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Flight Operations Safety
Stopping on Slippery Runways
Captain David C. Carbaugh
Captain Glenn C. Spakes
Flight Operations Safety
Boeing Commercial Airplanes
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Flight Operations Safety
Landing on Wet/Slippery Runways
Landing
Information - Condition Reporting
Approach, Flare and Touchdown
Stopping
Recommended Landing Procedure
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Flight Operations Safety
Information
Weather - Winds, gust - Approach Speed
Runway condition is typically providedthree ways
PIREPs (pilot reports) - braking action - good,fair, medium, poor, nil
Description of runway condition
Snow, wet, slush, standing water, sand treated
compact snow etc. Reported Friction based on Ground Friction
Vehicle report
30 or 0.30 etc.
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Flight Operations Safety
Evaluation of information
Flight crew needs to evaluate all theinformation available to them
Information may be conflicting
For example
Braking action is good, runway description is slushcovered
Measured friction is 0.35, runway description is slushcovered
If runway is reported to have slush/standing watercovering, the flight crew should be suspicious ofbraking action reports and measured friction
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Flight Operations Safety
Slush/Standing Water Report
Hydroplaning(aquaplaning) is possible
Ground friction measuring vehicles areunreliable when the runway is covered with a
depth of contaminant that exceeds*: Water -1 mm
Slush/wet snow -3 mm
Snow- 2.5 cm
*Reference - FAA AC 150.5200-30A
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Flight Operations Safety
Landing Performance Data Availableto Crews (Boeing OM - Section PI)
Boeing performance data is provided forpilot decision making
Information published as a function of
Reported Braking Action Good - Wet runway, JAR defined compact snow
Medium - ice, not melting
Poor - Wet melting ice
For landing, Boeing recommends the use of the datalabeled poor for slush/standing water due to thepossibility of hydroplaning
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Flight Operations Safety
Sample OM - PI Slippery Runway LandingData
Data provided for
different Braking
Actions and
Configurations
Reported Braking Action
Dry Good Medium Poor
Braking Configuration
Max Manual Braking
Autobrake Setting 2
Autobrake Setting 3
Max Autobrake Setting
Autobrakes are recommended
on a slippery runwayMed, 3 or 4 are recommended
depending on airplane
Sample data is from the 737 OM
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Flight Operations Safety
Sample OM - PI Slippery Runway LandingData
Adjustments for:
Weight
Altitude
WindApproach Speed
Slope
Reverse Thrust
Sample data is from the 737 OM
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Flight Operations Safety
Sample OM - PI Slippery Runway LandingData
Actual (unfactored*) distances are shown
Based on flaps 40, VREF40 approach speed
Landing distance required includes 1000 ft of air distance
1200 for 747
Includes 2 engine reverse thrust*Note: JAROPS data
includes a factor of 1.15Sample data is from the 737 OM
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Flight Operations SafetyCrosswind Guidelines
Reference: Boeing Flight Crew Training Manual - 747-400
Published in theFlight Crew Training Manual
Guidelines - not limitations
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Flight Operations Safety
Landing on Wet/Slippery Runways
Landing
Information
Approach, Flare and Touchdown
Stopping
Recommended Landing Procedure
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Flight Operations Safety
Landing -Approach, Flare andTouchdown
Objective Position the airplane on the runway at the target
point at the minimum speed for the existingconditions.
Minimize the air distance
Maximize the stopping distance available
Factors that influence air distance
Flare technique
Approach speed Approach path
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Flight Operations Safety
Landing -Approach, Flare andTouchdown
Land in touchdown zone Do not allow the airplane to float. Fly the airplane onto the
runway and accomplish the stopping procedure.
Do not attempt achieve a perfectly smooth touchdown. Donot hold the nose wheel off the runway after touchdown.
After main gear touchdown, begin to smoothly fly the nosewheel onto the runway by relaxing aft control columnpressure.
Reference: Boeing Flight Crew Training Manual
D l ti R t C i
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Flight Operations Safety
Deceleration Rate ComparisonAir vs. Ground
Based on 747 at operational landing weight
Note: on airplanes with more effective reversers the ratio of ground
attitude deceleration can be 9-10 times more than floating deceleration
DecelKt/sec
Dry
Wet
1/2"
Icy
Dry
Wet
Icy
Dry
8.0
6.04.0
2.0
0.0
Floating orAerobraking
No Reverse 2 EngineReverseThrust
Wet
Icy
4 EngineReverseThrust
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Flight Operations Safety
Excess speed
Effect of "Floating"
0
5
10
15
20
0 1000 2000 3000 4000 5000 6000
Increase in Air Distance
Exc
essApproach
Speed
Normal VTD + 10
Normal VTD
Normal VTD - 10
Bleeding off excess speed during flare will increase air distance by:150 to 200 feet / knot of speed reduction
225 to 275 feet / second of additional air time
Based on 747 at operational landing weight - 4 thrust reverser
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Flight Operations Safety
Greater touchdown velocity causes longerground distance
Excess speed at touchdowneffects stopping distance
Same weight, same runway conditions
VTD
VTD + 10
Stop
Stop
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Flight Operations Safety
Landing Distance Increase due to Excess
Touchdown Speed
0
5
10
15
20
0 200 400 600 800 1000 1200
Dry
Good - Wet
Poor - Wet Ice / Hydroplane
Medium
Excess
Touchdown
Speed- Knots
Increase in Stopping Distance - Feet
Based on 747 at operational landing weight - 4 engine reverse thrust
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Flight Operations Safety
Excess Threshold Height
ExcessHeight
Increased in Distance
to Touchdown
0
20
40
60
80
0 500 1000 1500
Increased in Distance to Touchdown - Feet
Excess Height
@ Threshold
(Feet)
Based on a
3 degree glideslope
Normal 50 feet
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Flight Operations Safety
Landing -Stopping / Roll out
Objective Stop the airplane within the remaining runway available.
Factors affecting stopping distance
Reduced runway friction capability Wet
Standing Water / Slush
Ice / compact snow
Effectiveness of stopping devices
Thrust reversers, ground spoilers, wheel brakes
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Flight Operations Safety
Runway Friction Capability
Hydroplaning
Viscous - normal wet runway friction
Dynamic - planing of the tire on standing water
and slush Reverted rubber - locked wheel hydroplaning
Vi H d l i
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Flight Operations Safety
Viscous Hydroplaning- Normal wet runway friction
Thin film of water acts like alubricant. The microtexture
(sandpaper type roughness) of the
runway surface breaks up the water
film and greatly improves traction.
Airplane
Braking
Coefficient
Ground Speed - knots
Dry runway
Rougher microtexture
Smoother microtexture
D i H d l i
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Flight Operations Safety
Dynamic Hydroplaning- Commonly called hydroplaning, aquaplaning
At high speeds the tire planes on deepslush/standing water. Tire grooves and
macrotexture (stony or grooved surface)
help drain water from the footprint and
improve traction.
Airplane
Braking
Coefficient
Ground Speed - knots
Dry runway
Nil braking above 90% of
dynamic hydroplaning speed
VHP
VHP
= 8.63 Tire Pressure - psi
.9VHP
R t d R bb H d l i
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Flight Operations Safety
Reverted Rubber Hydroplaning- Locked wheel
When a tire locks up on a smoothwet or ice surface, the friction heat
generates steam. The steam pressure
then lifts the tire off the runway, and
the steam heat reverts the rubber to a
black gummy deposit.
SteamSteam
Reverted rubber hydroplaning is not an
issue on post-1980 airplane designs due
the improvement in anti-skid systemhydroplane protection.
Eff t f diti
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Flight Operations Safety
Ground
Speed- knots
0
20
40
60
80
100
120
140
160
0 1000 2000 3000 4000 5000 6000 7000 8000
Poor - Wet Ice
Hydroplane
Dry
Wet - Good
Medium
Effect of runway condition onstopping distance
Distance to Stop - feetBased on 747 at operational landing weight - 4 engine reverse thrust
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Flight Operations Safety
Effectiveness of Stopping Devices
Dry runway - Wheel brakes are the most effective
stopping devices Lift reduction due to spoiler deployment contributes
greatly to the generation of effective stopping force dueto wheel brakes
Based on 747 at operational landing weight - 4 engine reverse thrust - 120 knots
Effect of Ground Spoilers
Ground Spoilers
No Ground Spoilers
0 100,000 200,000 300,000
Stopping Force - lbs
49000
49000
54000
35000
168000
106000
Reverse
Thrust Aero
Drag
Wheel
Brakes
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Flight Operations Safety
Effect of spoilers
Total Stopping Force - (lbs ) = Reverse Thrust + Aero Drag + Wheel BrakeSpoiler Effect
Spoilers Deployed Spoilers Stowed % Stopping Force
Dry 270,100 190,400 29 %
Good 194,400 142,300 27 %
Medium 148,500 113,200 24 %
Poor 125,600 98,600 21 %
Based on 747 at operational landing weight - 4 engine reverse thrust - 120 knots
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Flight Operations Safety
0 100000 200000 300000
1
2
3
4
Stopping Force - lbs
Slippery runway - Thrust reverser and aerodynamic
drag become dominate stopping force as runway
slipperiness increases
Effectiveness of Stopping Devices
Based on 747 at operational landing weight - 4 engine reverse thrust - 120 knots
% of stopping
force which is
drag and reverse
thrust
80 %
70 %
55 %
35 %
Poor - Wet Ice/Hydroplaning
Medium
Good - Wet
Dry
Reverse
Thrust
Aero
Drag
Wheel
Brakes
0 100,000 200,000 300,000
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Flight Operations Safety
Automatic Braking
Boeing recommends autobrake whenlanding on a slippery runway
Setting 3 or 4 for wet or slippery runway
Actual setting dependent on model Autobrake assures prompt application of the
brakes after touchdown
Autobrake performance capability is limited by
the runway friction capability
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Flight Operations Safety
AFM Landing distance
VRef
Stop
Stop1.67 factor
Stop1.67 factor 1.15 wet
factor
Demonstrated Dry Capability
FAR Dry
FAR Wet
VRef
VRef
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Flight Operations Safety
Distance Comparison - Book Data
Stop1.67 factor 1.15
wet AFM - FAR Wet
VRef100 %
Stop OM - Max Manual
Stop
70 %
90 %OM - A/B 3
Stop 90 % OM - A/B 3
Good}
OM - Max Manual
OM - A/B 3Stop
110 % Poor}
Medium}
Based on 747 at operational landing weight - OM data based on unfactored, 4 engine reverse thrust
assuming a 1200 foot touchdown point.
Distance Comparison 50 Feet
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Flight Operations Safety
Distance Comparison - 50 FeetHigh and Extended Flare (floating)
Stop1.67 factor 1.15
wet AFM - FAR Wet
VRef
100 %
Stop Max Manual
Stop
100 %
120 % A/B 3
Good
}
Max Manual
A/B 3Stop
140 %Poor}
Medium}
Based on 747 at operational landing weight - 4 engine reverse thrust - extended flare data is based
on a 10 knot high approach speed bled off during the flare manuever.
Vref+ 10VTD Normal
Stop 120 % A/B 3
Vref+ 10VTD Normal
Vref+ 10VTD Normal
Vref+ 10VTD Normal
100 ft
100 ft
100 ft
100 ft
Distance Comparison 50 feet high and
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Flight Operations Safety
Distance Comparison - 50 feet high andextended flare (floating) plus No Reverse Thrust
Stop1.67 factor 1.15
wet AFM - FAR Wet
VRef
100 %
StopMax Manual
Stop
110 %
130 % A/B 3
Good
A/B 3Stop
180 %
Poor
Medium
Vref+ 10
VTD Normal
Stop 140 % A/B 3
Vref+ 10VTD Normal
Vref+ 10VTD Normal
Vref+ 10VTD Normal
100 ft
100 ft
100 ft
100 ft
Based on 747 at operational landing weight - 4 engine reverse thrust - extended flare data is based
on a 10 knot high approach speed bled off during the flare maneuver.
}
Max Manual
Summary:
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Flight Operations Safety
Summary:Recommended Procedures
Information
Evaluate all the information available beforethe approach
Wind, weather, runway condition etc. If runway conditions warrant, review the performance
data to ensure the runway length exceeds theexpected stopping distance by an adequate margin
Summary:
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Flight Operations Safety
Summary:Recommended Procedures
Prepare to land the aircraft In the touchdown zone 1000 feet target
On centerline
With minimal lateral drift Without excess speed
Normal speed additives
Arm auto spoilers and auto brakes as
appropriate Assures prompt stopping effort after
touchdown
Summary:
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Flight Operations Safety
Summary:Recommended Procedures
Flare and Touchdown
Flare should lead to a firm touchdown
Extended flare will extend touchdown
and delay braking Lower the nose as soon as main
gear touches down
Increases load on the gear
Summary:
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Flight Operations Safety
Summary:Recommended Procedures
Raise spoilers as soon as possible aftertouchdown (confirm auto spoilerdeployment)
Increase load on the gear
Initiate braking once spoilers have beenraised and nose wheels have contacted therunway
Apply brakes smooth and symmetrically
Summary:
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Flight Operations Safety
Summary:Recommended Procedures
Initiate reverse thrust as soon as possibleafter touchdown
Target the rollout to stop well short of theend of the runway
Leave margin for unexpectedly low friction dueto wet rubber deposits or hydroplaning