AI failure modes

GeorgeC

GeorgeC

Administrator
Management Council Member
Joined
Dec 5, 2010
Messages
5,175
Display Name
Display name:
GeorgeC
What would cause this (not my video) on a 172M/O320?

http://www.youtube.com/watch?v=huFjpyDTP9w

I got that today. Vacuum gauge was on the peg until I did the runup to 1700 rpm. The situation did not resolve so I scrubbed the flight and squawked the inop AI. The plane had been flown earlier in the day and it was already relatively warm.
 
GeorgeC said:
What would cause this (not my video) on a 172M/O320?

http://www.youtube.com/watch?v=huFjpyDTP9w

I got that today. Vacuum gauge was on the peg until I did the runup to 1700 rpm. The situation did not resolve so I scrubbed the flight and squawked the inop AI. The plane had been flown earlier in the day and it was already relatively warm.
Click to expand...
Which peg? This looks like low pressure across the gyro. It can also happen with a perfectly good gyro and air pressure if the plane is shut down briefly letting the gyro spin down part way without stopping completely.
 
The "0" peg.
 
A couple of busted vanes in the vaccum pump would do that...Suck/nosuck pulses and no real vaccum until higher RPM.

Just a WAG and worth every penny you paid for it...


Chris
A&P Skool student:redface:
 
Ok, I'll bite... Bad flying? ;)

It could be a number of things; vacuum leak, poor vacuum, gyro uncaged, etc.
 
Last edited:
Unless that is your overly aggressive attempt to track a localizer, I suspect one of two things:

1. Very low but not zero vacuum pressure which causes the gyro to start but not enough to erect properly.

2. Something internally wrong with the erection vanes in the gyro.

While gyros generally settle down within a a minute of having sufficient vacuum applied to them, they really aren't entirely stable for several minutes. There was a crash a few years back where a bizjet did a quick start and launch into IMC before his gyros were table.
 
It turned out that there was a problem with the vacuum system, not the AI itself.
 
You must log in or register to reply here.
Back
Top