Sita D228 at Kathmandu on Sep 28th 2012, bird strike
Last Update: August 26, 2013 / 17:00:52 GMT/Zulu time
Incident Facts
Date of incident
Sep 28, 2012
Classification
Crash
Cause
Bird strike
Aircraft Registration
9N-AHA
Aircraft Type
DORNIER 228
ICAO Type Designator
D228
During level flight phase of the aircraft, the drag on the aircraft was greater than the power available and the aircraft decelerated. That resulted in excessive drag in such critical phase of ascent lowering the required thrust. The investigation was unable to determine the reason for the reduced thrust.
- The flight crew did not maintain the airspeed above the stall speed and there was insufficient height available to recover when the aircraft departed controlled flight.
Contributory Factors
- The flight crew did not maintain V2 during the climb and so the power required to maintain the level flight was greater than it would otherwise have been.
- The flight crew did not maintain the runway centreline which removed the option of landing the aircraft on the runway remaining.
The NAAIC reported the captain (42, ATPL, 8,308 hours total, 7,112 hours on type) was pilot flying, the first officer (24, CPL, 772 hours total, 519 hours on type) was pilot monitoring, when the aircraft was preparing for takeoff from Kathmandu's runway 20 from intersection 2. During line up on runway 20 the commander noticed "there is a bird". The aircraft began takeoff roll, the commander again commented "watch out for the bird", the first officer reported being clear of the bird when the aircraft accelerated through 58 knots IAS. At 70 KIAS the first officer called Vee One, the commander began rotation the aircraft however did not lift off. At 86 KIAS the aircraft lifted off, the gear was immediately retracted, the aircraft climbed to 100 feet AGL over the next 11 seconds, the airspeed however decayed to 77 KIAS, over the next 14 seconds the crew reported a bird strike, the aircraft maintained 100 feet AGL while slowly turning, the speed decayed to 69 KIAS with the stall warning activated at 71 KIAS. The aircraft began to descend slowly, the rate of turn increased rapidly and the aircraft suddenly departed controlled flight, most likely left wing low and impacted an open area about 420 meters southeast of the end of runway 20.
A runway inspection found the remains of the Black Kite on the runway 408 meters down of intersection 2.
A CCTV surveillance camera showed a flash in the area of the right hand engine of the aircraft about 5 seconds prior to the aircraft becoming airborne.
A ground witness, professional pilot, reported that he saw an unsuccessful attempt to rotate the aircraft with the nose gear lifting off the ground and the tail nearly contacting ground, the nose gear lowering but not touching down again before the aircraft rotated again and became airborne.
The NAAIC reported that V1=Vr was 83 KIAS and V2 was 84 KIAS. The "Vee One" call thus occurred premature and below the actual V1, the aircraft thus was not able to become airborne, however, the flight data recorder as well as cockpit voice recorders (by reduction of noise) confirm the Vee One call initiated the takeoff rotation by the commander.
The NAAIC reported that the aircraft was not able to maintain 77 KIAS in level flight suggesting that one engine had failed and the other had suffered a power loss of at least 13%.
The NAAIC reported that the propeller was not found feathered, the blade pitch was at normal operating range, the damage to the propeller blades suggests that the engine had not lost all power but was operating at low power, the damage to the left hand propeller also showed the engine was operating at low power at the time of impact. The power levers found in the cockpit also indicated that none of the engines had been shut down and none of the propellers had been commanded into the feathered position.
No bird remains were found inside the engines, there was evidence however that the Black Kite had been struck by the right hand propeller.
The NAAIC reported that according to the load sheet the aircraft departed with a takeoff mass of 5,834kg and an estimated landing mass of 5,698kg. The load sheet indicated that no luggage had been loaded, surveillance videos however showed luggage of about 80kg was loaded and not removed before the aircraft departed the stand. Thus the takeoff weight was corrected to 5,914kg while using Nepal's standard weights for passengers. Employing European standards for passenger weights the computation arrived at a takeoff weight of 6,148kg above Maximum Takeoff Weight of 6,075kg. The NAAIC subsequently used an assumed aircraft weight of 6,200kg for performance computations.
The NAAIC analysed: "It is possible that the bird momentarily disturbed the air flow into the engine before it was struck by the propeller, causing a surge and the suspected flame seen in the CCTV footage, but the engine manufacturer considered this unlikely. The manufacturer considered that if the bird had been sufficiently close to the air intake to disturb the air flow it would have been sucked in. If the flame seen in the CCTV and accompanying ‘bang’ heard on the CVR were evidence of an engine surge, then another possible cause is a fuel flow problem. However, the manufacturer also commented that this type of engine was very resistant to surge."
The NAAIC analysed based on sound analysis of the cockpit voice recorder and flight data recordings that one of the engines operated at 100% rpm throughout the flight while one engine ran down to 95% rpm and a second time to 91% rpm. The NAAIC analysed that at 95% rpm the drag produced by the propeller exceeded the thrust produced.
The NAAIC analysed further that a grossly overloaded aircraft would have had a better performance than 9N-AHA during the accident flight, hence the overload alone can not explain the performance problem.
The NAAIC continued: "The drag on an engine at flight idle is greater than the drag on an inoperative engine (OEI), and in the case of 9N-AHA where the flight idle fuel flow was incorrectly set too low, the drag would have been even greater at idle (in excess of 350 lb of drag – reference section 1.16.2). It is therefore possible that at about 6,200 kg with one engine at 100% power and one engine at flight idle, there would have been insufficient thrust to maintain 77 kt, and the additional drag on one side would have affected controllability more than in the OEI case."
The NAAIC stated in the analysis, that the power loss began at about 70 KIAS and further analysed, that a power loss below V1 (83 KIAS) should have triggered a rejected takeoff. The bird impact occurred at about the time of the premature Vee One call by the first officer at 70 KIAS, there is no evidence to suggest that the crew detected a power loss while the aircraft was still on the ground, the aircraft initially still accelerated though at a lower rate than during previous takeoffs, became airborne at 86 KIAS above V2 and continued to accelerate for about 2 seconds, only then the speed began to continuously decay. The NAAIC said: "There was no evidence to suggest that the flight crew recognised that a power loss had occurred on the ground, possibly because it occurred gradually and progressively rather than instantaneously. This would account for why the takeoff was continued."
The NAAIC analysed: "For an engine malfunction that occurs on takeoff at or above V1, the POH allows flight crews to continue the takeoff or land back on the runway should it be long enough to safely bring the aircraft to a stop. There was probably between 2,500 and 3,000 ft of runway available ahead of the aircraft which should have been sufficient to bring the aircraft to a halt but the flight crew did not select this option. One reason the commander might have decided not to land was because company policy is that the takeoff should be continued for an engine malfunction at or above V1."
The NAAIC analysed: "The actual weight of passengers and baggage on board is unknown. However, it is feasible that the passengers weighed more than was recorded ... In the worst case, the TOW could have been 6,168 kg which would also have been above the higher, WAT-limited, MTOW of 6,075 kg and, in this case, takeoff performance might have been compromised."
In summary the NAAIC analysed: "No faults were found with either of the engines, there was no evidence of a bird ingestion into the engine. Both engines were producing low power at impact, both propellers were in their normal operating range. However, an insideous power reduction occurred starting at 70 KIAS which went unnoticed by the crew. Following lift off the pitch attitude was set too high for the aircraft to maintain V2, the aircraft's speed fell below V2 requiring more thrust than available to accelerate again.
The NAAIC concluded the analysis: "The investigation was unable to determine the cause of the thrust reduction."
Incident Facts
Date of incident
Sep 28, 2012
Classification
Crash
Cause
Bird strike
Aircraft Registration
9N-AHA
Aircraft Type
DORNIER 228
ICAO Type Designator
D228
This article is published under license from Avherald.com. © of text by Avherald.com.
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