Gear doors won't close on ground...

Pete Somers · #1 09-23-08, 09:16 AM

Looking at the diagram this looks like you have a sticking door solenoid valve or a wire broken on the solenoid itself, need need to check if there is 24 volts on the solenoid, if so the problem is the power pack, if not check the wire from the gear handle to the solenoid.

Pete

skymstr02 · #2 09-23-08, 09:49 AM

The same thing happened on my O-2A, and it turned out to be the microswitch on the powerpack that controls the solenoid. The switch mimics the solenoid troubleshooting, and this particular switch is not called out in the airframe wiring manuals, but is in the illustrated parts listing.

atsiii · #3 09-23-08, 10:04 AM

Thanks Skymstr02! Back in 1999, that same micro-switch had to be replaced on the '69 I was flying then, so I was suspect of it. It's a 3-wire switch but I can't find a diagram to know what each wire should be. I still have the '69 as a parts plane, so maybe I should just change it...

skymstr02 · #4 09-23-08, 12:16 PM

I just bought the switch from Yingling for $30, they had it in stock. There are actually four terminals to this switch, and the actuator button is in the center, which makes this unique. Two of the terminals are wired together so this makes this a single pole, double throw microswitch.

Take the white plastic drain tray off from under the powerpack, and you will see it towards your instrument panel. There are three wires going to a terminal board on the bottom of the powerpack, so you can take the switch and wires off as a unit.

stackj · #5 09-23-08, 04:31 PM

I am attaching a scanned diagram given to me by a friend. This looks like part of a text from some mechanics school who teaches Skymaster systems, but I can't find any reference on this package to either ask permission or credit them. Anyway, I'm chancing making this available because it is a much simplified diagram of the gear door permissive systems... Here it is. When you zoom in on the picture the text is more readable.

The Key to remember. If power is off at the Landing Gear Door Solenoid and Hydraulic pressure is applied, the doors will open.
If power is on at the same solenoid and hydraulic pressure is applied, the doors will close.

atsiii · #6 09-23-08, 05:03 PM

Thank you, Jim & Skymstr02!

atsiii · #7 09-23-08, 09:52 AM

Thanks, Pete! Yes, the gear down light is on. The gear did swing fine during the annual, multiple times. The a/c was then towed back to my hangar, sat for a couple of weeks until I had time to put it back together, and then, after replacing the inspection covers, the carpet and seats and getting ready for the post annual shake down flight, I pumped the doors open for inspection and they would not close.

I'll pass on your suggestions to my IA. Question: Is the door solenoid valve attached to and located on the back of the hydraulic pack above the pilot knees?

If so, I can't see how to get in there and check voltages or to look for a broken wire. If stuck, I read that I should hold a steel ruler next to the solenoid to check for a magnetic field, but I could not see how to get in there and do that, either. There are three wires to a micro-switch on the front of the pack, but I can't find the wiring diagram in my service manual to see what these wires should be, nor track them to the back of the pack.

Since the gear was swung during annual, I thought maybe I had done something while putting the carpet back in. But if the door solenoid is up by the hydraulic pack, I didn't replace anything in that area. FYI: after the a/c sits overnight, the emergency hand pump pressure drains off, but then with the master on or off, and the gear handle down or down-neutral, it only takes a partial pump or two for the handle to be firm with pressure again.

Thanks again! Let me know if you think of anything else to check. Question: do you think if the valve is just stuck, that I should fire up an engine and try cycling the the gear handle between down and down neutral?

Allen