Attitude Indicator MTBF

[skidoo]

So, I get the plane out of annual and the backup AI tumbles at start up. It seemed fine the next day. So, I start wondering what the MTBF is for a typical air operated gyro? I'm also wondering if this is common and may be fine for many hours more, or does it mean the gyro has failed or is soon to fail? I'm not sure that it is really stable now, but I will check it closely on the next flight.

 

[peter-h]

They last from a few hundred to a few thousand hours.

Not sure what that makes the MTBF

My KI-256 lasted ~ 800hrs and the replacement lasted ~ 200hrs. I hear from the overhauler of the last one (I bought a new OH unit from Castleberry) that they ordered new bearings from Honeywell but they were defective, and they are still waiting for a new (good) set, ~ 6 months later.