Uncommanded co-pilot seat release

[Oldguy]

For the last week, my '84 M20J has been acting like a Cessna with the co-pilot seat. At various times - with no discernable pattern - it will slide from a locked position all the way back. The person sitting there has been a CFII and not handling the controls, but it is not an acceptable situation. He slides the seat forward prior to take off, tries to move it back and forth (AKA the Cessna seat shake) and it seems locked in position, but at some point it slides all the way to the rear during the flight. Checked everything from him accidentally bumping it with his heels to not really being locked but have come up blank.

 

The only thing done to the seat in the past few weeks was to raise it up so my wife could see over the glare shield. I have even tried cranking it back down, but am getting nowhere. Nothing appears to be broken in regards to the retaining pins on the seat rails or springs in the locking mechanism. While some of the seat rail holes are somewhat oval but do not appear different from the week before, every position he tries yields the same, so I am leaning more towards something in the seat mechanism itself.

 

Does anyone have any suggestions? Any and all help is appreciated.

 

Thanks,

John

[orionflt]

John,

take a look at the holes in the seat track, they could be filled with dirt keeping the pin from fully seating. I had this happen to me when I first got my aircraft, get in there with a scribe and vacuum to clean them out. I was surprised how much dirt was packed in there and the holes looked pretty clean when I initially looked at them. I also added a second spring to the pin mechanism helping to keep the pin locked in place.

 

Brian

[clh]

I don't know, but take a look at the rollers on the seat. if the rollers are worn, could it allow enough slop for the pins to clear the holes? 

[Oldguy]

John,

take a look at the holes in the seat track, they could be filled with dirt keeping the pin from fully seating. I had this happen to me when I first got my aircraft, get in there with a scribe and vacuum to clean them out. I was surprised how much dirt was packed in there and the holes looked pretty clean when I initially looked at them. I also added a second spring to the pin mechanism helping to keep the pin locked in place.

 

Brian

Brian,

 

Thanks for the tip. I'll check them out and see how they look.

 

I hadn't thought about a second spring. May be something I look at if no joy with the cleaning.

 

John

[Oldguy]

I don't know, but take a look at the rollers on the seat. if the rollers are worn, could it allow enough slop for the pins to clear the holes? 

Could be. Make me think maybe I should look at both sides if one is worn. Worth checking out.

 

Thanks.

[N201MKTurbo]

so, warn rollers would let the locking mechanism sit closer to the holes and would lock it better. If the fingers on the aluminum blocks that go on the rails were worn or the bottom edge of the rail was warn it could let the block raise up enough to disengage, but unlikely. Make sure all the rail blocks are actually engaged in the rails. This usually happens when installing the seat.

 

I like the dirt in the holes theory, or else something is broken. I guess the pins could be worn.

 

In thirty years of Mooney ownership I've never had this happen.....

[Will W]

This is a common topic at MAPA safety seminars, it's usually dirt in the tracks. Take a look and see what's under there and you can usually clean it out yourself but you got to get a drill bit in your hand and start twisting it out.

[furledd]

I second the drill bit check

 

I ran one of the correct size very slowly down my pilot seat lock holes and bumped the power very slowly a few times and a bunch of dirt augering up and out of most of my holes a couple weeks ago. 

[Yetti]

When I had my seats out to put on the new seat belts, I noticed the rear rollers were more worn than the front, so I rotated them. Should help the seat from dragging.  A .250 drill bit will clean out the locking holes will probably help,

[kortopates]

Besides cleaning out the holes, don't rely on the springs to push the pins into the holes - make sure the seat occupant positively pushed the lever down as well to ensure the pins are seated, if the holes are overly rounded then the rails should be replaced just like Cessna rails. They are available from Mooney. 

[Oldguy]

Okay, resolution found.

 

As several recommended, I cleaned the holes out and removed an 1/8" or more of dirt and gunk (the technical term) from under the hole. In addition, the inboard rail has a very deep gouge where the pins have not been lifted when moving the seat forward to the rear-most hole. Between the "lift" provided by the buildup under the rail and the trench leading up the the first hole, it slips out if the right pressure is put on it. Quick solution is to latch the seat in the second or further to the front hole with the long term solution to replace both rails as Paul suggested. And with a little over 5100 hours on the plane, I will probably look at doing both rails on both seats. Rather pay that price than the one that comes with a seat slide on takeoff.

 

Thanks to everyone for their suggestions.

 

John

[jetdriven]

Lasar also sells new delrin seat rollers which help the pins clear the holes when moving the seat. About 60$ iirc

[Yetti]

Hmm I was thinking as I was rotating mine that some Acetal rod and a little work I could have some new ones.    $4.22 for a foot of materials.  If you don't have a lathe, I would think mounting them on a drill and a round file would have some new ones in no time.

[gsxrpilot]

After the news about the lawsuit in CA because of this very thing, it got me thinking what I would do if it happened to me in the Mooney, on takeoff, possibly solo. I've discovered with the seat all the way back, I can still reach the center steel member from the panel to the roof. I'd grab on to that and can hold myself forward enough to fly the plane and get it back on the ground.

[juanM20J]

That is exactly what I had to do the first tie that occurred to me 2 weeks ago (July 2023)  Since then , removed the seat, cleaned the wholes, re-installed the seat and yet:  problem remains  my seat is not locking properly   Rail track holes or wheels do not look too worn - Will double check if the rear wheels are more worn than the front ones which could make the seat's front position be slightly lifted thus making the pins not go deep enough

 

[A64Pilot]

On 3/28/2015 at 7:41 PM, Yetti said:

Hmm I was thinking as I was rotating mine that some Acetal rod and a little work I could have some new ones.    $4.22 for a foot of materials.  If you don't have a lathe, I would think mounting them on a drill and a round file would have some new ones in no time.

Someone made me some that were flat, and work perfectly. I think maybe that concave shape may come from wear?

[M20F]

Carpeting strands can block the hole as well.  The carpeting in that area tends to get frayed in the older birds and it causes it not to lock, not to move, etc.