Once again, a highly sophisticated airliner piloted by a professional crew has plummeted to its doom largely because of the crew’s failure to recognize and properly recover from an aerodynamic stall.
This time it was AirAsia Flight 8501, an Airbus A320 that crashed into the Java Sea in December 2014. In a recent report on the accident, the circumstances were painfully similar to the 2009 crash of Air France Flight 447, a widebody A330, which crashed in similar fashion on the other side of the world. That accident has become somewhat of a poster child of what not to do in the event of a high-altitude stall.
In the case of AirAsia and nearly all of these types of disasters, there was a chain of events and confusion that led to the crash, but in the end, there was nobody minding the store or recognizing that the airplane was out of trim—and, later, climbing at an unsustainable rate.
Starting the chain was a failure of the rudder travel limiter. This occurred four times in 15 minutes, and it undoubtedly would be frustrating to the pilots to go through the reset procedures and not have them work. The airplane had a history with this issue. After the final occurrence, the pilots shut down both flight augmentation computers (FACs), which disconnected the autopilot and autothrottles, and placed the Airbus in a degraded level of automation known as alternate law. In alternate law, the Airbus loses envelope protection and can be stalled, whereas in normal law it can’t.
Once the FACs were turned off, the rudder parked itself in a two-degree left deflection, a significant amount at cruise speed. Apparently, the pilots didn’t notice and correct this yaw. With that rudder deflection, the airplane rolled (six degrees per second for nine seconds), reaching 54 degrees of bank before any correction was input by the first officer, the pilot flying. Initially, the pilot brought the wings nearly level with the sidestick (ailerons and spoiler), but then he increased bank again and pitched up abruptly. The Airbus climbed from 32,000 feet to 38,000 feet at a maximum rate of 11,000 feet per minute.
Since the airplane was in alternate law and no Transport jet can sustain that rate of climb for any length of time, it’s no surprise that the airplane stalled. The audible stall warning continued nearly the entire ride down to the sea, with the airplane pitched up some 40 degrees.
During the struggle for control, the captain, who may have been out of his seat attempting to reset the FAC circuit breakers, instructed the first officer to “pull down,” a command both nonsensical and confusing. The captain was Indonesian and the first officer French, which didn’t help crew communication.
Further adding to potential confusion is the Airbus design, in which the sidestick controllers are not interconnected. The captain may not have known that the first officer was holding his stick back, since they are not mechanically linked. This also was a factor in the Air France crash.
All manner of speculation can come from this report, and I don’t want to stomp on the graves of these pilots, having not been there myself. They faced distraction and confusion, and had communication issues. But throughout the event there was clearly a loss of situational awareness of the airplane’s state. And, unlike the Air France tragedy, these pilots had operating airspeed indicators.
Is this another accident that can be blamed on pilots’ addiction to automation? Have we been so removed from basic flying tasks that when the automation quits, we can’t take over the flying duties? I discussed this in an August 2014 column (“Career Pilot: What Happened to Stick and Rudder Skills?”) and came to the conclusion that pilots who learn to fly in simulators instead of real airplanes may never develop the proper seat-of-the-pants feel for flying an airplane without automation. Of course, there’s more to the story than just basic flying skills, and I encourage readers to reference the accident report. Emergency checklist discipline also appears to have been lacking in the cockpit, among many other findings.
Finally, Air France 447 was a sort of wake-up call to the industry, leading many airlines, including mine, to incorporate high-altitude upsets into recurrent simulator training. Apparently, AirAsia did not, and that’s unfortunate as I found that training to be very enlightening.
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