One
Flight, Nine Decisions, All Wrong
A 47 year-old pilot with 1315 hours total and 62 hours on type planned to
fly a DA 42 Twin Star aircraft powered by two Thielert TAE 125-02-99 diesel
engines to Lands End Aerodrome in January 2009. He had two passengers for the
flight. He telephoned Lands End ATC prior to departure and was advised
against attempting the trip due to bad weather at Lands End. However, he took
off as planned and used the aircraft weather mapping system to avoid bad
weather en route.
The
weather at Lands End had improved by the time the aircraft arrived there and
the aircraft landed on Runway 25.
Lands End Aerodrome has two main and two subsidiary grass runways.
The main runways are 07/25 and 17/35. Runway 25 normally has a declared Take
Off Run Available (TORA) of 695 m with a displaced threshold and with a drop
of 32 m along its length, giving a downhill gradient of 4.6%. A NOTAM was
issued from Lands End at 1000 hrs UTC on the day of the accident which
further displaced the threshold of Runway 25 due to soft ground, reducing the
TORA to 574 m.
The pilot noticed that the airfield grass surface was very wet,
particularly around the hard standing area by ATC where he was instructed to
park.
When the
pilot returned to the aircraft for departure from Lands End he noticed that
the left engine oil quantity was low and added about one quart of oil. He
then started the engines and carried out power checks without noticing any
problems. The aircraft became bogged down soon after leaving the hard
standing area. The pilot used full power in an attempt to extract the
aircraft but this failed and he shut down. An Airport Fire Service (AFS)
vehicle towed the aircraft back to the hard standing area and the AFS crew
washed the landing gear to remove the mud accumulated during the pilot’s
attempt to taxi the aircraft after it had become bogged down.
Having performed several engine starts the pilot was aware of a “L
ECU A FAIL” caption illuminating on the Primary Flight Display indicating a
failure in the left engine control system. The engines and propellers of the
DA 42 are controlled by a dual channel digital Engine Control Unit (ECU).
This electronically controls the manifold pressure, fuel rail pressure (which
determines the quantity of fuel injected) and the propeller speed according
to the power lever position. The engine is normally controlled and regulated
by Channel A of the ECU. However, if a failure is detected then Channel B automatically
takes control. The ECU also records fault information in an ‘event log’ and
time history at one second intervals for various engine parameters. Engine
parameters, including propeller speed and engine load are displayed on a
central Multi Functional Display (MFD) in the cockpit. The Primary Flight
Display (PFD) displays the crew alerting (annunciator) system in addition to
air data, altitude and heading information. A warning or caution annunciator
will flash on the PFD accompanied by an aural tone. A warning is accompanied
by a repeating tone and a caution is accompanied by a single tone. In the
case of minor faults the annunciator can be reset once by pressing the ECU
TEST button for more than 2 seconds. However, the annunciation will re-appear
upon the next attempt to start the engine.
A download of the fault information and time
history from both ECUs, supplied to the engine manufacturer by the AAIB,
provided the following interpretation of subsequent events.
There were no faults recorded by the right
engine ECU. The data from the left engine ECU indicated that the engine was
shut down at 1119 hrs with Channel A active and no faults recorded. The first
warnings were recorded at around 1202 hrs when oil temperature, coolant
temperature, outside air temperature, oil pressure, fuel rail pressure and
gearbox temperature sensor failures were detected. These sensor failures
would result in a flashing L ECU A caution. The engine was started at 1357
hrs and since the ‘health’ of Channel A was lower than that of Channel B,
control of the engine automatically passed to Channel B.
The engine was restarted with Channel B in control. The ECU test
button was reset, which should have resulted in the flashing L ECU A FAIL
caution becoming steady. There were various resets and engine restarts, all
of which would have resulted in a steady L ECU A caution.
At 1450 hrs the final takeoff attempt began with the left engine ECU
Channel B in control. A steady L ECU A caution would have been illuminated.
The data shows an increase of power on both engines to maximum for 28 seconds
before the power decreased and both engine speeds reduced to zero. Both ECUs
continued to record information until the battery became depleted.
The DA 42
Flight Manual Abnormal Operating Procedures following an ECU fail caption
states:
”L/R ECU
A FAIL
(a) ‘ECU A’ caution on ground
-Terminate flight preparation
(b) ‘ECU A’ caution during flight
NOTE
In case of a failure on the
electronic ECU (Engine Control Unit) ‘A’ the system automatically switches to
ECU ‘B’
1. Press the
ECU TEST button for more than 2 seconds to reset the caution message.
if ECU A caution message reappears, or cannot be
reset;
2. Land on the nearest suitable
airfield.
3. The engine must be serviced after
landing
if ECU A caution message can be reset
2. Continue flight.
3. The engine must be serviced after
landing.”
Despite
these warnings, the pilot decided to continue his attempt to depart from
Lands End Aerodrome. He started both engines and taxied across the airfield
to line up on Runway 25. From the wheel tracks on the runway this would have
given a runway distance remaining of 465 m for the takeoff.
CAA Safety Sense Leaflet 7c “Aeroplane Performance” strongly
recommends that the appropriate Public Transport factor should be applied to
all flights. For take-offs this factor is x1.33 and applies to all
single-engined aeroplanes and to multi-engined aeroplanes with limited
performance scheduling (Group E). The leaflet also specifies further
cumulative factors that should be applied in certain circumstances, including
an increase of 25% on soft ground. Had the pilot applied these safety factors
he would have arrived at a take-off run required of 977m in the conditions at
the time of the accident. This figure is more than twice the actual Take Off
Run Available on Runway 25 from where the pilot planned to make his first
take-off attempt.
As the power was increased to begin the take-off roll the aircraft
immediately became bogged down again, so the pilot shut down the engines. The
AFS then towed the aircraft to the right side of Runway 25, adjacent to the
normal threshold. The pilot then restarted the engines and planned to
take-off by tracking parallel to Runway 25, displaced onto what the pilot
thought was firmer ground. The aircraft accelerated as power was increased
and the pilot closely monitored the airspeed, hoping to reach 70 kt to be
able to lift off. However, at around 46 kt he reported a “pull to the left”
and became aware of the “L ECU A FAIL” caption being illuminated. He retarded
the throttles and aborted the take-off.
The wheel marks on the airfield indicated that the aircraft had
followed a straight track in a direction of 200 degrees from the start of the
attempt, some 50 degrees off runway heading. This straight track continued
until the aircraft struck the airfield boundary hedge after a ground roll of
some 350 m. The aircraft immediately nosed over in very soft ground and came
to rest inverted. The AFS attended the scene of the crash and assisted the
pilot and both passengers from the wreckage. All three suffered minor
injuries. There was no fire.
The recorded information indicated that both engines developed full
power during the last attempted take-off.
CAA Safety
Leaflet 23 “Pilot’s it’s Your Decision” discusses issues surrounding the
decision making process with regard to flying. The pilot stated that it was a
wrong decision to attempt a take-off at all and concluded that he would not
be operating a DA 42 from a wet grass surface again.
The facts related above are closely based on AAIB Field Investigation
Report EW/C2009/01/06 which source is gratefully acknowledged. The following
comments do not seek to reflect the views of AAIB or of the CAA and are those
of the Gremline Technical Editor.
This pilot seems to have been determined to have an accident somewhere
along the line between the time he decided to ignore the advice from Lands
End ATC before he began the flight until, after several false starts, he
drove his aircraft into the boundary hedge in a futile attempt at a take off
that could never have been conducted safely.
Other pilots are invited to sift through this Report and see how many
wrong decisions this pilot made on this one flight. He and his passengers
were very lucky to survive. If the only lesson this pilot learnt was not to
operate a DA 42 from wet grass I believe he missed many more important
lessons. Aircraft don’t cause accidents, people do.
It is better to learn from the mistakes of others rather than
to make them all oneself.
Text and Photographs © 2009 Gremline & Hill House
Publications, unless otherwise stated.
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