Gremline Flight Safety Report: DA 42 Twin Star Accident on Takeoff

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the gremline digest — one flight, nine decisions, all wrong

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.

 

 

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