Thursday, March 29, 2007

Gremlins

I wish I had written about this when I first got the notion. Some of the details were flaky to begin with and now they are fuzzy.

We have and old C90 King Air in the shop at the moment. It was supposed to be gone already but the Gremlins attacked. Actually, some of them have been lurking around for a while.

Last week I heard they (I am not directly involved now) were having trouble with elevator trim. Works on the ground but it hangs up in flight.

I had been involved early on and knew that the trim cables, tensions etc were good from the aft pressure bulkhead to the end of the line. Forward of the bulkhead, I didn't see or do much with it.

This week I wondered if the grease in the actuators had turned to soup. (It's scary to see how much water and watery grease with come out of a prop cuff when you purge it.) Maybe that was freezing in flight.

The guys have been from one end to the other. All of the routing is right. Pulleys are free and no flat spots. they disconnected things and worked the system by hand in attempts to narrow it down.

They really haven't found anything of substance. They said the trim wheel is a little stiffer as you roll it through Zero my it's only noticable if you turn it really slow.

As if that wasn't odd, the real weird stuff begins at 7000 feet.

As you reach 7000 ft-
Intermittant static in the headset
L/H fuel quantity needle starts to swing
Prop Sync fails
R/H fuel Qty will sometimes fail
And, some other unrelated system fails (I don't recall which)

This bug has been a problem for a while apparenty.

The owner has had the fuel quantity system investigated from wing tip to gages to wing tip with no results. Other troubleshooting has been done as well. (All of this work performed elsewhere I think.)

They have done test flights. Shutting down one generator then the other. Pulled circuit breakers one at a time. (Every circuit breaker in the panel.)

Oh, it doesn't show up if you pressurize the plane in the hangar either, of course.

Hey, I guess that's one reason to look forward to going back to work tomorrow!

I realize that I lost 95% of you at, "old C90..." but wanted to throw this head scratcher out there for the other 5%.

1 comment:

Bob Barbanes said...

Temperature related? Intermittent problems with usually-unconnected accessories are a bitch.