The approach controller at Nagoya, Japan, cleared Dynasty 140 for a visual approach to Runway 34. Weather conditions consisted of scattered clouds at 3,000 feet, and the visibility was greater than 10 miles. The crew of the China Airlines Airbus A300-600 had the runway lights in sight. The first officer was hand-flying the airplane, and it appeared that another night flight was about to end routinely.
In the vicinity of the outer marker, the first officer inadvertently activated the go-around switch. This caused the throttles to automatically and obediently move forward. The engines of the Airbus are slung beneath the wings, and the increased engine thrust caused the nose to pitch up. The Airbus rose above the glideslope.
The captain was surprised by this turn of events and said to the first officer, "You activated the go [-around] lever!"
The most conservative action at this point would have been for the crew to accept and continue the go-around, circle the airport, and begin a new approach. Or the pilots could have disengaged the autothrottles, lowered the nose slightly to recapture the glideslope, and continued the approach manually as if nothing had happened. Instead, the first officer (or possibly the captain) engaged the autopilot. Because the autoflight computer was still in the go-around mode, the autopilot responded by raising the nose of airplane with aggressive authority. It had been programmed to execute a missed approach, and that is exactly what it was going to do.
At this point the crew probably should have allowed the autopilot to have its way and continue the missed approach. Another choice would have been for either pilot to disengage the autopilot and continue the approach manually. But the crew did neither. With the autopilot controlling and apparently in command of the aircraft, the first officer and then the captain pushed forward on their control wheels in an effort to force the nose down and recapture the glideslope.
But the autopilot was tenacious and continued its attempt to execute a go-around. It also added nose-up trim to counter the pilots' contrary efforts. The harder the pilots pushed, the more the autopilot moved the trimable horizontal stabilizer (similar to that on a Cessna Skywagon) in the opposite direction. Eventually the stabilizer reached its maximum nose-up-trim position.
After the autopilot had been at work for an agonizing 31 seconds, the captain finally depressed the switch on his control wheel and disengaged the autopilot. But by this time it was virtually impossible for him to hold the nose down. (For reasons that cannot be explained, neither pilot used the thumb-operated trim switch on each control wheel to reposition the horizontal stabilizer in a nose-down position.)
At less than 600 feet agl, the captain finally recognized that the landing attempt should be aborted and reactivated the go-around mode. This resulted in the reapplication of full power, which further increased the strong, nose-up pitching moment. The aircraft began an enthusiastic climb during which it achieved a pitch attitude of 53 degrees and indicated airspeed decayed to less than 75 knots.
The rest was predictable. The Airbus stalled, pitch-ed down sharply, and hit the ground nose-first. The aircraft burned and was destroyed. Miraculously, seven of the 271 people aboard the flight survived.
The Japanese Ministry of Transport determined that numerous factors were responsible for this tragedy. One of the most obvious was that the pilots did not understand or operate the autoflight system (the two autopilots and their related computers) in accordance with instructions and warnings in the aircraft flight manual.
Although it is tempting to be a Monday-morning quarterback and criticize the crew for its failures, we should instead make better use of the lessons learned by asking ourselves how well we understand the systems in the aircraft that we fly and how prepared we are to deal with their idiosyncrasies.
During many years of administering flight reviews, I have noticed one glaring failure on the part of virtually every pilot with whom I have flown. Rarely, if ever, do they perform an operational check of their autopilots during the preflight runup. (Before you accuse me of being holier than thou, I confess to being equally careless in this regard.) It became obvious to me that most of those who fly aircraft with autopilots not only do not know how to perform a preflight check of their autoflight systems, most do not even know that such a procedure exists. (It usually can be found in a supplement to the pilot's operating handbook.)
Curiously, an instructor checking out a pilot in an aircraft with an autopilot seldom covers this subject, perhaps because he, too, has failed to learn and understand the applicable material in the POH.
Autopilots are reliable, and we seem to take them for granted. Too few of us understand how and why they can go awry, the warnings they provide, what happens during an attempted override, and what other methods are available to disable the system when the primary disengage switch fails to operate as advertised.
Above all, it is important to be aware that an autopilot can automatically take the unprepared pilot to his demise.
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