Wednesday, July 17, 2013

Asiana 214 Has Automation Trumped Airmanship?

Asiana 214,  the 777 that crashed at San Francisco last week, came in too low and too slow, and hit the seawall at the end of the runway.  Apparently the crew had set the autothrottle to hold the proper airspeed (137 knots) and for some reason the autothrottle allowed the airspeed to slack off too much.   The crew didn't notice until it was too late.
    They haven't said if the autothrottle failed, or wasn't set correctly, or for some software reason decided not to hold the setting.  The Aviation Week article goes into some detail about the various modes of the autothrottle, in some modes, it doesn't work the throttles, and it can change modes on its own without notifying the pilot.
   Autothrottle is a new fangled luxury.  Back in my day, only the C141 jet transport had autothrottle, and that was part of the All Weather Landing System, unique to the C141.  All the other aircraft had a plain old throttle lever, the engine power stayed where it was set by hand.  And they all managed to land in one piece.

    Speed on landing approach is critical.  You want to come in as slow as possible.  Slow makes it easier to get the wheels on the runway (as opposed to in the weeds), easier to get the plane stopped before running off the far end of the runway, and  lessens the shock on gear and airframe.  Too much shock breaks things and blows tires.
  On the other hand, go too slow and the wing stalls, stops producing lift, and the aircraft falls like a stone.  All control is lost.  There is little difference between proper landing speed and stall speed.
   It's hard to understand how the crew failed to check their approach speed, and notice that the autothrottle was playing them false.  For that matter it's hard to understand why they used autothrottle at all.  Was it me, with few hours in the 777, I'd  tend to do things by hand, the old fashioned way, rather than find out what nasty bugs might lurk in a tricky newfangled autothrottle.

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