The final report into Indonesia’s Air Asia Flight QZ8501 from Surabaya, Indonesia to Singapore highlighted a lack of “decisive” control from the aircraft’s captain as the reason to why the Airbus A320-200 stalled 11 miles over the Java Sea.
The crash occurred on December 28, 2014, around five years after the Air France AF447 accident, which left the entire industry stunned after the report highlighted the highly experienced crew was unaware that their aircraft was in a stall.
On December 1, 2015, Indonesia’s NTSC realized their final report showed the contributing factors to the crash.
It was discovered that the cracking of a solder joint on a piece of electrical equipment connected with the Rudder Travel Limiter Unit, or RTLU, resulted in a loss of electrical continuity and led to the RTLU failure. This failure occurred four times during the flight. Following the first three failures, in accordance with the Electronic Centralized Aircraft Monitor messages, the crew worked relevant checklists to resolve the issue, which included the resetting of the circuit-breakers. The investigators highlighted that some of the circuit-breakers, including the ones that directly affect the aircraft’s autopilot system, could only be reached by a crew member outside of their seat.
Following the circuit-breaker reset, the autopilot disengaged and led to a sudden roll. The pilot flying, the first officer, had taken 9 seconds to react to the unusual attitude and attempted to correct the roll with strong control inputs to the side-stick. Such movements included the side-stick being pulled back, pulling their aircraft’s nose up, and initiating a climb. Following the climb, the airspeed quickly decayed and the aircraft entered a stall. The flight data recorder featured a control input from the captain’s side-stick only after the stall warning had sounded twice. More so, the cockpit voice recorder revealed that no control “handover” was verbally exchanged between the first officer and the captain, but the conversation between the two indicated that the captain assumed the role with no formal announcement.
Following this confusion over who was in control, the captain was pushing the side-stick forward, to lower the nose and recover from the stall, while on the other hand, the first officer was pulling the side-stick back to raise the nose. Because Airbus’ flight-control logic acted on the sum of two side-stick inputs, both crew members’ actions were effectively cancelling each other’s out. The captain did not activate the priority mechanism, which would have given his side-stick absolute control of the aircraft. The mechanism requires the captain to hold down the take-over button for at least 40 seconds, but the FDR showed that the captain’s button was pushed twice, for a period of 2 seconds and 5 seconds respectively.
From the flying perspective, these events highlight, again, that as well as a lack of proper communication between the crew, the airmanship of neither crew was good enough to overcome the problem they were presented with. Airplanes fly on the autopilot systems for hours at a time, which is entrusted with the delicate balancing act of handling the airplane at such cruise altitudes and speeds. Yet when it comes to basic flying skills, as seen with the AF447 flight, the crew were unable to recover from the basic stall.
Pilots are trained from all stages of licences about the stall and the recovery. It is a legal minimum that two hours of stalling is acquired for the EASA Private Pilots Licence, for example. At Commercial Pilot Licence level, stalling is practiced over and over again, and not just the basic stall. Stalling with full flap, as well as with approach flap in a banked aircraft, are also practiced, with the basic recovery of lowering the nose, applying power and reducing height loss: the fundamental skill of recovering from a stall.
Following AF447, flight schools have tweaked their syllabuses to include more stall training as well as unusual attitude recovery. There is not much more teaching that can be done to prevent such disasters happening again, yet, we are here with the same fundamental cause to the crash as we saw with AF447 five years ago.
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