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Has there ever been an uncommanded lowering of the landing gear on a large commercial jet? I could not find any instance of it in a preliminary google search. Could a simple short-circuit cause such a thing?

I think this would actually be pretty bad at cruising conditions, because the airplane is going much faster up there, than on approach. But the air is also much thinner so I can't be sure.

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  • $\begingroup$ IIRC (so take this with a large handful of salt), jetliners cruise at something like 300-400 KIAS, and land at maybe 100-120 KIAS. Since it's indicated airspeed that would be of interest here, it stands to reason that lowering of the landing gear would still be much worse in cruise than near landing. $\endgroup$ – a CVn May 27 '18 at 14:29
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    $\begingroup$ @MichaelKjörling, I am rather confident jetliners cruise below 300 KIAS. The Vmo is usually 320 or 330 knots indicated, but the Mmo becomes the limit above around FL270 and pushes it below 300 knots indicated. $\endgroup$ – Jan Hudec May 27 '18 at 22:24
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    $\begingroup$ @JanHudec Yes, very much so. High 30's for a typical cruise altitude, Mach .78 ballpark for a 737, you could have 450 knots +/- TRUE airspeed, but 250ish knots INDICATED. Dropping the gear there would be LOUD, but within its operating limits. With millions of commercial airline flights per year, the answer to "has there ever" is surely "yes". Noteworthy enough to get its own internet article, doubtful. $\endgroup$ – Ralph J May 28 '18 at 4:27
  • $\begingroup$ @JanHudec It's certainly possible. Like I said, apply a large handful of salt. $\endgroup$ – a CVn May 28 '18 at 7:07
  • $\begingroup$ I have never heard of uncommanded gear extension/retraction. My guess is no it has never happened but a very thorough database search would be needed to confirm/disconfirm that. $\endgroup$ – kevin May 28 '18 at 7:33
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Typically it takes two points of failure for it to happen on a jetliner: the gear uplock to fail, and the door uplock to fail.

I found incidents where landing gear doors fell off jetliners, and only one incident where the gear uplock failed on an Airbus A320, but the door held it inside.

The crew had to slow down to a safe 'gear extended' speed.

A320 flight crew experiences a nose gear uplock failure climbing through FL200. Nose gear doors remain closed but aircraft is slowed to 220 KTS to comply with overspeed warning and ECAM logic (37000feet.com).

'L/G GEAR UPLOCK FAULT' is one of the abnormal procedures in the A320 flight crew operating manual. The first two items is to keep the landing gear down and a max speed of 280/.67.

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Only thing I can find is on the X-15 rocket plane. Expansion of the airframe caused the nose gear to come unhooked and deploy at Mach 4.2. The air friction tires and caused them to disintegrate on touchdown. The pilot was still able to make a safe landing.

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