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Standby instrument question?

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Nov 26, 2001
Ever notice that in the cockpits of some transport aircraft there is an incessant clicking noise when it is powered up. Does anybody know what it is from and what causes it?

I am pretty sure it has to do with the electrical standby AI. I think I was in a 757 sim or on the ground when someone pulled a breaker which I think was the standby AI breaker to stop the noise (obviously it was reset before flight).

Just wondering where it comes from and why it clicks. Thanks!!

MTOP hit the nail on the head, it is undoubtedly the vibrator beating the altimeter to keep it from sticking.

I was just about to ask why have a vibrator on the altimeter when hvyjetFo answered my question. :)

It all makes sense now. Thanks for the help!

Well it could be taken over by an evil being. I have seen a AI litrally spinning around as fast a top.

Funniest thing that I have ever seen on the ground. I could only imagine what I would have thought if I was flying and it did that.

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