Gear door actuators
 

Anyone familiar with "gland end" actuators for the main gear doors? I recently had a 'gear up landing' due to mechanical failure of the right main gear door actuator snap ring. It appears the snap ring gave way and the end of the actuator came out of the housing causing all the hydraulic fluid to pump out. I have heard that some later models have what is called a 'gland end' actuator where the end screws into the housing rather than a snap ring holding it in place. My Skymaster is a 1977 337G, normally aspirated, non-pressurized.

Gear Doors Removal
 

If you remove the Main doors with the mode, you will not ever have that problem. I did that 9 years ago and love that mode. It does not affect airspeed and you can put up gear as soon as you leave ground and have a cleaner climb out. It would have saved you thousands
of dollars on gear up landing. Dale

Hi Todd,

Sorry to hear of your misfortune but thanks for the info. I have a 1973G model. Same as yours, just a few years older. How many hours are on your airframe?

Thanks Ed

Was it the snap ring that failed or the lip it sits in, inside the actuator?

I can really appreciate the comments on the gear door mod, it would have saved thousands!

My airplane has about 800 hours total on it, engines and airframe. I don't know why the snap ring or groove it fits into failed, if there are actuators with ends that screw on, I would like to consider them. Anyone familiar with this?

If you're able, could you post another pic of the snap ring and the actuator open-end taken straight on and closer-up? Thanks.

Here's the additional photos.

It seems this is a rare situation. Any thoughts on why this failure would occur and how to prevent it other than using the gear door modification?

Had this been worked on recently?

New Cessna hydraulic hoses were installed in January. Since then, the aircraft had been flown approximately 60 hours.

I'm not sure I see anything wrong with the snap ring. It looks like the actuator housing let loose. Very hard to believe.

Those snap rings can be put in 2 ways, and only one way is correct. One edge is slightly beveled, the other is sharp. The proper way to put them in is with the sharp side out, it grabs the groove better. Do it backwards and you see the results. It is amazing how many mechanics don't know this. The newer actuators with screwed in end fittings were installed in mid '78 model year P-Skymasters ( P3370298 and on), I am not sure if or when they put them in other models. The good news is you can use the newer actuators in place of the older ones if you can find them, at least in the P models. My guess is that this is true for all 1973 and later models, but I only have documentation for the P Skymaster. You could check with Cessna, or Tom Carr at CPA. Hope this helps.

Another thought, probably a good idea to not reuse the snap rings here. New ones are cheap, and better economy it seems in this case. The snap ring that failed looks pretty worn to me. This is something that can be inspected at annual, I will add it to my list of stuff to put an extra critical eye on.....thanks for sharing, and I hope you get repaired and back in the air.

Thanks! That is exactly the information I was looking for on the screw-in end fitting. I really appreciate the help.:)

Hey Everyone....I wanted to mention that on the annual inspection that was just completed (10/1/09) on my 1973 337G model (no turbo/no pressure) I had my shop check the snap rings on the gear door actuators. They said they found one that was installed the wrong way. I have no idea how long it has been that way or how it got that way but as a direct result of this thread I had mine checked and they found the discrepancy. Thanks Todd!

Have those snap rings checked guys!

Ed

That's great Ed, I'm glad there has been some good come from my experience. The timing of your post is good because I am still undecided on whether I should replace the gear doors with the modification or put it back original with the "gland end" actuators that are available from Don Nieser. See part of an email communication below:

Todd I also looked at the Main Gear door actuators. The 1977 G parts catalog shows p/n 1580017-1 or -3 depending on aircraft serial number and the early model 337's and 0-2 aircraft used p/n 1280513-3 or alternate 1298110-3. I further checked and they all use the same door p/n, the same door hinge p/n and the same actuator mount p/n and the fuselage is no different at the rear firewall. Therefore my conclusion is that the early model 337 actuators and 0-2 actuator will work on your aircraft. The problem is getting approval. Attached are photos of the end of actuators like yours with the snap ring and a photo of an early model 337 actuator that does not have the snap ring. I have 3 of the p/n 1580017-1 and one p/n 1580017-3 actuators as removed for $950 each and a number of the p/n
1280513-3 as removed actuators for $750 each. Let me know and I can ship these parts to you right away.

I would still be looking at getting approval, but I think it would be worth the 'peace of mind', knowing the end of the actuator is more unlikely to fail than with the snap ring.

I have also attached the pictures.

Any advise and/or opinions are welcome. Original gear doors or replace with gear door mod?

I know this topic has been thoroughly discussed on this forum in previous posts, and I have read them. Any additional or fresh thoughts?