Aircraft(Edwards, CA: NASA CR 186028, Feb.

1994): 9-11.

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and Major Bob Yeager, who had joinedthe PCA team, tracked down thethumbwheels still in an F-4 CCV restingin a flight museum in Dayton, Ohio. Hetalked the museum into loaning thethumbwheel panel; herded the curioustransaction through stacks of paper

regulations; and for the life of the project,the F-15 sported flight-qualifiedthumbwheels.

It was clear from the beginning that theteam would need to perform actual flighttests of PCA. Some engineers say thatflight tests are not needed when a goodsimulation will suffice. But PCA itselfwas so new, so different, that manyquestions arose. The test to provideanswers to these questions would take

place up in the air.38

The first dedicated throttles-only controlflight test arrived the morning of 2 July1991. In the summer, Dryden flightresearch often starts at the crack of dawnbefore the thermals produce strongupdrafts. Sometimes the hangar crewbegins as early as 2 a.m. These momentshave a curious lookthe operations areais a world of metal and certainties but atthat sleepy hour displays all pastel colors,the desert sky before sunrise, a paleEaster-egg blue, and the airplane glim-

mering softly like a reflection. Fullertonstrolled out to the F-15 with his test cardsclipped to his sleeve, ready to take thisproject to the next stage. But although theteam had anticipated some problems,although they had replaced one enginewith an identical mate to the other, they

were not prepared for what happenednext.

The flight did not go as planned. Fullertontook off in the sleek fighter and thenbrought the F-15 up to altitude to beginfollowing his test cards. He set up theairplane for TOC and in the instant joinedthe brotherhood of Haynes and Fitch atSioux City: no ailerons to control airplaneroll; no elevator to dictate pitch; no rudderto yaw a turn at command.

All Fullerton had was his hand on thethrottles and even before he moved them,strange things began to happen. I waslooking at the sky and then the dirt and allover,39 he remarked. When he tried agentle pressure to correct pitch, theairplane entered a roll. He reacted. Hethrottled to stop the roll. The F-15 re-sponded by pitching down, then up,seemingly with a mind of its own.

What had happened? In mid-air, in aninstant, Fullerton guessed at a part of the

Figure 10. Three-

view drawing of anF-15 airplane.

38Fullerton interview.

39Gordon Fullerton, from transcript of interview with Lane Wallace, 7 Sept. 1995.

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Figure 11. Dia-grams showing the

early F-15 simula-tion versus actual

flight in the F-15 inmanual, throttles-

only approaches at170 knots with theflaps up and the

control augmenta-tion system off.

answer. In the simulation, the mathemati-cal model had provided him with twoperfectly identical engines. But they werejust models. Even identical engines hadslight differences. When control surfacesoperated, these minimal differences hadno effect. They were masked by the power

of the flight controls. But when youturned the normal controls off, the bigengines, with a little nudge, did big deeds.Because one engine spooled up to full

throttle sooner than the other, every inputsent the F-15 careening across the sky.40

When Fullerton brought the airplanedown the glideslope to the runway, he didso with normal flight controls turned onand at the moment of touchdown, the one

proof of the day might have seemed to be:you can never land an F-15 airplanesafely using throttles-only control. Thefaces above in the control room had a

40Fullerton interview.

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Figure 12. Bill

Burcham andTrindel Maine at an

F-15 simulatorsession. (NASA

photo EC95-43026-2 by Jim Ross).

stricken look. And surely in the hallways,the naysayers were nodding I-told-you-so.

Humbling is the word Fullerton uses insummation; its a matter of pride. I cando anything. This airplanes not going to

get the best of me. And it did. It reallydid.41 When the F-15s flight controlswere turned off, the airplane becameaerodynamically very unstable, whatFullerton called a squirrelly airplane. Asfar as his colleagues could tell, Burchamappeared unfazed. But he trudged to hiscar with a stack of test data printouts, andit was only Tuesday night. Usually, hewaited until Friday night to bring themhome. He would have the long driveacross the bleak desert to ask himself

questions. Why was the F-15 sim sodifferent from the real airplane? As oneassociate said, When Bill started to dealwith these propulsion effects and effects

near landing, there werent any guidelinesto help him . . . he was going to have towrite the book.42

* * *

The team set about making major modifi-

cations to the F-15 sim. If the sim wasimproved, they should be able to dupli-cate what Fullerton had seen in actualflight. In the first days, they realized thatthe F-15s center of gravity (CG) shiftedas the fuel was consumed, and theairplanes weight and weight distributionchanged. They modeled the sim toincorporate this data. The F-15 went to asecond flight test, but the results remainedpoor. Fullerton could maneuver somewhatup and away, but the F-15 without control

surfaces was an unstable airplane. He didnot have anywhere near enough controlfor a safe landing. When he pushed thecollective throttles up, the airplane rolled.

41Fullerton interview with Lane Wallace.

42Burken interview.

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Figure 13. Featuresof the PCA system

on the NASA F-15HIDEC airplane.

A series of tests followed, flights, sims.Some of this process was tweaking andde-bugging. The team had larger,shadowy factors to discover, and one ofthem turned out to be inlet effects.

Trindel Maine, a Dryden engineer who

joined the team at this stage and had areputation as a wizard at scanning datasheets and spotting a trend, saw theprocess for what it was. A dauntingnumber of factors come into play when anairplane maneuvers with throttles, and theresearcher at last brought this one to light.The big, overhanging ramp-air inlets arebeside the pilot. It turned out that whenFullerton wanted the nose to drop andpulled the throttles back, the reducedairflow to the engines pushed up on the

inlet ramps and raised the nose. Thiseffect is normally masked by the pilotscommanding a minor change in theelevator position, but with no elevatormovement, the inlet effect caused theairplane briefly to pitch in the wrongdirection. The Dryden and McDonnellteam developed a model of the inlet effectand added it to their simulations atEdwards and St. Louis. Now the TOC in

the F-15 sim went up a notch in difficultybut still did not match the flight researchdata.

Another problem involved the groundeffects. Ground effects is a black art, saysTrindel Maine; we just dont have any

good ground effects models out there.43

Some ground effects studies do exist, butthey are based on fixed throttle settings andare not well modeled. Normal flightcontrols operate so powerfully, they maskground effects. When the F-15 came withina wingspan of touchdown, it entered thisrealm of unruly aerodynamics.

The engineers needed ground-effects datathat were non-existent. This was an areawhere the simulator model was suspect

. . . where we were quite concerned aboutknowing what wed be dealing with,explains Maine. The team commissioneda study addressing ground effects on F-15landings.44 The study was conducted inthe traditional fixed-throttle setting and,as a consequence, did not match very wellwhat the team encountered afterwards inPCA flight. The final answer didntbecome clear until much later, Maine

43Trindel Maine, interview with author, 2 July 1998.

44See Stephen Corda et al.,Dynamic Ground Effects Flight of an F-15 Aircraft(Edwards, CA: NASA TM 460, June

1994).

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Figure 14. GordonFullerton climbing

aboard the F-15 forthe 21 April 1993,

research flight.(NASA photo

EC93-41034-4 byLarry Sammons).

remarked. . . . the PCA control lawsmoving the throttle actively during thelanding phase had a big impact on howthe ground effects actually affected theflight path. As it learned more aboutground effects, the team worked tominimize the most severe effect, an

alarmingly high sink rate just beforetouchdown.45

In addition, the engineers modeled thesims more closely to the Pratt & Whitneyengines, identifying lags and rate limits.They put modeling in the sim for landinggear and its actual effects on aerodynam-ics. Gyroscopic movements from thepowerful engines were factored in. Butdespite all these efforts, flight difficultiespersisted.

Some unmodeled effect was obviouslypresent, said Burcham. The team had notsolved this mystery, but it hoped that thecomputer and the feedback sensors of thePCA system would be able to accommo-date the problem. It was time to see, saidBurcham, if the PCA systemwith the

computer taking the pilot inputs, factoringin the sensor feedbacks, and figuring outwhere to put the throttleswould work.46

In the early weeks of 1993, Fullertonconducted the initial flights with the PCAsystem engaged. PCA showed muchimprovement over TOC, but still presentedsome problems. The noisy signals fromsome of the sensors required filtering, andbank angle feedback was needed. Fortu-nately, back in an earlier design review,

45Maine interview.

46His comment on a draft of this narrative.

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Figure 15. Gordon

Fullerton and BillBurcham next to

the F-15 aircraft.

(NASA photoEC93-41034-11 by

Jim Ross).

Glenn Gilyard had noticed that the bankangle was not one of the feedback sensorsand had it added. Ed Wells had introducedflexibility into the test process by makingavailable points in the software where thepilot could select variable gains, filters,multipliers, and gain schedules. It pro-

vided a quantum leap. The researcherscould carry on real-time dialogue over theradio with the pilot and alter PCA. It wasworking fastit was depending on asmall team of highly skilled individuals.47

With the changes, the team improvedcontrol enough to try low approaches tothe runway.

Many standards apply to landing anairplane. Some resolve to this questionduring a commercial aircraft landing:

would your coffee stay in its cup (assum-ing the flight attendants had not collectedcups before landing, as they normallydo)? But others resolve differently: doyou walk away with your life? PCA is

47Jim Urnes, interview by telephone with author, 26 June 1998.

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Figure 16. Three-view drawing of the

McDonnell DouglasMD-11 research

airplane.

defined by catastrophic alternative. In

fact, later, PCA had the robustness tomake landings so smooth they weredifficult to distinguish from normal ones.

On the morning of 21 April 1993, how-ever, when Gordon Fullerton flew the F-15 on the downwind approach toEdwards runway, he did not have theword gentle in his pilot cards. He usedthe PCA system for a series of approachesat altitude at different trim speeds, andthen he brought the F-15 down near

ground level. When we flew within 10feet, we knew we had success, recallsJim Urnes, the McDonnell project man-ager.48

On the next flight, Fullerton made aero-nautics history when he flew the first PCAlanding. He descended in a very shallowapproach to 20 feet above the ground;then his sink rate rose quickly to 8 feetper second. The unfazed Fullerton,however, remained confident and brought

the F-15 to a firm but acceptabletouchdown 6 feet left of the runwaycenterline. Smoke flew off the tires,

remembers Urnes.49 Nevertheless, thesystem had landed an airplane.

The system might not pass the coffee-cuptest. But it could get you safely down.

It was like landing on the moon, recallsone project manager about the applausefor the F-15 landing that erupted in theDryden control room and echoed aroundthe industry for weeks to come. Look MaNo Hands trumpetedAviation Week &Space Technology.50

In a real disaster, PCA would be thetechnology of last resort for first-timeusers. The team addressed this issue afterthe F-15 landings, when it invited sixpilots unfamiliar with PCA to test ap-proaches and go-rounds. All the pilotsflew the system successfully and wereenthusiastic about PCAs capabilities.Pitch control was awesome, said NavyLieutenant Len Hamilton. He indicatedthat he would rather have PCA than the

backup control technology in his currentF-14.51

48Urnes interview.

49Ibid.

50See Michael Dornheim, Industry Outlook: Look Ma, No Hands,Aviation Week & Space Technology (3 May 1995): 11.

51See Appendix D for guest pilot remarks at greater length.

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The engineers, pilots, managers, all of themhad understood one brutal point about theindustry position: until you proved thistechnology on a small airplane, you had nochance of getting on a big airplane. Nowthat they had proved it on the F-15, the nextairplane waiting for PCA was the MD-11.

The MD-11 is a widebody transportairplane that succeeded the earlier DC-10, ahuge three-engine vehicle more than two-thirds of a football field in length. The MD-11 with its full flight control autolandsystem, its digitally controlled engines, andfully integrated design was a next-genera-tion aircraft, the type of aircraft that was inthe cards from the day the idea wassketched on the napkin.

Even before the historic PCA landing of theF-15, efforts were made to arrange PCAexperiments on a large transport airplane.One crucial moment occurred during ameeting at NASA Headquarters in Wash-ington, D.C.

In December 1992, Dwain Deets, thenActing Director of Dryden ResearchEngineering, attended this pivotal Head-quarters session. Assembling around theconference table were executives from

every big player in aircraft manufacturingand also the directors from the other NASAcenters. Bob Whitehead, Director ofSubsonic Transportation in the Office ofAeronautics and Space Technology atHeadquarters, convened the group. Szalaihad asked Deets to attend and representhim, and Burcham attended as technicalsupport.

Deets had spent many years as a Drydenspokesperson in Washington, D.C., meet-ings. He recalls a sense that day of ventur-ing into hostile territory. The issue wasendorsement. Whitehead would not let thecenters proceed on a project unless they hadindustry endorsement. From the start,Boeing had been very cool to the idea ofPCA. Whitehead was not looking for mere

industry neutrality. Whatever it is we do,he was quoted as saying, its got to buy itsway onto the airplane. Another concern forDeets was NASA Langley, the center thatspecializes in subsonics. Burcham and hiscolleagues were venturing on Langley turf.Burcham had already briefed Langley about

PCA and had not been well received. In thefuture of this technology, there would ariseremarkable cooperation between Langleyand Dryden. But at that time, observersrecall, jealousy was often the norm betweencenters. And it did not help that a series ofrecent promotions to Headquarters hadgone to Langley execs, many of themadvisors to Whitehead.

Whitehead, however, when he opened themeeting spoke favorably about PCA. He

was brief; he did not cajole, debate, orinsist; and Deets had the distinct sense ofwatching a referee toss a ball into play atthe start of a contest. When his turn came,Deets gave the briefest of presentationseveryone at the table knew what the issuewas. Next, the floor moved around the tablefrom one executive to another. John King,from McDonnell Douglas Aerospace inLong Beach, gave an extremely strongendorsement. So did NTSB member JohnLauber. Finally, came the turn for the man

from Boeing.

I never saw anything like it, Deetsremembers today with a touch of wonder-ment. He didnt say anything. Everyone atthe table had their eyes fixed on him. It allhinged on this moment. But he didnt say aword; he just glared down for quite sometime, the room utterly silent, and then hemade a quick movement; he made thisthumbs-up sign. That was all, that was that. . . it was a done deal.

The meeting moved quickly to other itemson its agenda. When Deets and Burchamreturned to Dryden, they brought homegood news.

Its a go, they said.52

52Dwain Deets, interview with author, 1 July 1998.

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The MD-11 experiment was destined to bemuch more successful than the F-15. Butthe crises to be faced were different andthese had nothing to do with harrowing testflights. The crises occurred in well-cush-ioned conference rooms. Now the projecthad a $2.5 million budget line per year

resulting from the advisory meeting inWashington. Now there were contracts,subcontracts, and work orders rather thanreliance on the good nature of an engineerat the end of a long day. And there was theassignment of a project manager fromNASA Dryden, first Russ Barber, then BobBaron, and finally Joel Sitz ably guiding theproject through NASA internal processes.Dryden engineers now included TrindelMaine, John Burken, and Burcham, andmeanwhile Fullerton invited another NASA

pilot, Dana Purifoy, to join in the flightresearch. New faces appeared becauseMcDonnell Douglas Aerospace in St. Louishad developed the F-15, but the DouglasAircraft unit in Long Beach and Yuma hadthe MD-11 under active development. Theproject assembled talented test pilots JohnMiller and Ralph Luczak as well as WaltSmith for simulation studies. The remark-ably ingenious engineer Jeff Kahler wassent by Honeywell to install the PCAsoftware in the flight control computer ithad manufactured. During these early days,GE and Pratt & Whitney, manufacturers ofengines slung on MD-11s, sent engineers tothe meetings. It was anyones guess whatengines would be attached when they at lastfound their specific testbed.

The MD-11 sims developed nicely. Yousure you guys turned the button off? askedone guest pilot, a comment that wasrepeated for months. But although flight

controls were turned off and PCA engaged,something else subtly was turned off.Months passed; an inertia began develop-ing. One resident expert from McDonnelladmitted off the record, This scared me toturn off all the traditional flight controls.

Burcham had shepherded the PCA into anew environment. At his own desert lab,debate had been informal, personal, and in-your-face. Douglas Aircraft was corporate,pleasant, and polite. A subtle transition hadbeen madehe was no longer an associatebut a client.

The project had some difficulty, remem-bers Russ Barber, in transitioning from simstudies to airplane modifications andoperations. We kept going down to LongBeach for reviews and we kept getting moreand more sims.53 Burcham does not like totalk about the period.

What was the problem? It was, in the end,economics. None of the commercial airlinemanufacturers will specify a sticker price on

their wares. But when you see a jumbojetliner on the runway, you may be lookingat as much as 150 million dollars. Whowould lightly take such an expensiveproduct and, in terms of safe flight, gobackwards? Who would risk it? Burchamhad at last gotten a budget for PCA, butwithin the parameters of the industry, hewas still on a shoestring.

Although Douglas produced MD-11s, it didnot own a single one. The firm did not keep

its 150-million-dollar product on the shelfas if it were retail. The issue became: couldBurcham get an airplane?

Burcham himself had worn the projectmanager hat whenever needed; his newLong Beach technical associate, JohnFeather, played that role now in a part-timecapacity. In addition to engineering duties,Feather filed applications and attendedreviews in efforts to find a real airplane. Butall negotiations proved fruitless. At this lowpoint, even as Burcham spent hours on thephone, in his phrase going round andround, he at last talked Douglas Aircraftinto appointing a full-time project manager.The man appointed was Drew Pappas.54

53Marvin R. Barber, interview with author, 18 June 1998.

54Frank W. Burcham, interview with author, 17 June 1998.

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When Drew came on, recalls RussBarber about the first week in June, 1994,almost overnight it turned around.55

Pappas is a short balding man with a darkmustache who insists on modesty. I wasalong to carry the bags, he says. But asmany elements fell into place at his touch,

it became clear Pappas knew DouglasAircraft very well. He knew how thingsgot done, where the procedural gearsturned, how to keep the regulatoryprocess from jamming. I have a Mr. Fix-It mind, he grins. When I dont knowwhat to do, I try to get the answer and fixit. He dismisses what he does asmother-henning, and he sees himself asa professional worrier, the detail-cruncheralong for the ride with genius.56 Within arelatively short time, he found them an

airplane, the testbed, the MD-11. Hemother-henned a 150-million-dollarairplane onto the runway.

The project regained momentum, confi-dence returned, but a surprise awaitedPappas. Doubts about PCA still troubledsome of the most distinguished membersof his team. One afternoon at a simulationin Long Beach, two colleagues spoke up.These men had flown TOC and knew itwas rough. They anticipated two problem

areas: the degree of complexity in thelanding and the design of software tohandle the challenge of actual flight. PCAtechnology might never work, theywarned.

Pappas recalls driving home stunnedafterwards. Now the questions whirled inhis mind. The implications began to settlein. He wondered if the doubts voiced byhis team members would become a self-fulfilling prophecy. He hesitated before a

step both unpleasant and risky. What if Irequested changes in personnel? heasked himself. Are these guys going tokill my project, or worse, are they right?

By the time Pappas pulled in the drive-way at home, he had reached a decision.

He would request no roster changes; hewould re-focus his own horizons. Myobjective, he explains, was not toachieve success, but to determine if thetask was feasible.57

Flight 232 pilot Al Haynes had raised anissue after he enthused about PCA. Howdo you reduce the speed of the airplane?During this stage, the engineers found theanswers always proved specific to theairplane. Some airplanes have electroni-

cally-commanded stabilizers which, evenwith hydraulics failed, will reduce speed.Others have electrically or pneumaticallyoperated flaps that drop and reduce speed.Moving the center of gravity to the rear ofthe airplane can also reduce speed.Lowering the landing gear slows theairplanethe open wheel wells andhinged landing gear doors produce drag.Many factors were found to influenceairplane speed.

Douglas Aircraft introduced numeroussafety checks and procedures into theseexperiments. In fact, at first only oneengine flew PCA in actual flight. But onthe historic date of 27 August 1995, whenFlight 221 went up over Yuma with bothengines PCA-equipped, the system onceagain showed its surprising capability.58

The pilots took the airplane to 10,000 feetaltitude and turned the PCA system on. It

performed as smoothly as a normal

55Barber interview.

56Drew Pappas, interview by telephone with author, 17 July 1998.

57Pappas interview.

58The designation Flight 221 does not refer to the number of research flights in the PCA program. Rather, the

number designates the flight in the total series of test flights performed by the specific MD-11 on any number of projects.

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autopilot, holding the wings level, control-ling flightpath to a few tenths of a degree,maintaining altitude to within plus or minus20 feet. As his eyes moved over the panel inthe cockpit, safety pilot John Miller becamea convert. On the first attempt, I under-stood the capability of the engineering team,

and they had done a fantastic job.59

Millerproved a powerful advocate for the mostcompelling proof, a real MD-11 touchdown,and it was Miller who begged landings andother test envelope expansions fromDouglas management.

As the MD-11 tests had moved to loweraltitudes that August, the thermalsupdrafts off the blazing Arizona sandshadbegun to pose a significant challenge,especially in the afternoons when tempera-tures soared to 115 degrees. Kahler andBurken had worked feverishly to developcontrol law changes to improve PCAs

tolerance to gusts and thermals.

On 29 August 1995, the MD-11 made itsfirst PCA touchdown. The day started earlyat the Douglas airfield in Yuma. The crewbrief was at 4:30 a.m. in Yuma, recallsBurcham, with takeoff just as the sun rose

over the desert mountains. With themodified software installed, the engineeringcrew and pilots flew north that morning.Their destination was Edwards Air ForceBase, with its vast natural landing siteadjacent to Dryden and the main runway atEdwards where they would land. It was

home in a sense, marginally more forgivingthan Yuma in thermal intensity, and defi-nitely friendlier in the length and width ofits runways. At Edwards, Fullerton com-pleted successful approaches to 100 feet, 50feet, and 10 feet above the runway. As he

finally approached for actual landing, thethermals began to buffet the airplane, yet,Burcham recalls, Fullertons approachlooked good. The pilot left the flightpathcommand at -2 degrees, working theheading knob. At 100 feet he made theflightpath shallower, and the airplane camedown smoothly at a sink rate of 4 feet per

second on the centerline. Here was all thepromise of the F-15 flights delivered homenow in the landing of a commercial airliner.The videotape records it: the vast birddescending with all control surfacesmotionless, an exhilarating but eerie sight.60

Figure 17. Pilot

views of MD-11performing a PCA

Instrument LandingSystem-coupledapproach and

landing.

Figure 18. MD-11touching down for

the first time underengine power only,

11:38 a.m. August29, 1995, atEdwards. (NASA

photo EC95 43247-4 by Dennis

Taylor).

59John Miller, interview by telephone with author, 19 June 1998.

60Based on a description of the landing written by Frank W. Burcham on the original draft of this account.

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On 29-30 November 1995, landings atEdwards demonstrated an improvementdating back to Joe Conleys inspiration,the addition of ILS coupling to PCAsarsenal of signals. Kahler connected thePCA and ILS software in the Honeywellcomputer on the MD-11. The result

brought improved control to PCA and didnot require additional emergency-proce-dure training for pilots. Kahler also addedan autoflare to PCAs arsenal for these two

landings, an improvement that demon-strated a feasible step toward hands-offemergency touchdowns.

In the fall of 1995, two dozen guest pilotsfrom the major powers in commercialaviation were given the opportunity to

operate PCA on the MD-11, flying anILS-coupled landing to 100 AGL (100feet above ground level) before initiatinggo-round.61 The pilot comment cards

Figure 19. Re-

search pilot GordonFullerton, project

engineer BillBurcham, control

engineer JohnBurken, McDonnellDouglas John

Feather, and

McDonnell Douglasproject engineerDrew Pappas

emerging from theMD-11 at the NASADryden ramp after

the first PCAlanding in the MD-

11. (NASA photoEC95 432351-3 by

Tony Landis).

61See Appendix F for remarks from the two-day guest pilot session.

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thundered with wonder and praise, butbeyond the hurrahs from demonstrationand experiments was another experimentsometimes overlooked.

* * *

The ultimate test for PCA would be toturn off all the hydraulics. The flight testshad locked down all the surfaces, theailerons, the rudder, the flaps, but in a realcatastrophe, the surfaces wouldfloattosome position. Would it be a good posi-tion or a bad one? The sims had madepredictions, forecasting a rather benignpitchover to a higher trim speed. The truthwas uncertain. To turn off all hydraulicsmight start a deadly scenario. What wasthe worst that could happen? The result

might be what the engineers call ahardover, a dramatically asymmetricposition, and because the ailerons creatingit have a more powerful effect than enginecontrols, the engines could not power theMD-11 out of it.

Burcham saw it as a crux issue. JohnMiller brought something close to thephysical courage he used in test pilotingto the task of pleading this case. To theshock of all involved, he convincedmanagement. Douglas gave them the go-ahead.

It was to be an ultimate test at the humanlevel, too. On MD-11 flights, the engi-neers traveled at the rear of the airplane,sharing the risk that typically pilots facedalone. Observers at Douglas still speakwith awe about the engineering team thatpored over test displays and made signifi-cant changes in flight to gains and lags via

intercom conversation with the pilot.Some projects might take three weeks toarrive at the same results. Some engineersmight spend whole careers working onprojects that never took them outside thelaboratory.

It was a bit eerie, recalls Joel Sitz,Dryden project manager when he remem-bers the change from dealing with PCA aspaper and reports to actually being there.The vast hollow plane stretched dimlyinto shadow, no seats, no carpet, nopaneling. As the pilot flew TOC, Sitz

couldfeelthe airplanes shuddering, hearthe big engines slowly revving up on oneside and dying down on the other.62

Hey, this is what test pilots do everyday, John Burken remembers thinkingwhen he peered out the MD-11s cockpitwindows. As an engineer, he realized,you get numbedand probably youshouldnt. Burken has a sharp memoryof summer turbulence over Arizona. Itwas a very hot day, Yuma in August, he

recalls. The engineers were at themonitors in back and the monitors wererocking back and forth. One man wasturning greener and greener.63 Duringthese experiments, one engineer attachedto the project refused to go up on theflight tests, and once when he was sched-uled, anxiety so overwhelmed him that hebecame physically ill and checked into ahospital. But at the personal level, he tooreached his small triumph eventually,he went along on a research flight.

After the successful landing in August,Dana Purifoy substituted for Fullerton asresearch pilot and in September flew theMD-11 to an airspace over the Pacific thepilots call Whiskey Area, an emptinesswhere few commercial airliners fly andwhere pilots are able to do freeflight withfew air-traffic-control constraints andwith no compromise. Here after tests ofPCA engagement at altitude and tests oncenter-of-gravity issues, the crew com-pletely shut down two hydraulic systems.The airplanes control surfaces assumedan asymmetric position, and trim speedincreased. But PCA still dominated withrough control. The final step in these

62Joel Sitz, interview with author, 18 June 1998.

63Burken interview.

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investigations, however, did not comeuntil two months later when Fullertonreturned to flight over the desert beyondEdwards.64

In November, Fullerton took the MD-11on a flight out over the Mojave to test

PCA with absolutely no hydraulics. ForBurcham, this trip was ultimate. Hehimself always downplays any humanitar-ian angle, insisting that the crash of Flight232 at Sioux City is a mere locus in thechain of events, but the evidence is, Flight232 is a benchmark. When the MD-11tests were arranged, Burcham had theengine at the tail pulled back near idle and

the two wing engines provided thrustcontrol, the very configuration of Flight232. As the technology developed,Burcham went out of his way to invitepilots Dennis Fitch and Al Haynes to tryout PCA in simulations at Dryden andAmes. When any guest pilot went up,

Burcham first handed the flier the situa-tion that existed in midair out over Iowa in1989.65

Behind Burchams data sheets, the flowcharts, diagrams, and equations, therewas, if you stopped to look, a vision, amemory of the crippled transport in itsbizarre journey; behind the benevolently

Figure 20. Diagram

showing how muchthe flight envelope

for the MD-11expanded (in termsof altitude in feet

and speed in knots)during flight

research.

64The account of the Whiskey Area flight is based on interviews with Burcham, Miller, and Maine.

65Although I could list other test procedures that duplicate the circumstances of Flight 232, that might belabor the

point. To be fair, there is another viewpoint about the motivation for using only two engines for thrust control. Trindel

Maine wrote to this point in the original draft of this study: Note: one of the major motivations for putting most of our

PCA development effort on the MD-11 into just the two wing engine configuration with the center engine pulled back

was to keep the research generic and applicable to other airplanes. Building a system that was critically dependent on the

center engine would not easily be generalized to the much more common matched pairs of wing engines only [in the

commercial transport fleet]. We didnt want to design a system solely for the MD-11; we wanted to demonstrate a

general capability.

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shaped curves of the phugoid in reports, aremembrance of something else, thetwisting frantic rush of the airplane atimpact, its bent metal gouging an 18-inch-deep hole along 4000 feet of Runway 22at Sioux Gateway airport.

For the last hydraulics-off test on 28November 1995, a third pilot, RalphLuczak, joined the PCA team in the centerseat of the cockpit. While Miller andFullerton handled the controls, Luczakswitched off the hydraulics systemsfirsteach one separately, next each combina-tion of two, and finally all three systems.And then the team sat, waiting to see whatthe result would be. The elevators did notmove at all. The ailerons moved up,outboard aileron at 12 degrees and the

inboard one less than half as much. Therudder did not budge. It was not a catas-trophe, but these floating surfaces resultedin a nose-up pitch and caused a lower trimairspeed, the opposite of what had beenpredicted. The investigators had preparedto deal with the reverse. Because airspeedwas then trimmed near minimum forflaps-up flight, they briefly turned ahydraulic pump on to increase speed.Once this was accomplished, Luczakagain cut off all hydraulics, and afterreaching a stable speed of 212 knots, thepilots proceeded with the test cards. Theylowered the landing gear with an emer-gency system not requiring hydraulicpressure. The speed dropped another 17knots. They flew a landing approach ataltitude, and the track and pitch controlsbehaving normally.

The test was done.

Since these triumphs, PCA has taken adifferent path. If the technology getsattached to commercial airplanes, PCAmust survive FAA certification. On thelast day of the MD-11 demonstrations, anFAA guest pilot addressed this step.Conceptually . . . a very good idea. Thisdemonstration effectively shows the

potential for practical implementation,wrote the FAAs Tom Imrich, adding,more work is needed in order to move tothe regulatory credit stage.66

One regulatory stage obstacle was retro-fitting. PCA technology requires aircraft

with full authority digital engine controls,a modification that is the wave of thefuture. Unfortunately, two thirds of theairplanes now in commercial airline fleetsdo not yet have these advanced controls,and these airplanes will remain opera-tional for perhaps twenty-five years. Forlegal reasons, the industry will notmandate safety regulations on only afraction of the fleet. Many observersnoted this problem even as they ap-plauded the MD-11 demonstrationsthey

viewed the day as a glimpse into the far-off future. But Burcham refused to look atPCA as a this-will-benefit-your-grandchil-dren technology. He believed it couldbenefit members of your immediatefamily within the next few years.

While he was at a PCA design review inMay of 1995, Burcham hit on the ideathat later became the basis for simplerPCA systems. Most airplanes have anautothrottle system to maintain a selectedspeed, much like the cruise control in acar. During a conversation about trainingcosts with a Delta pilot, he first sketched,on another cocktail napkin, the concept ofusing an autothrottle for the pitch PCAfunction. Back at Dryden, controlsengineer John Burken later did an analysissuggesting that the autothrottle could doalmost as well as the full PCA system incontrolling pitch.

Burcham later used this modified systemto eliminate the need for changes to theengine control software. Most newerairplanes have not only an autothrottlesystem but also a digital thrust trimsystem. At first Burcham called the newapproach simplified PCA, but KenSzalai soon re-christened it PCA Lite.

66Tom Imrich, unpublished NASA Dryden pilot test cards, 30 November 1995.

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To operate in PCA Lite, Burcham decidedto run the pitch control through theautothrottle and use the engine thrust trimsystem, which despite a plus or minusfive percent limit,67 had enough rangelaterally for landing.

After the MD-11 tests concluded, PCAentered a new stage of development withthe Dryden researchers working in closepartnership with researchers at the NASAAmes Research Center in the SiliconValley. Ames provided advanced simula-tion testbeds with dramatically realisticeffects. Led by John Bull, a NASAveteran now working for CAELUMResearch Corporation, these researchersdeveloped an effective full PCA systemfor the Boeing 747. They also ran tests

with great success demonstrating PCA onsimulations for generic commercialairliner models. When Burcham requestedsim tests for PCA Lite, Bull and hiscolleagues produced effective demonstra-tions. Tests confirmed they could expandthe number of airplanes available forPCA, make this new version cheaper, andfly reasonably well with PCA Lite.68

The older airplanes that did not havedigital engine controls required a different

solution. The next innovation addressedairplanes having autothrottle but noengine thrust trim system. Burchamcalled it PCA Ultralite, an arrangementrequiring the pilot to manually operate thethrottles for lateral controla possiblebut difficult workload. PCA Ultralite byitself did not work well, but the Dryden-Ames team added an improvement, usingthe flight director needle in the cockpit.This step allowed the pilot to get effectivelateral control by moving the throttlesbased on cues on the flight director

needle. Pilot evaluations at Ames in 1998confirmed the results.

After successful Lite and Ultralite demon-strations, much remained to sift. Therequirements of FAA certification are ascomplex and multilevel as the product it

safeguards. Certification was not one bigtest. Rather, it was a proliferation ofsmaller tests, crucial in every case. Sincethe MD-11 days, the researchers haveexperimented on the C-17, a military jettransport that in many ways is character-istic of the next generation of largeairplane. They have flown extensiveBoeing 747 and Boeing 757 simulations.Experiments have included flying TOCtests on the U.S. Navy F-18. This newstage of experiment has involved flying

many airplanes, dealt with a great varietyof damages and looked at employing PCAas one element in post-catastrophereconfiguration. The engineers haveshown how a commercial airliner withoutflight controls and without an operatingengine on one wing can engage PCA byusing fuel transfer to offset the center ofgravity toward the operating engine. JohnBull and his colleagues at NASA Ameshave fashioned a brilliant sim demonstra-tion: the Boeing 747 has its hydraulics

fail at 35,000 feet, rolls until it is upsidedown, and then the PCA mode is en-gaged. The airplane rights itself, levels itswings, and comes in for a safe landingnearly identical to a normal auto land-ing.69

If PCA prevails, however, it will not bebecause of brilliant technology. As manyobservers will tell you, the decision willbe political, and in a multibillion-dollarindustry and regulatory web, politicalmeans financial.

67That is, plus or minus five percent of the full range of engine operation.

68See Frank W. Burcham, Using Engine Thrust for Emergency Flight Control: MD-11 and B-747 Results(Edwards, CA:

NASA TM -1998-206552, May 1998).

69The sources for this section are mostly interviews with Maine and Burcham. Also see John Bull, Piloted Simulation Tests

of Propulsion Control as a Backup to Loss of Primary Flight Controls for a Mid-Size Jet Transport(Moffett Fi

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Touchdown the Development of Propulsion Controlled Aircraft at NASA Dryden

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