Landing gear doors won't close
 

It's really pretty simple but thought I would post an issue we resolved for fun and to keep us sharp with these aging birds.

I just finished flying 20 or so hours in Nova Scotia (should have been there with us, it was amazing flying adventure) and got home last Thursday. Plane sat in the hanger Friday and jumped in Saturday for the annual Newman's Breakfast Fly in (4N0) at Larry's airport. When I departed Riverview runway 14 (08C) I turned right toward Kzoo and reached to retract the landing gear. I noticed that the amber light was flashing and I could virtually feel the gear doors opening and closing at a fast rate. I pulled the gear handle manually to neutral to stop the hydraulic system operation. I looked out to the mirror on the wing and the doors were open. Uhmmmm. I extended the gear, that operation was normal and then retracted the gear up again. It went up normally. Ok, all good...................not!

FYI, "1968" "C" model, so the hydraulic pump is on the front engine. Later models, 1973 and on, had the electric pump unit.

Do tell! The doors were repeatedly opening and closing while the gear was retracted?

Yes, very quickly and violently. Once I manually selected neutral on the gear handle (remember this is the older gear system with the engine driven pump) it stopped but the doors remained open.

Was it a failure in the pump itself that caused it to oscillate between pressure & no pressure on each revolution?

So off to the shop and up on jacks. After taking the time to raise the airframe I opened the doors and started a visual inspection of the up lock switches. I started with the right main as I exited the cabin from extending the doors only. As I looked at the micro switch it looked ok but I touched the wires to see how secure they were and one of the wires came right off in my hand. BINGO!!!!! Here's the problem, why did I take the time to put the plane on jacks? I could have identified that without jacking the plane. While Craig replaced the both connectors on the switch I prepared to lower the plane back to the floor. We removed the jacks and pulled the plane out so that I can be on my way back home and prepare for the trip to NYC the next day in the early AM. As I departed I selected the landing gear up and the gear doors still did not close. WHAT!!!!! You have got to be kidding me. I circled around and started the downwind to land while trying the gear retract several times. No good, back to the shop and it's already 6 PM. Now what?

With these symptoms it's got to be an up-lock switch. The system protects the door from colliding with the gear until the up-lock switch's are satisfied........

Post discrepancy
 

Herb - in your first post, you indicate at the end of the post, after cycling the gear, it came up normally. Does that mean that the gear doors closed on that last cycle, or in ALL cases, the doors never closed? Just trying to understand if this was intermittent, or a hard failure. Do the doors close when the gear is down and locked?
Jeff

Herb
Did y'all check the door switch that's mounted on the power pack? Sounds like that switch might be a little out for rig

Jeff
Yes the doors did close some of the time. It was intermittent. They always closed with the gear extended.

Kim

Are you thinking the over pressure switch? Mines the older system with the pump on the engine.....

There is a switch mounted on the bottom aft of the power pack. if you follow the linkage from the landing gear handle to the power pack is mounted on the outboard side of the power pack where the shaft goes through. it operates the doors to closed when the handle is in the neutral position. at least that where it is on our 337E
Kim

No Kim that wasn't the problem in this issue. I looked over the schematics and I think you are referring to the DOOR SOLENOID. I have never had any issues with this valve or switch.

When I returned to the shop after finding the wire loose on the up lock switch, main gear, right side, we were baffled that the new connectors didn't fix the problem. We decided not to put it back on jacks but to ohm out the up lock switches on the mains and the nose. While testing the nose we did not have continuity on the nose gear switch. I could not believe this. Finding a loose wire on the right main and now the nose switch wasn't working????? Ok off with the nose gear up lock switch and sure enough there was a broken wire. Now I am questioning which wire was the culprit.

After repairing the nose gear switch I took her to the air again and NO WAY!!!! the doors still did not close, how could this be happening. I landed and taxied back to the shop with pure discouragement. We put the plane back on the jacks and retracted the gear and started testing the switches again. Come to find out the new connectors that were installed were defective. One of them was not making contact. It was so crazy. We changed both the connectors with new connectors from another batch and off to the air again. It worked, the doors closed. These wires and components on these 50 + year old airplanes are starting to fail and we need to be ready to start getting proactive with inspecting closer. I was never in a gear up landing issue but it could happen the other way.

Gear Swings
 

Herb,
I am pleased to hear you found the culprit. I don't mean to call you out, but maybe as a reminder to all of us, that it is best practice to perform a gear swing after any gear maintenance that could affect the operation, indication or function of the gear. I am not sure what the Cessna manuals say - but I follow a simple rule; always perform landing gear tests (gear swing) in the hangar after such maintenance, especially when at a maintenance base. It not only ensures you fixed the problem, but in most cases can also reduce any in-flight turn backs or cancelled trips. I know, some problems can't be detected on the ground - but if we use Herb's case as an example - the problem most likely would have shown itself if they had tested the landing gear after initially fixing the first main gear switch wire.

Trust that you have found the problem, but don't forget to verify. This is true for all systems.

Side story - the other day, a friend of ours called me thinking she heard someone in her house in the night (she distinctly heard some one striking some piano keys). She was pretty shaken up. I went home with her and checked the entire house, inside and out. No signs of entry, everything looked secure, so we chalked it up to something strange with the electronic system on the player piano, and unplugged it. Besides, she had the house alarm armed the whole time. I went to leave from the front door (we had entered through the garage) and as I went to close the door, there was her house key still in the lock on the outside! Wow - she forgot it when she walked the dog the night before. Well, maybe this is just a freaky coincidence...the alarm was set, right? Right. "Trust, but verify". Let's test the alarm before I go - and guess what - all entry points in the house would set the alarm off...except the front door.

Trust, but verify.

Jeff

In order to test the gear on jacks I would have had to remove the hydraulic pump. Wasn't going to do that for this exercise unless the problem could not be found. I was departing for NYC the next morning so removing the pump was not in the agenda. I did use the hand pump for the last chase in this exercise but normally do not like to use the hand E pump for retraction. The gear pump removal and remount can take up to 4 hours. Just didn't have the time to do this for this type issue.