Main gear door issue

billsheila · #1 07-12-12, 09:29 PM

On my '65. The issue is every now and again I land and find the pilots side main door wide open like a very effective air brake. If I turn the master back on and hand pump, no problem it closes right up. It doesn't happen every time. Anybody got any ideas?

My understanding of the sequence is that after the light is triggered (gear up or gear down) then the solenoid is powered, moves something on the power pack to actuate the door hydraulics. Doors close, pressure builds until enough is achieved to move handle. My handle is returning and I am getting light...all normal. But then I land to find the one big door open?

Thanks in advance for any ideas.

Bill

hharney · #2 07-13-12, 12:20 AM

Does the door close and then re-open in flight or is it just not closing in flight? I assume it stays closed when the gear is retracted?

billsheila · #3 07-13-12, 07:25 AM

Herb I cant tell or rather don't know at this time. I only have a mirror on one side and cannot see the rear big doors with it in any event. With pressure building and the handle returning, my guess would be that it is initially closing. But if the pressure that holds it up is then relaxing somehow, which I guess could be happening, I wonder why the other door(s) would not also fall open? I presume that there is only one main hydraulic line that operates the doors (out of the powerpack) that at some point branches off for the various door actuators.

This airplane is getting frustrating this annual...one issue cropping up after the next! I better get to the bottom of things soon...the fly in will soon be upon us! Thanks. Bill

hharney · #4 07-13-12, 02:42 PM

Bill
You need to see what is happening or swing the gear on jacks where you can determine the scenario. I was thinking that there is a separate actuator for each main door...........I will need to look at the print but that was part of the advantage of removing the main doors to eliminate two actuators.

hew · #5 07-14-12, 05:53 AM

The rear doors operate off a tee on the rear bulkhead so there is no reason the pressure would not be the same on both sides, unless there is air in the door close line (top tee) going to the outside of the actuator but normally it should self purge.

billsheila · #6 07-14-12, 08:30 AM

I was wondering where the split in the hydaulics was, so thanks for that inofrmation. I suppose the line or actuator or the tee you mention could have a clog or obstruction, so maybe that is worth checking. Related question...what holds the doors closed? Is it just the built up pressure from the handle movement that holds? I ask because I wonder if I am losing pressure somehow, but of course that would not explain why all the doors are not just falling open. Again, any thoughts or theories here are appreciated. Thanks.

Bill

hharney · #7 07-14-12, 08:59 PM

Bill

The main gear door actuators are held closed with hydraulic pressure. See attached diagram. If only one door coming down it lends that the system is losing pressure. It could be the door actuator on the subject door. There are no uplocks on the doors as I was reading the print incorrectly.

The main gear actuators are tee connected in with the strut door actuators. Of course there is micro switches that have to be satisfied. Sounds like an actuator on the main door is leaking down.

Skymaster337B · #8 07-15-12, 12:39 AM

The way I see the diagram is, the main gear door pressure is trapped between the two actuators. This effectively hydraulic-locks the doors in place. So, my guess is there's an internal leak in one of your gear door actuators. Very easy to overhaul...mostly new o-rings, and of course a proprietary Cessna teflon "back-up seal" that will cost almost as much as socialized health care. The other possibility is the door solenoid in the power pack.

Skymaster337B · #9 07-15-12, 01:05 AM

Does your gear door also creep open while the aircraft is parked and not flown for a few days? If so, there is a thermal relief valve in the hydraulic power pack that helps keep the doors closed during thermal expansion. However, this thermal relief valve was not installed on earlier model 337's, unless the power pack was replaced with a new one. Therefore, during thermal expansion the main gear door will open.