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I'm trying to track down a story about an incident involving an Airbus airplane my father told me about 25 years ago, when he was working at a Boeing supplier.

Reportedly, what happened was the airplane's autopilot was set to bring them in to a certain airport, and the pilots noticed that it was descending too early. So, they took over the controls, lined up manually, and at about a hundred feet up, the autopilot wouldn't let them descend further. So, they did a go-around, tried the approach again, and the same thing happened. At this point, they diverted to another airport and landed without incident. Turned out that the airplane's database had an incorrect position for their destination: the plane thought they were overshooting the runway, and wouldn't let them perform what it saw was an off-airport landing.

Was this based on an actual incident, or just one of the "Airbus airplanes don't let the pilot fly" stories circulating among Airbus competitors?

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never heard of such accident nor such capability of the airbus autopilot. I put my chips on the second hypothesis. –  Federico Jun 17 at 10:38
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If you find a notable reference for this story, it being retold on a website or in a book, then its a good fit for skeptics.stackexchange.com –  Jamiec Jun 17 at 12:38
    
I'd say this must be an urban legend. Not sure if it was like this everywhere, but 25 years ago, there existed a rule for safety critical systems, that any kind of automation was only allowed if it could be shut down completely by a human. Note that it's not more like this nowadays. –  Zane Jun 17 at 13:41
    
@Zane, not anymore? got any links/documents to support the claim? –  Federico Jun 17 at 14:22
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@voretaq7: No, it didn't. The aircraft didn't start to climb because it didn't have sufficient speed for it. The computer did prevent pulling up further, but if it didn't the aircraft would have stalled with the same overall result. They were simply too late applying power (which the computer would have done for them much earlier if they didn't disable it!!) and nothing could have saved them at that moment. –  Jan Hudec Jun 17 at 16:55

1 Answer 1

up vote 21 down vote accepted

I believe this is a hoax1. I've read through several documents describing the protections provided by Airbus flight laws (this is not autopilot; autopilot is a separate layer on top of it) and have never seen any mention of any kind of ground proximity protection. Only standard (E)GPWS which yells "terrain, pull up".

Update: Of course now there is EGPWS that gets aircraft position from GPS and can yell "terrain, pull up" when there is no airport ahead, but 25 years ago there was only GPWS based on radar altimeter which didn't know anything about position and would switch to simply read out2 the radar altimeter value whenever gear (and maybe also flaps; not sure here) was extended.

1Might have been even attempt at FUD against the then novel technology.

2That is say "one thousand", "five hundred", "two hundred", "one hundred", "fifty", "fourty", "thirty", "twenty", "retard"3 (and "ten" or "five" when it stops saying "retard" and the wheels are not on the ground yet). This is useful during approach so the pilot can concentrate less on the instruments and more on outside reference and in the final phase to help judge when flare should be initiated. It will also warn "sink rate" when the sink rate is excessive (more than -1000 ft/min, the stabilized approach criteria).

3At 15 or so feet, if the thrust levers are not in idle gate, the Airbus system starts announcing "retard" and keeps announcing it until the thrust levers are placed in the idle gate (or reverse). This is specific to Airbus. I believe it can also announce "minimums" when approach minima are configured in the flight management system.

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