Investigators have been unable to determine precisely why a Kazakh Bombardier CRJ200 crashed while attempting a go-around at Almaty two years ago, with the loss of all 21 on board.
Analysis of the aircraft’s dynamics shows that, instead of climbing away from the approach to runway 23R, it dived from a height of about 150m (500ft), striking the ground and disintegrating.
“It has not been possible to clearly identify the reason for the aircraft’s transition to a dive – instead of a climb – from the available data,” says Russia’s Interstate Aviation Committee.
The inquiry points out that the aircraft descended after its elevators deflected into the nose-down position.
But it says there was no evidence of technical failure on the SCAT aircraft nor any indication that the jet was affected by icing, windshear or wake turbulence.
The CRJ200 had been attempting to land in poor visibility following a service from Kokshetau on 29 January 2013.
While flight data shows the aircraft was stable on its approach, the cockpit-voice recorder indicates that the captain was extremely frustrated by the weather conditions at Almaty, which he had hoped would improve before the arrival.
The inquiry says that, although the aircraft continued on its approach, the cockpit recordings show that there was no intention to pursue a landing below minima, and the captain called for a go-around.
Fifteen seconds before impact, at a height of 180m, the autopilot was disengaged, when the aircraft was flying at 140kt and descending at around 600-800ft/min. Its flaps started retracting while the engines’ thrust increased.
But just 4s after the autopilot disconnection the elevator began deflecting into the pitch-down regime. An automated call-out told the crew that the CRJ200 was at 500ft and the airspeed increased to 150kt.
The horizontal stabiliser’s position remained unchanged but the aircraft pitched increasingly nose-down.
“Despite the increase in airspeed and [descent] the crew did not take action to put [the aircraft] into a climb,” says the inquiry.
Less than 5s after the aircraft entered the dive its ground-proximity warning system cautioned on the sink rate and then began issuing urgent terrain alerts, instructing the pilots to pull up.
But the aircraft’s pitch continued to deteriorate, exceeding 20° nose-down, an attitude from which the CRJ failed to recover. It struck the ground about 1.6km before the threshold of 23R.
Bombardier modelled the last 30s of the ill-fated flight as part of the effort to explain the accident. The simulations revealed nothing unusual in the aircraft’s aerodynamic behaviour, and that it had responded as designed to the elevator deflection. There were “no other external factors” contributing to the downward pitch, says the inquiry.
It states that, in the absence of any system failure, the elevator deflection could have resulted from control inputs by the crew.
The inquiry has struggled to resolve the mystery, saying that there is “no logical reason” for the initiation of the fatal dive when the aircraft should have been climbing for the missed approach.
Investigators have considered the possibility of somatogravic illusion – a strong but false perception of the aircraft’s pitch. But the flight-data recorder revealed slight changes in the CRJ’s elevator deflection during the dive which, the inquiry claims, are not characteristic of the effects of the illusion.
Spatial disorientation has also been put forward but the inquiry suggests that the captain’s experience – more than 18,000h including 1,000h on the CRJ – does not support this theory.
Source: Cirium Dashboard