Gear Failure

[Roger]

Yesterday after having my plane sit for a month without flying (due to the terrible weather in the North East) I finally got a break. If has been it the hanger (non-heated) since it came through its annual a month ago, which included 3 gears swings.

I preheated the hanger for 2 hours with all doors open, plus preheated the engines with the block heater, and departed in 10f temps.

After takeoff and "gear up" the gear doors would not close, and after a minute or so it popped the gear circuit breaker. I reset the breaker and recycled the gear down. No prob, gear down, doors closed.

Cycled them up, no problem, and doors closed, but the in transit light flickered for a couple of minutes, then went out.

Flew to my dest (an hour) and cycled the gear. Nothing ! No popped breaker, not noises, no gear no doors. Popped the breaker manually and reset, nothing. Master off, master on, cycle the handle. Nothing.

Put the gear handle in the down position, reached down and extended the hand pump, pulled it up 1/4" and it snapped out of my hand back down, and gear immediately extended, and doors closed.

I forgot to mention the part of me overflying the airport trying to decide if it would be better to belly in on the ice covered runway, or the hard paced snow between the runway and the taxiway.

So the question is, what do the doors not closing on the up cycle have to do with the gear not coming down until I gave a slight uplift to the manual pump handle?

Any thoughts would be appreciated. 337H - 1980

tks/Roger

[Skymaster337B]

I believe in order for the gear doors to close after the gear is up, that not only do all gear have to be in the uplocked position; but then the shuttle valve drops the hyd press down to close the doors. So if the doors didn't close and the gear really locked in the up position, then I'd say you might have shuttle valve issues.
In which case the pump will run at the higher pressure for as long as it takes to overheat the electrical pump...causing a breaker to pop.

So when you pulled the handle, it may have hydraulically jarred a shuttle valve so that it would move normally again.

[Dave Underwood]

I don't have my POH with me, but I am I correct in thinking you also have to turn the alternators off as well as the master so the system would reset itself fully?

My experience has been that the micro-switches can cause lots of issues and the flickering in transit light might be a clue. You might want to check the rigging of all the switches.

In a similar although not exact event, we found one of micro-switches was intermitant. The gear came up, in transit light stayed on and pump continued to run. I put gear down ok and flew home like that.

On another occasion we figure it was air loads preventing the door close circuit completing and that valve changing to close the doors.

I now get the maintenance folks to pretty thoroughly recheck the rigging including the position of the down locks while the gear is in transit down to try and minimize the potential problems.

Blue skies.
Dave

[Pete Somers]

Yes Dave, that is exactly what i would check, the trouble with those microswitches on the main gear is that due to the different load and airflow they must be adjusted to positively make contact and a little bit more.
As Dave says, get your mech to check the switches before you go for the shuttle valve in the power pack.

Pete

[Kim Geyer]

I would check the solonoids. they get small amounts of hyd. fluid inside of them and in cold weather they get real sticky.
Kim

[Skymaster337B]

This is why I carry insurance on my plane. Because you never know when the landing gear will take a mind of it's own. And I totally agree...check micro switches first!

[Jim Rainer]

Don't have a good answer, but I believe the reason the extended gear handle jumped out of your hand is that you did not pull the circuit breaker on the gear pump. My POH says to extend the gear manually 1) pull the gear motor CB; 2) put the switch in the "down" position and 3) then pump gear down - takes a lot of pumps.

I'm glad to know the gear handle jumps back to the down position when you try to pump it without pulling the CB. I've always wondered if I forgot to pull the CB would the handle jump up and break my arm!

I've had a similar problem in that the gear would not retract and the cure was to pull the CB, put the handle in the "down" position then crank the gear down - only a few pulls since it's already down, then push in the CB and voila! the gear would retract when I put the switch in the "up" position and pushed in the CB. Cured itself after a little while.

[Kim Geyer]

I've seen the rubber buss bar cover in the nose wheel well come loose, blow in the back of the well and keep the nose gear from fully retracting. doors won't close, motor won't shut off' breaker pops.
I've also had a main gear uplock hook get out of alignment and about 1 in 5 retracts the hook would not fully engage the leg.
Hope this helps
Kim

[Roger]

Thanks for all of the advise. We are into the project now, after letting it warm up in a heated hanger. I will post the repair if we find it.