My partner George had a MLG retract problem Friday the 6th on a business trip to California. Left gear would not retract. He landed at nearby Marana Regional and tried to determine the cause. He serviced the hydraulic reservoir, but it was only marginally low. Unfortunately there was no local talent about with Sierra experience, so he stiff legged it back to 57AZ (La Cholla Airpark). I went to the airplane the next day, but was unable to find jacks on the field. There are plenty available, but nobody was around on that Saturday morning. I busied myself with some other minor stuff for an hour or so, then closed up shop and went home.

Yesterday I went back to see if I could find some jacks. I decided to remove the actuator panel and saw that one end was no longer connected. You can see by the poor quality photo how the rod end failed. Looking with magnification I found the source of the initial failure was due to corrosion between the grease fitting and the rod end. A very small crack developed before failure. The second break was a complete catastrophic failure, no doubt from overload. It was interesting to note, I haven't as yet found one ball bearing in the actuator compartment. The inner bearing is still in the trunnion fitting as the attach bolt can only be removed with the gear up. I did find jacks, but the guy had a student preparing for her Private Check Ride and didn't have time to head back to his shop (home). It was getting close to lunch, so I left for home as I didn't want to leave the airplane on jacks for a week or so as I don't have any rod ends laying around.

The rod end appears to be a MS 21151series or similar. I think this might not be the best applicaton for a double row bearing rod end. I think a spherical bearing type rod end would be better suited for this application. As the actuator is in an enclosed area, a sealed bearing would probably be ok.

My concern is what caused the failure? The crack at the grease fitting hole doesn't appear to be of sufficent size to account for the failure. It extends accross the hole about 1/16" on each side an only a 1/16" deep. The second failure probably occured when the actuator tried to pull the broken rod end between the still attached inner bearing and the trunnion body. I suspect we will find some binding in the trunnion bearings once we have the airplane up on jacks and can check the gear. It is my intention to check EVERYTHING with the gear. If we don't find the smoking gun, we will dissemble the gear until we do. Also, I'd like to do a search for the bearings.

I have the AMM/Shop Manual but not an IPC. Can someone identify the part number of the MLG extend/retract actuator rod end?


Marty Vanover
Phoenix, Az.

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