Accident Sequence
The aircraft departed Kathmandu-Tribhuvan Airport on a ferry flight to Pokhara for a C-check maintenance program. On board were technical engineers and staff of the airline. At 05:25:55, the aircraft rotated near 120 knots computed airspeed. It achieved a pitch up of 13 degrees within 4 seconds (15 degrees in 6 seconds) at a maximum calculated pitch rate of 8.6 degrees per second. The aircraft then rolled 26 degrees right at a maximum calculated roll rate of 15.5 degrees per second. During this period, the stick shaker activated on both sides for 4 seconds, coinciding with an unidentified GPWS audio message. The fuselage angle of attack recorded 6.9 degrees.
From 05:26:01 to 05:26:05, the aircraft rolled left up to 55 degrees at a recorded roll rate of 36.6 degrees per second. The pitch remained approximately 15 degrees nose up, ground speed steady around 147 knots, and radio height increased to 77 feet. The stick shaker deactivated for 1 second, then reactivated for 2 seconds, correlating with another GPWS audio message. The stick pusher activated on both sides during the second stick shaker activation, followed by a pitch down and a GPWS Pull Up message.
At approximately 05:26:05, the aircraft rolled right reaching 94.6 degrees at a maximum roll rate of 56.1 degrees per second. The pitch increased to 19 degrees, then decreased to 2 degrees. The heading changed by 12 degrees during the takeoff. Vertical acceleration ranged from 0.40G to 1.69G, and lateral acceleration peaked at 1.54G.
Impact and Aftermath
The final recorded radio height was 63 feet during a roll of 30 degrees right, with pitch between -3 and 1 degree. The speed was 142 knots computed airspeed, and the fuselage angle of attack reached 8 to 12 degrees. The last recorded location was approximately 6100 feet from the threshold of runway 02, near taxiway Juliet. The aircraft impacted terrain east of the runway at coordinates 27°42’3’’ North and 85°21’42’’ East, with the right wing making first contact. The impact trail extended about 1000 feet east of the runway. The captain was seriously injured, and 18 other occupants were killed.
Probable Cause
The most probable cause of the accident was a deep stall during take-off because of an abnormally rapid pitch rate commanded at a lower than optimal rotation speed. The following contributory factors were identified: - Incorrect speeds calculated based on erroneous speedcard. The interpolated speedcard of the operator for 18,500 kg TOW mentions incorrect V-speeds for take-off. This error in the speedcard went unnoticed since its development. There was no acceptance/approval of the speedcard booklet. - Failure to identify and address multiple previous events of high pitch rate during take-off by the operator. - The operator showed gross negligence in complying with the prevailing practices of ferry flight planning, preparation and execution. There is a lack of consistent definition of ferry flights. - Gross negligence and non-compliance by the operator during the entire process of cargo and baggage handling (weighing, loading, distribution and latching), while violating the provisions of operational manual and ground handling manual. The load was not adequately secured with straps, tie-downs, or nets, while the flight preparation was rushed.