Gremline Flight Safety Report: Pilot vs Aircraft Limitations / Gardan Manual Error / In Brief

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Text Box: pilot vs aircraft limitations / gardan manual error

the gremline digest — pilot limitations / gardan manual error

Pilot Limitations Trump Aircraft Limitations
Most rational people will accept that just because a particular motorcycle can achieve 150mph it is not wise for the average rider to travel at that speed. Equally, just because my car has a top speed of 155mph I know that travelling at that speed is beyond my ability as a driver. Yet, it seems that because an aircraft has a published crosswind limitation of, say, 17kts, the average PPL on one of their rare ventures into the air thoughtlessly assumes that they have the ability to land their aircraft safely in a crosswind of 17kt.



We have often pointed out that the limitations published in Owners Manuals, Pilots Notes or whatever mark the outer edge of the performance envelope for that particular aircraft and DO NOT indicate something that may be safely achieved by all and sundry. Taking crosswind limitations as an example it is probably worth stating yet again that this limitation was established by an experienced and skilled test pilot operating from a hard runway on a large airfield. The figure arrived at is one that marks the outer limit of controllability, not one that should be taken as a daily target for operations. It was not established for landing on a narrow grass strip of marginal length surrounded by farm buildings and tall trees with an approach over a string of unmarked cables.
      A recent crosswind landing accident to a Piper Cherokee has uncovered yet another aspect of crosswind limitations that had not previously occurred to me. A student pilot was on a solo navigation exercise. On return to her base airfield she was told that the runway had been changed from 20 to 26 and the surface wind was 230/13 kt. She went around from the first approach because the aircraft began to drift to the right as she approached the runway. The next approach was better and the pilot did not notice any drift until after touchdown. Then a large gust caused the aircraft to weathercock to the left. The pilot tried to correct this yaw with right rudder but was physically unable to keep the rudder applied and the aircraft yawed back to the left before turning through 90 degrees and departing the runway. The nosewheel collapsed, the propeller struck the ground shockloading the engine and damaging the aircraft beyond economic repair. The pilot was unhurt.

      The pilot reported that although the aircraft had a 17 kt crosswind limit she lacked the physical strength to hold the required amount of rudder in a strong crosswind.
      The facts are taken from AAIB Report EW/G2008/11 which source is duly acknowledged.
      This is a limitation that had not previously come to my attention but is obviously something that reduces this pilot’s crosswind limit to some figure well below the published aircraft limit. Assuming that the female pilot involved was of small stature and thus had limited ability to apply and hold full rudder, this incident should warn us of the need to make sure pilots adjust their seat position and the position of the rudder pedals so as to minimise this problem. It may even be the case that a particularly petit person is not a suitable person to fly a particular type of aircraft.
      The message is that the pilot’s personal limitation overrides the aircraft’s limitation.



Gardan GY80-180 Horizon Operating Manual — Error

Owners and operators of Gardan GY80 -180 Horizon aircraft are warned that the fuel consumption curves for the Lycoming 0-360-A engine published in the Operators Manual at Chapter III page 23 dated January 1, 1966 are incorrect and show consumptions in litres per hour that are much lower than the actual consumption figures.
      The fuel consumption of the American Lycoming was calculated in US gallons per hour. The French Gardan fuel gauges and tanks are calibrated in litres thus it was necessary to provide fuel consumption figures in litres per hour.
      The error is that the consumption rates in US gallons per hour (left of the graph) do not correctly match the rates in Litres per hour (right of the graph). For example 10 US gallons per hour is aligned with 30 litres whereas it should be aligned with 37.8 litres, an error of over 12%. Pilots using these graphs to calculate fuel consumption in litres per hour during flight planning will find their aircraft using more fuel than planned. This error was uncovered by AAIB while investigating a recent accident.
The European Aviation Safety Agency (EASA) was advised of these errors by CAA and has issued an Airworthiness Directive, effective 17 November 2008 that forbids the use of the existing conversion curves and provides correct conversion data to be inserted into the Operating Manual. This will be issued to registered owners, but if you have not received this amendment, contact EASA.
      Information from AAIB Report EW/G2008/08/18 which source is duly acknowledged.

More on the Gardan
Another point from this accident investigation is the fact that the Gardan flaps lower automatically on undercarriage down selection. The pilot of the accident aircraft lowered the undercarriage while attempting a forced landing after engine failure due to fuel exhaustion. The automatic flap selection increased the rate of descent to such an extent that the aircraft struck a hedge short of the intended landing field. Have you RECENTLY practised a forced landing in your Gardan?



In Brief …..


A few brief items that nonetheless carry lessons to be considered — apart from the first, which produces no satisfactory recommendations that we can think of!


The Dog It Was That Died!

A Beech Musketeer was landing on an unfenced grass runway surrounded by open farmland. A dog was seen to run under the aircraft at touchdown. There was a loud bang and the right landing gear detached from the aircraft causing the aircraft to slew into an adjacent cornfield. The three occupants were unhurt but the dog was killed instantly by the impact.


Finals Check – Brain in Neutral?
The pilot had flown the Cessna 210L from Paris Le Bourget to Belfast City Airport and was making an ILS approach to Runway 22 in light winds and good weather. The pilot drifted slightly below the 3 degree glideslope on short finals. The aerodrome controller saw that the undercarriage was up and transmitted a warning but the aircraft landed with the gear retracted.
      The gear warning system was found to be serviceable. The pilot said the gear warning horn was not very loud and could be confused with the stall warning. Both warnings are routed through the overhead speaker rather than through the pilot’s headset. The increased power required during the shallow final approach may have delayed the onset of the gear warning horn until just before touchdown. The pilot could not explain why he did not hear the warning from ATC.


What a Performance
The pilot completed his performance calculation prior to departure from a damp grass runway 27 with a surface wind of 170 less than 5 kt and a TORA of 621 metres. He calculated his take-off run required by the PA-28 as 370 metres.
      He used full power and two stages of flap, expecting to rotate at about  ⅔ along the runway but the airspeed was still just under 60 kt at that point. He believed that he would not clear some tall trees in his path so decided to abort. Having travelled a further 30 to 40 metres he closed the throttle and applied full braking. The aircraft overran the runway end into some long grass where the nosegear was damaged.
      The pilot’s performance calculations were correct, based on the information he used but he later considered that parts of the runway were wetter than expected and that his visual assessment of the path to clear the trees was incorrect. He will review his future performance calculations more critically as he considers that less fuel on board might have improved his safety margin.
     GA Safety Sense 7C, within LASORS 2004 contains comprehensive guidance on aeroplane performance and safety margins to be applied to calculations.


Dream About Flying, Don’t Fly About Dreaming
A student pilot had flown a 15 minute circuit detail with his instructor and was briefed for solo circuits. After 45 minutes of various circuits, including go-around and touch-and-go circuits, the pilot made a final landing with full flap. There was no wind and the pilot maintained the centre-line without rudder application. The pilot then became aware that the aircraft was not slowing as expected and braking was not as effective as required. The pilot attempted to turn right at the runway end but the wingtip struck the fence. The pilot honestly acknowledged that he had misjudged the aircraft retardation in the calm conditions and had applied the brakes too late.
      Another old adage is that the landing is not complete until the wheels have stopped turning.



And Finally …

I was once flying members of a group of disabled people in a sailplane as part of a charity flying day at a gliding club. Having flown several people a very eager lady arrived in a wheelchair, bubbling over with anticipation. She was wearing slacks and a blouse. We lifted her into the rear cockpit and helped with the strapping in procedure, having already covered the safety brief. I then got into the front cockpit and checked the controls for full and free movement. There was a slight restriction in roll, so I politely asked the lady if she could move her knees further apart – a question that caused a fair amount of hilarity among the bystanders. She tried, but the restriction remained. I said, “I’m very sorry, but I can’t take you up unless I have full control movement.” She paused and then asked, “Would it help if I took my legs off?” We lifted her back into her wheelchair where she removed her legs before having a thoroughly enjoyable flight along the clifftops of Cornwall. You don’t meet many passengers with removable legs, or the sort of spirit she exhibited.



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