FlyDubai Flight 981: Bad Weather + Somatogravic Illusion = Deadly Combination
When the final report was released it cited that pilot error and possible crew disorientation were the primary causes of the FlyDubai flight 981 accident. Looking more deeply into how the aircraft was configured that night, may be able to provide some clarity as to why the flight crew acted in the manner they did.
Firstly, since weather conditions were very poor the aircraft was placed in a holding pattern for over an hour hoping that the conditions would improve before another attempt could be made at landing. Since the aircraft was holding, more fuel was being burned to an already lightly loaded aircraft. Furthermore, it wasn't carrying any cargo and since it was a ‘red-eye’ flight, the aircraft only filled one third of its seating capacity. This led to the overall weight of the aircraft being significantly low.
Relating this to the Fly Dubai 981, upon the second attempted landing, as the aircraft initiated the ‘go-around,’ full thrust could have caused a low weight aircraft to significantly pitch up since the thrust to weight ratio would have been high. It’s this sudden pitch up of attitude that could have disorientated the pilots; add bad weather to this mix and you have a compelling argument that the PIC succumbed to Somatogravic Illusion.
The flight data recorder showed that when the flight crew applied full power there was a moment when the PIC pushed the control wheel down. This makes sense as maybe the PIC was preventing a possible stall indication from occurring as the aircraft's angle of attack rose. However moments later, the PIC’s flight inputs were erratic, pushing the aircraft into a nose down, ‘dive,’ situation. Frighteningly, two years prior Tatarstan Flight 363 approached to land in Russia in similarly poor weather conditions, initiated a ‘go-around’ but ended up nose diving, killing all those on board.
It’s important to understand that sensory information is determined by our vestibular system. Inside the inner ear we have hairs that sense motion by bending forwards and backwards. Figure 1 shows this through the use of the white hairs. When the hairs are standing upright we perceive this as our body is level. However, during an acceleration (i.e a ‘go-around’) the hairs are bent backward even if the body is upright, in a flight deck we perceive this to falsely indicate that the aircraft is pitching up.
FlyDubai flight 981 was flying in a layer of thick cloud and therefore had no visual cues to rely on. Even glancing away from the instruments for just one moment could lead to the pilot’s sensory system taking over. I cannot stress enough, how important it is always to rely on your flight instruments.
Whilst the aircraft was placed in the holding pattern the flight crew contacted the Fly Dubai Control Centre over concerns that the crew would exceed their operational limit of flying for that day. Moreover, with the weather conditions refusing to get better they pondered diverting to an alternate airport. The FlyDubai control centre told the flight crew that although another attempt at landing would be preferable it's ultimately their choice. The crew had been flying for nearly 8 hours, which is close to the operational limit for that flight. In addition, whether fatigue played a role in their decision to attempt another landing at Rostov-On-Don aerodrome is questionable. In hindsight their decisions to divert to an alternate airport with better weather conditions may have been the wiser choice.
Soejatman, G. (2016) ‘ADS-B Analysis of FlyDubai 981: A Case of Somatogravic Illusion?’, Gerry Airways, p. 1. Available at: http://www.gerryairways.com/index.php/en/safety/ads-b-analysis-of-flydubai-981-a-case-of-somatogravic-illusion/.Accident,
A. I. R. and Commission, I. (2016) ‘This document is an English translation of the Final Report on the accident involving the Boeing 737-8KN aircraft registered A6-FDN that occurred on March 19 , 2016 ( 00 : 42 UTC ) at Rostov-on-Don aerodrome Date and time’, 2016. Available at: https://www.flightradar24.com/blog/wp-content/uploads/2019/11/report_a6-fdn_eng.pdf.
Martin, S. (2019) ‘This Illusion Can Easily Lead To A Crash’, BoldMethod, p. 1. Available at: https://www.boldmethod.com/learn-to-fly/aeromedical-factors/the-somatogravic-illusion-causes-accidents-how-to-prevent-it/.
Wise, J. (2016) ‘An Illusion Made FlyDubai Pilots Crash Their Plane Into the Ground’, Popular Mechanics, p. 1. Available at: https://www.popularmechanics.com/flight/a20530/flydubai-pilots-crash-illusion/.
Marrow, A. (2019) ‘Report cites pilot error in 2016 Flydubai plane crash in Russia’, Reuters, p. 1. Available at: https://www.reuters.com/article/us-russia-crash-flydubai/report-cites-pilot-error-in-2016-flydubai-plane-crash-in-russia-idUSKBN1Y01QD.