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Joe Stack writes:

>    As for the attitude indicator failure in IMC, I too have been there, 
> done that.  It
>    was a dramatic event, the gyro tumbled violently (and, as near as I can 
> tell I
>    survived).  For the record, the problem with vacuum driven instruments 
> is not the
>    gyros; rather it is the vacuum pumps.  I have also seen the insidious 
> method of
>    pump failure; it happens so slowly that a busy or inattentive IFR pilot 
> could easily fly
>    into an unrecoverable unusual attitude by following it. (John Deacon 
> published an
>    excellent article on this very subject a few years back on AVWEB).

My AI failure was the insidious type you mentioned.  The vaccuum pump spline 
broke and the AI slowly fell over as the gyro slowly ran down.  I caught it 
within a minute or so (I believe) when cross-check was telling me something was 

FWIW, I had this in mind when I spoke with the folks at Sierra, who say they 
have the ability to run the AI for 45 minutes on backup battery.  Again, we have 
to assume that complete electrical failure or dare I say electrical fire prevent 
use of the electrical system at all.  If I go EFIS I will have vaccuum pump as 

David Karas