CL60, Almaty Kazakstan, 2007
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On 26 December 2007, a Bombardier CL 604 Challenger being operated by Germany Company Jet Connection Business Flight on a private charter flight from Almaty to Macao took off at night into icing conditions from a 4398m runway which was covered by dry snow and roll control was lost just after beginning rotation. The aircraft wing tip impacted the runway surface and the aircraft subsequently crashed through the perimeter fence, the fuselage broke into three pieces and a fire started. The co pilot was killed and the other three occupants sustained serious injuries.
An Investigation was conducted by the Interstate Aviation Committee with assistance from the accident investigation agencies of the State of the Operator and the State of the Manufacturer. Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) data was available.
The co pilot had been assigned PF duties. It was established that ground de/anti icing with Type II fluid had been completed in accordance with normal procedures and that the aircraft commander had decided that Wing Anti Ice (WAI) should only be selected ‘on’ after take off. However, the Aircraft Flight Manual (AFM) stipulates that in the conditions prevailing for the take off, the wing anti-ice (WAI) system must be ‘on’ but that when Type II, III or IV anti-icing fluids have been applied, the WAI must only be selected ‘on’ just prior to thrust increase for takeoff.
Since FDR data indicated that wing stalled at an angle if attack of between 10° and 10.5°, when the clean wing stalls at about 17° angle of attack indicated the presence of wing surface contamination. It was considered that “most probably, the wing contamination occurred as a result of precipitation in the form of snow sticking to its surface covered with Type 2 anti-icing fluid during the taxiing and at the holding point and line-up position which took altogether about 27 minutes” compared with a prior crew estimate of a HOT of around 30 minutes. It was also considered that “the use of Wing Anti-Ice at takeoff would have provided heating and discharge of the snow stuck to the wing leading edge whose clear surface is critical for the continuous airflow on the supercritical profile wings.”
FDR data also showed that the uncommanded right bank had begun to develop at angles of attack lower than those which would have activated the Stall Protection Warning System.
The Investigation concluded that the accident was caused by:
“the asymmetric lift loss at takeoff which led to aircraft stall right after the liftoff, collision with the ground and obstacles, aircraft destruction and ground fire” and that “the lift loss was most probably caused by the contamination of the wing leading edge with precipitation in the form of snow after the anti-icing which occurred as the crew did not engage the Wing Anti-Ice before the takeoff”
It was also noted that exceeding the AFM limits for rate of rotation when taking off with a contaminated wing could have contributed to the loss of control and that “the inefficiency of the stall protection system at takeoff due to the hypersensitive wing as to contamination of its leading edge cannot completely guarantee prevention of similar accidents in the future”.
Three Safety Recommendations were made as a result of the Investigation:
- Operators of the CL-604 should consider the practicability of:
- - arranging of debriefings to study the causes and contributing factors to this accident;
- - arranging of training for the flight crews operating this aircraft type when preparing for the cold weather period operations concerning the aircraft aerodynamics highlighting the possibility of stall in case of contaminated wing with deposits of ice, snow, frost etc. as well as the de-icing/anti-icing rules and use of Wing Anti-Ice system;
- - recommend that Captains operating ÑL-604 type aircraft with a co-pilot with low (less than 200 hours) experience on this aircraft type conduct takeoffs and landings as PF when there is contamination, precipitation, low braking action, or significant crosswind component.
- Bombardier should consider the practicability of working out more efficient recommendations for pilots to avoid stalling at takeoff due to wing contamination.
- Jet Connection Business Flight should review the content of their “Abbreviated Checklist” in order to avoid the omissions of items stipulated by the manufacturer’s
The Investigation was completed on 6 June 2011 and a ”courtesy” English Language translation of the Final Report  was made available shortly afterwards.