[Ref Flight International Magazine 14-20 Jan 2020]
Bek Air is still pushing its theory that wake turbulence contributed to the loss of a Fokker 100 on 27 December accident, which resulted in 12 fatalities.
It appears to show the ailerons, rudder and elevators were active during rotation, as the aircraft experienced lateral and longitudinal instability during the brief period it was fully airborne.
Some of the data – such as the airspeed – is discontinuous, suggesting it has been sourced only after the jet lifted off, while other information, like sudden changes in wind speed and direction, is likely to be unreliable because the aircraft, having descended back to the ground, subsequently travelled at an unusual attitude, barely above the terrain.
After the aircraft lost height, the data suggests thrust on both Rolls-Royce Tay engines simultaneously reduced for around 10s before increasing to a higher level than before the power dip.
Bek Air has acknowledged the surveillance video showing the de-icing of the aircraft’s horizontal stabiliser, but the video does not indicate any de-icing of the wings.
The airline has also released a document on de-icing fluid hold-over times, which appears to highlight a figure of 45min for Type I fluid in frost below -10°C (14°F). Such fluids are not particularly viscous and are intended for short-term use.
Meanwhile, air navigation service Kazaeronavigatsia has already insisted that the 2min interval between the Fokker 100’s departure and that of a preceding aircraft was sufficient for wake vortex separation.
Russian and Kazakh investigators have yet to disclose any formal information of the accident sequence.