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.
Text and Photographs © 2009 Gremline & Hill House
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