*MAST BUMPING

ANDY MCKAY - AVIATION EXAMINERNZHA JULY 2015

* CAA Initiatives

Education - A back to basics approach, modernize the training material. (New RHC DVD, presentations on key topics, vector articles.) Concentrate on the flight examiners to filter down.

CAA review of RHC safety awareness training in particular how its delivered, by whom and for what types. The TAIC focus was for CAA to align better with SFAR-73 – due for completion now 1 August 2015

The CAA is conducting investigative analysis around certain aspects of Robinson Helicopters. This investigation is still ongoing and is due to be completed in the last quarter of 2015.

* Key TopicsEnergy Management (Autorotations)

Mast Bumping

Low “G” Hazards – Flight into Turbulence

Low Rotor RPM Blade Stall

RHC safety notices review

• Applicable to two bladed semi rigid Teetering Rotor heads.

• Most Common Types operated in New Zealand. Bell 212, Huey, FH1100, Bell 206 series, R66, R44, R22.

This part of the head Flaps down (Coning hinge bolt in the spindle) and

Contacts or “Bumps” the Mast here

*Simply on an teetering head

• First identified as a real problem during the Vietnam training era mid 1960’s with the US army having many unexplained crashes in the HUEY. Primarily during low level operations.

• Accident signature was a catastrophic failure in the Rotor Head resulting in fatalities.

• Lead to the US army investigating and result was an education program on “Mast Bumping” that despite its age is still used as a training tool today. Refer Youtube\Mast Bumping in Helicopters - US Army Training Film - Ella73TV.mp4

• The heavier helicopters have a more robust Mast that can withstand more of a “bump”. However there is also debate that heavier Helicopters are much harder to recover from Low “G”

• Whereas the lighter helicopters are more prone to low “G” and have virtually no tolerance to a Mast Bump. But recover much faster with the right control input’s .

• Mast Bumping is a significant topic in Robinson Safety Awareness training

*NZ Robinson Helicopter Accident Record

• There have been 237 Robinson helicopter accidents since the first one in 1982.

• The accidents have resulted in 43 fatalities and 24 serious injuries.

• 204 of the accidents have involved R22s, with 35 fatalities and 21 serious

injuries. (Mostly in the early period)

• The R44 has been involved in 32 accidents with 5 fatalities and 3 serious

injuries.

• There has been 1 fatal R66 accident.

• Robinson Stats state that 9% of the fatal Robinson accidents can

be attributed to Low “G” Mast Bumps

• Robinson accidents in NZ sit within that band. However for a

number of reason’s is now a major focus.

*Lets Get Technical

In normal flight flapping restricted to 2 degrees as G force keep’s disc and fuselage (therefore Mast) aligned

Flapping limit 9 degrees before contact with the Mast by spindle/ hinge bolt R44 / grip on B206

On an unloaded disc the blade can flap unrestricted until it contacts the mast as not enough G force to keep both disc and fuselage aligned

So if the limit is 9 deg, and during low “G” the disc shifts to an 5 deg angle due to T/R Roll. (refer vector article) The Pilot then applies left cyclic of 4 deg (to counteract the roll.)

4 + 5 = 9

Youtube\Flight 436, Trace 4 - Cyclic pushover, 111 KIAS, Chase Helicopter, High Speed Camera.MTS

Pages_from_CAA150403-Vector-May June 2015-V3.pdf

Youtube\Flight 436, Trace 4 - Cyclic pushover, 111 KIAS, Cabin GoPro Camera.mp4

Youtube\Flight 436, Trace 4 - Cyclic pushover, 111 KIAS, Chase Helicopter, ENG Camera.mp4

Youtube\Mast Bumping in Slow Motion.mp4

* Video

* General Observations• Mostly fatal. Therefore very few survivor stories

• Mast Bumps in the early ERA of Vietnam was during low level “Nap” of the earth flying. Usually tactical after a Low “G” push over crossing a ridge.

• Today we generally only see Low “G” Mast Bumping accidents in low inertia rotor heads.

• Typically the heavier mast in the HUEY could withstand 4 good rotational Bumps before separating the Mast. The lighter Rotor heads 1-2 Bumps.

• In most cases of Low “G” Mast Bumps the blade will impact on the front right cabin. (as opposed to a rotor stall whose signature will impact and separate the tail boom)

• Most of the accidents are at a cruise altitude and are a result of improper control inputs encountered in turbulence. To a lessor degree after a Low “G” pilot induced maneuver.

*Low G Recognition• Reduced “G” or Weightless feeling. Anything below 1 G.

• Most likely in significant Turbulence

• After a “Cyclic Pushover” (could also be a spray turn or TQ turn gone wrong). Refer FH1100 video Youtube\HILLER FH-1100 CRASH DURING A DISPLAY.mp4

• Caution in any flight condition tail high (Uncommanded Roll to the Right. (If high power roll will be rapid)

• The very few survivor stories report unusual noises in the rotor head with cyclic feedback (Well advanced nano seconds from disaster). What saved them was reloading the disc and following the right roll.

DO NOT APPLY ANY LEFT CYCLIC to counteract the roll wait until the Disc is loaded.

*RecoveryFirst - Gently APPLY AFT CYCLIC (to recover from low G condition)

Second – Once the disc is reloaded Apply LEFT CYCLIC (to recover from right roll)

Third –Land immediately if Mast bumping is suspected

Whilst there has been much publicity on new techniques for recovery the CAA supports the above recovery method that has been recommended by the FAA, Bell and Robinson Helicopters for the past 40 years.

In response to Simons article on lowering the collective as a recovery method Tim Tucker CFI of RHC states :

“I don’t have any problem using the “quick stop” terminology in fact it may be beneficial because it connotes simultaneous control inputs which would be just fine as long as the upmost importance for the need for aft cyclic to return the helicopter to a positive G condition is stressed and understood.”.

*Prevention• Turbulence read my article on flight into turbulence

Vector May/June 2015. (attached)

• Slow down in Turbulence. Keep the Tail down to prevent a roll should the disc unload.

• Always be aware of your environment and weather. Don t be complacent even on nice days especially in mountainous terrain.

• Always know where the wind is coming from and its strength. Know where the “leeward side” is and respect it.

• Interestingly a good number of Low “G” mast Bumps have occurred over water or wide valley’s where perhaps the pilot was not “prepared” for significant turbulence.

• Check the upper wind’s when you are assessing weather. Calm on the ground does not mean calm up high.

• No Low “G” pushovers in any 2 bladed Helicopter.

*Parting comments from Industry

“Many experienced Pilots “Lock” there cyclic hand to there knee or side pillar to prevent un-toward cyclic movement in turbulence.”

“I agree that it'd be better to design this problem out, but unfortunately there are thousands of helicopters out there that currently have this issue. That means training and good awareness of "mast bumping" is a must.” “Don't bunt”

“When flying over undulating terrain, use the collective (with appropriate anticipation) to go up and down, and adjust the cyclic to maintain desired speed. Don't use the cyclic as an altitude controller a la fixed wing”

“The days of demonstrating Low G in flight are well and truly over.”

“What's so hard.. if its windy slow down”

1. Is the release of the Robinson SB the end of the issue now?

Robinson Helicopter has provided a modification for the blades which they will be incorporating in future blade manufacturing designs. There has been no indication that any further actions are being considered.

2. Is the blade that was cracked and sent to the USA for analysis

got a formal report on cause and is this available for release or discussion?

A report has been made on the blade by NTSB. This report was compiled as part of the investigation being conducted by TAIC and therefore is subject to the TAIC Act in terms of release of information. CAA is liaising with TAIC to establish its positon in terms of possibly releasing the report or information contained within it. Nothing concerning was raised in the report.

3. If there is a report is it endorsed by the FAA or was it conducted by Robinson themselves?

The examination and evidence gathering process has been a joint venture between TAIC, CAA, FAA, NTSB and Robinson. The report is written by NTSB and the examination has been conducted using their laboratories.

4. Are we or FAA investigating any other blade failures?

No.

5. Apart from our training consultation document is CAA conducting an investigation on the wider Robinson Helicopter issues?

The CAA is conducting investigative analysis around certain aspects of Robinson Helicopters. This investigation is still ongoing and is due to be completed in the last quarter of 2015.

6. Overloading has been identified as an issue on agricultural operations in the R44. What’s CAA doing to address the issue?

The CAA has regularly and consistently communicated with agricultural operators in reiterating that the Performance and Limitation information contained in the Pilot Operator Handbook dictates the safe operational use of the helicopter.

7. How many submissions were received to the Robinson Consultation Document released by CAA?

47 submissions were received and 80% were supportive, 10% partially supportive and 10% opposed any changes. There were some very valid points raised in the submissions that will in all likelihood see changes to what was proposed and will therefore be finally released. For this reason the deadline has been extended to 1 August 2015 for a recommendation to the director.

Questions?

Thank you