Gear Doors Don't Retract on 66 337A

Gear Doors Not Closing on a 1966 337A front engine gear pump only. Here's the scenario.

Some of the details may be irrelevant, but I'm going to give the long boring version in case someone sees a relevant pattern.

Thursday, start up, call clearance, and my primary com radio starts to get some static, blinks a couple of times and then dies. I turn it off, back on, and it works fine for another 5-10 minutes. Exact same thing happens again, but this time, radio is dead.

I call a shop, and have them get me a loaner, which I swap out on Friday. Radio works fine!

On my way home (about 1 hour into a 4 hour flight) I scan everything and notice that the circuit breaker for the rear "generator" had popped (this had to happen in flight because I checked it during run up and it had not popped). I looked at everything else, and the front alternator had obviously pulled its weight nicely, everything electrical read normal. Reset it, and it never popped again.

About another hour into the flight, I noticed that my yellow gear up indicator blinked off. I didn't think too much about it because I looked outside and doors and gear were still up, so I assumed a faulty bulb (and no, I didn't switch it out with another bulb from my marker beacons or the green light at that time . . . but it did cross my mind) and kept flying.

Got home, on downwind, put the gear lever to down position, and got a visual on the gear, but the green light won't come on nor will the gear handle go to the neutral position, and I can see in my mirrors that the gear doors are stuck open. Tower wanted me to do a fly by so they could take a closer look. I did, they confirmed that the gear looked fully extended, but the doors were wide open. I flew a few miles out, and tried hand pumping the doors closed. I did this with the handle in the full down position, and then tried it with the handle in the neutral position. Then I turned my master off (not the alternators however) and tried it again, no luck!

I tried to recycle the gear several times, but everytime I did, even in the up position, the gear would fully retract but the gear doors would not shut. Tried pumping again with the handle in both positions, and it didn't work.

Finally, I went back, and landed without incident. And . . . by the way, I was one of those folks that once I knew I had the 5100' runway made with relatively calm winds, I killed my front engine and had the prop stop horizontal to make sure that if the nose gear collapsed, I wasn't going to have a prop strike on the front engine (it ain't tough to do on these planes - but I know I'll get criticism anyway). Everything was fine. Taxied over to the hangar on the rear engine, shut everything down and turn everything off, then turned the master switch back on, and manually pumped up the gear doors easily, and the green light came on instantly after the doors were closed. And yes, I tested the yellow light, and it also worked.

The thing that I didn't do, which I wish I had done in hindsight, was to kick some hard rudder back and forth and then do some porpoising to see if I could have "unstuck" or moved whatever wire, switch or whatever it was to a happier position.

Any thoughts on what gremlin may be lurking in my landing gear doors? To me, it sounds electrical, thus the whole diatribe on the electrical events of the day.

Thanks,

Keven
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SophiaHot

[Ernie Martin]

Keven:

Don't have much advice but wanted to make some comments.

First, there's almost an undercurrent in your write-up as if you could have done more in flight. In my view, you did everything by the book. Your most important task is to fly the plane, not get distracted. I'm surprised at how much you did do, from taking note of what was happening to active diagnostics.

Second, although I'm a firm believer that when two things go awry they are likely to be related, this doesn't sound like it. From what I remember of my 1969 337D (my current 337G has the electric powerpack), the pump puts out the muscle through the hydraulic lines and actuators, and the electrical system is there only to sequence the process via the switches (e.g., gear doesn't start coming down until switches show doors are open). So if you had adequate voltage to run electronics in the pattern, you ought to have adequate voltage to sense the position of a switch (in short, this is not a load per se).

What's harder to figure is why the manual pump wouldn't close the doors in flight after you put the gear down, but did it on the ground. Here's a question on that: did you have the same electric loads on when you pump them up on the ground? Despite my feeling in the paragraph above that it doesn't sound electrical, it would be nice to know if all loads were the same.

Good luck and please post your findings.

Ernie

Ernie:

Loads were not the same on the ground. The only electrical thing I had on while on the ground was the master switch. Everything else was off.

Jim Stack has sent me some info and diagrams concerning the probable gremlin. I'll report back after I check that/those out. I'm too ignorant to try to explain it here without studying the diagrams he sent to me first.

Meanwhile, if anyone else has any suggestions, I'm all ears, uh, err, eyes.

Thanks,

Keven
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Vaporizerinfo.Com

[skymstr02]

Check the electrical solenoid valve on the back of the powerpack. The plunger in it sometimes gets gummed up by hydraulic fluid residue. It also gets hot and any fluid residue can get gummy and impede the plunger (controls the hydraulic fluid flow to the door actuators).

I've seen this many times on pre '73 337 series airplanes.

Dave

[rick bell]

i have had problem with gear and avonics togeather, it is usally associated with low voltage. weak batteries will cause the gear not to function properly and make the radios work sporadically.
usally it is a combination of things, very weak battery, and after starting it is really drained, so radios start going wacko with transit voltages. the gear take most of the amperage however the weak or bad battery will consumue most of the voltage before the gear hyd. packs gets it's. as the gear cycles torward the end of the cycle that is where the highest amperage is. if you change celnoids, change all four, they are ages and proned to stick (cheap less tha 30 ea). i have many time had the a/c jacked and the gear operate fine; however it is usally connected to an outside power source as not to drain the battery, so if you jack it try it without an outside power source (you can always recharge the battery and your condition will be more realistic to flight conditions, especially if you put pressure on the gear as it retracts and extends). also the squat switch have a tendency to act unpredicatable before they fail. so soometime it will give signal that the a/c is still on the ground during it's cycling (which will confuse you with the different indications, doors open but the gear doesn't retract or extend or the opposite) you can check the squat by going in the nose gear well and follow the wire to the terminal strip, jumper across the leads and cycle the gear, if it works the squat is bad and cessena will send you a new one for 180 for a 15 switch.

[Mark Hislop]

Keven

I have had exactly the same problem, although my aircraft is a '73 P337. The gear would cycle down, but the doors would not close, and the gear motor would keep running. The gear would go back up, and the doors would close. Put the gear back down, and once again the doors stayed open, and the pump kept running. I pulled the LG circuit breaker and landed. Once on the ground, put the plane on jacks, and everything worked perfectly. Back in the air, the problem repeated itself...gear would come down and lock, but the doors would not close.

What caused the problem was the limit switch that indicates the gear is down and locked. Even though the gear operated properly, and was down and locked, the limit switch did not indicate so. The limit switch (actually three limit switches, one on each gear) must close, so that the valves can then direct hydraulic pressure to the door actuators and close the doors.

In my case, an adjusting shim had fallen out, and the limit switch on the right main gear was not making contact when there were air loads on the gear. Without the air load present, when the plane was on jacks, the limit switch made contact. Other problems with the switches could include intermittant contact at the terminals, dirt in the switches, or broken wires. There is a limit switch on each gear. I'll bet this is where your problem is.

By the way, shutting down the front engine when you have suspected gear problems is a procedure listed in the POH in my aircraft. I did the same thing.

Mark

[Dale Campbell]

Keven,
Mark is on the right track. I had the same thing happen to me last year. I was two weeks past my last annual when the gear went down and the doors stayed open on my 337H. I did basicly the same thing. When doors did not close after gear went down. I pulled LG breaker and tryied the hand pump. I tried putting gear back up and down 3 times with same thing happening. For that the mechanic gave me hell, when I told him later. He said if the gear looks down and you tried the hand pump , leave it down. His theory is. If you have a broken hydraulic line that may be your last chance to get it down. I called the mechanic on the ground to check my gear on a low fly by to verify the gear looked locked down. He said it looked fine. So I landed. Just before the gear touched, I pushed the breaker back in so I had pressure on the system. When the gear touched the runway the doors closed.
We put it up on jacks and cycled it 10 times, the gear worked fine.
Two days later the same thing happened. This time I was back home where my regular A&P put it up on jacks. We found it this time. On the main gear leg there is a "U" shapped stricker plate epoxied to gear leg, that closes the limit switch. It was loose on gear. We removed, cleaned and re-epoxied it to gear leg. That ended that problem.

[Mark Hislop]

Dale:

I did not hesitate to try and recycle my gear because the gear pump was still running "hard" and I felt it was making pressure. Also, there was a great deal of resistance on the hand pump, so much so that I was afraid I would bend the handle. If there is a hole in the line, there will be no pressure buildup. Otherwise, I would agree with him wholeheartedly.

Mark

[Richard]

We have the older mechanical unit as opposed to the electrical-hydraulic unit. I've just overhauled my entire landing gear system and feel I'm getting a pretty good understanding of it. I think it was said earlier, but the power pack uses and electical actuated plunger to switch from gear to gear doors. It is easy to take off, it should be on "hand tight". If this unit is good, then the 28+ from the switches are not getting to the unit and would suspect one of your microswitches. My two cents.

I was told by a hydraulic shop, that these units should be overhauled every 1500 hours. Mine had 3000 hours on it. Still looked good, but as with ALL hydraulic assemblies they collect ALOT of very fine metal from the pump gears after that length of time. Might be a good idea just to open the top and check it out. You will have to drain the fluid in the resevoir first if you do.

Richard

Jim:

As a follow up, here's the status.

IA took it in and checked all of the switches, cleaned them, and put everything back. Of course . . . it worked on the mule. And of course, the next time I flew it . . . it didn't.

So, it was off to chase electrical gremlins. And he chased, and he chased, and he chased it, right to the "power pack" as everyone calls it. On my bird, it is located just above the left side of the pilot's feet. This is a monstrous piece of equipment. The electrical tests showed that one of the solenoids on the pack was bad.

Cessna quoted to my IA 160 days lead time, $6,000. No, that's NOT a type for a 2" x 1" cylinder solenoid. Ahh, but the financial news got better. IA found a used core that had to be overhauled. . . punchline, for just that little solenoid, $1,800, not including overhaul. And people think lawyers don't have a conscience!

Fortunately, I just purchased another 337A as a parts plane, and its solenoid worked fine. It was, shall we say, a challenge, to remove it, but, we got it out without damage. Crisis and 2d mortgage averted!

I haven't flown it since then. I'm going to Ohio Friday afternoon, so I'll find out sometime Thursday afternoon or Friday a.m. before I leave if it really works.

The ONLY good news from this is that I now know that my entire system has been revamped and cleaned, including hydraulics, contacts, switches, fluid, etc. so hopefully, the gear gremlins will leave me alone for a long time.

That's the latest and greatest.

Keven
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LovelyWendie

[rick bell]

all the synolids (?) are basically automotice, i replace all four of mine at around 30 bucks each . sometime as wiring gets old it get brittle, so what you have is it works then it doesn't and th same with squat and down and locked or up and locked. i have had my a/c up on jacks many time and it always works (even with putting a load on the cycle) the lasttime it was a squat that was gong bad and would work then not. one time few 200 miles with the gear 1/2 retracted (the bose wheel makes a great front rudder and really tires out the foot). i shorted out the squat switch wires and the gear worked perfect, replace the sw and all is fine. the other time it was a broken wire at the up lock switch which indicated the gear was not down and locked, this may not help at it is a 73p; however it is realative and it usally comes down to broken wires or switches/