Landing Gear Actuator & Component Malfunction

[TCW3]

For those of us flying vintage models, we expect a few parts to wear out here and there. I wanted to share a recent experience that resulted in an in-flight emergency as it could be simple, preventative maintenance for some. 

About a month ago, I went on the first flight following reinstallation of the gear actuator in my 1970 M20F. To comply with AD 75-23-04 I had to actuator removed, shipped to a Mooney Service Center, then reinstalled. All things checked out for the most part. The service center replaced a handful of parts that were worn, but nothing major - thank goodness the actuator passed and appears to have a lot of life ahead of it. 

To keep the story short, the gear failed to deploy on the return flight the first time I went up. I aborted the landing, went up for some altitude and spent some time troubleshooting before going through the emergency gear extension procedure. No gear down light, nor alignment on the visual window between the seats. Checked the circuit breakers (CB) and found the gear actuator CB to be tripped. This was odd because I did two touch-n-go landings before leaving the area with no issue.  And as far as the panel, the lights were working properly, which was very confusing when trying to troubleshoot. (Actuator test proved the bulbs weren't blown.) 

The meat of what I wanted to share for other owners: 

For the electric gear extension and retraction to function properly, there are two micro switches that work with the actuator. In the belly, attached to a rod, these two switches are in fixed positions. There is a plate attached to another rod that moves forward and back depending on whether the gear actuator is raising or lowering the gear. That plate, once at the right position, presses the button on the switch. For raising the gear, the switch turns on the Gear Up light and signals the gear actuator to stop. Same process for the other, but for the Gear Down light. Signaling to the gear actuator to stop is the important piece.

If either of these switches malfunction, the gear actuator won't know to turn off and instead trip the CB for the gear actuator, only. What happened for me is that my touch-n-go landings gave a little "bump" to one of the switches and caused this behavior to present itself. We were able to replicate the issue once the plane was on jacks. A few taps on the micro switch and the gear actuator would run just fine for several cycles. These switches can be cleaned, if that's the option some want to elect. 

I decided to replace them both given their age. Cost was roughly $90 each. Hope this is helpful information!

[N201MKTurbo]

Why did you send the actuator out? The inspection takes less time than packing and shipping it. There is no magic to doing it. It doesn’t take any special tools.

[Ragsf15e]

5 hours ago, TCW3 said:

For those of us flying vintage models, we expect a few parts to wear out here and there. I wanted to share a recent experience that resulted in an in-flight emergency as it could be simple, preventative maintenance for some. 

About a month ago, I went on the first flight following reinstallation of the gear actuator in my 1970 M20F. To comply with AD 75-23-04 I had to actuator removed, shipped to a Mooney Service Center, then reinstalled. All things checked out for the most part. The service center replaced a handful of parts that were worn, but nothing major - thank goodness the actuator passed and appears to have a lot of life ahead of it. 

To keep the story short, the gear failed to deploy on the return flight the first time I went up. I aborted the landing, went up for some altitude and spent some time troubleshooting before going through the emergency gear extension procedure. No gear down light, nor alignment on the visual window between the seats. Checked the circuit breakers (CB) and found the gear actuator CB to be tripped. This was odd because I did two touch-n-go landings before leaving the area with no issue.  And as far as the panel, the lights were working properly, which was very confusing when trying to troubleshoot. (Actuator test proved the bulbs weren't blown.) 

The meat of what I wanted to share for other owners: 

For the electric gear extension and retraction to function properly, there are two micro switches that work with the actuator. In the belly, attached to a rod, these two switches are in fixed positions. There is a plate attached to another rod that moves forward and back depending on whether the gear actuator is raising or lowering the gear. That plate, once at the right position, presses the button on the switch. For raising the gear, the switch turns on the Gear Up light and signals the gear actuator to stop. Same process for the other, but for the Gear Down light. Signaling to the gear actuator to stop is the important piece.

If either of these switches malfunction, the gear actuator won't know to turn off and instead trip the CB for the gear actuator, only. What happened for me is that my touch-n-go landings gave a little "bump" to one of the switches and caused this behavior to present itself. We were able to replicate the issue once the plane was on jacks. A few taps on the micro switch and the gear actuator would run just fine for several cycles. These switches can be cleaned, if that's the option some want to elect. 

I decided to replace them both given their age. Cost was roughly $90 each. Hope this is helpful information!

Thanks for your story.  Yes those switches can wear.  Probably wise to replace them.  Couple things to keep in mind too… on these old Dukes actuators, there’s no stop other than that switch and the circuit breaker. It’s possible (as just happened to someone else on this site) that the gear rods in the belly get bent before kicking the circuit breaker.  Might want to make sure yours are still straight.  Other thing is that (at least for my model’68F), pulling that cb is the first step of emergency extension.  That could be a cue before actually doing the manual extension.

Could you not see the lines painted on your floor indicator at all?  I’m interested and surprised if you couldn’t even without the light?

Thanks again for sharing.

[TCW3]

18 hours ago, N201MKTurbo said:

Why did you send the actuator out? The inspection takes less time than packing and shipping it. There is no magic to doing it. It doesn’t take any special tools.

A&P wasn't confident in replacing worn parts and proper re-assembly. For peace of mind, I went with the Mooney Service Center. 

14 hours ago, Ragsf15e said:

Thanks for your story.  Yes those switches can wear.  Probably wise to replace them.  Couple things to keep in mind too… on these old Dukes actuators, there’s no stop other than that switch and the circuit breaker. It’s possible (as just happened to someone else on this site) that the gear rods in the belly get bent before kicking the circuit breaker.  Might want to make sure yours are still straight.  Other thing is that (at least for my model’68F), pulling that cb is the first step of emergency extension.  That could be a cue before actually doing the manual extension.

Could you not see the lines painted on your floor indicator at all?  I’m interested and surprised if you couldn’t even without the light?

Thanks again for sharing.

The floor indicator was visible but lines were not aligned. I checked CBs prior to going through the manual gear extension procedure. I pressed it in once, and it popped within a few seconds given the switch malfunction. 

You are absolutely correct and hit the nail on why I'm sharing this: If these switches malfunction, the actuator will keep running and eventually trip the CB or bend your rods. Mine appear to be fine but I will have them rechecked at next annual. I do think whether the rods get bent is determined by the gear ratio for gears in the actuator itself. 

Those switches are cheap compared to the potential damage. Vintage owners beware. They're getting old!