Gear didnt come down.

[mhoffman]

Hey everyone,

 

Two nights ago i was inbound to KPDX and was on the ILS10 L when my gear didn't come down. After trying the gear switch a few times I ended up going missed and got vectored around while I tried to troubleshoot what was going on. After pulling the breakers and trying a few more times with the gear latch I ended up using the emergency extension and was able to get the gear down and flew the approach back in to KPDX and probably pulled off my best soft field landing i have ever done.

Now the weird part, so I got it to my mechanic in KTTD and he has not been able to reproduce the gear issue. Dropping the gear in multiple configurations he has yet to have it fail once. Has anyone else experienced something like this ? I have a 2007 Acclaim fwiw.

 

Thanks

Mike

[dkkim73]

@mhoffman An intermittent failure of the airspeed safety switch might produce those symptoms. One of the relays is in series with the landing gear circuit (in lieue of a squat switch). If you used the bypass button next to the gear lever, I believe that would have allowed it to go up... did you recall specifically trying that? These do go out from my experience and what I've read. 

Otherwise I would be thinking of something like a loose connector.  But that's very a nonspecific contribution. 

Edited January 16 by dkkim73
adding @ ref

[LANCECASPER]

1 hour ago, mhoffman said:

Hey everyone,

 

Two nights ago i was inbound to KPDX and was on the ILS10 L when my gear didn't come down. After trying the gear switch a few times I ended up going missed and got vectored around while I tried to troubleshoot what was going on. After pulling the breakers and trying a few more times with the gear latch I ended up using the emergency extension and was able to get the gear down and flew the approach back in to KPDX and probably pulled off my best soft field landing i have ever done.

Now the weird part, so I got it to my mechanic in KTTD and he has not been able to reproduce the gear issue. Dropping the gear in multiple configurations he has yet to have it fail once. Has anyone else experienced something like this ? I have a 2007 Acclaim fwiw.

 

Thanks

Mike

Good job on keeping a clear head and getting the airplane down safely with the gear extended. 

I always try to think about the simplest, thing that happens most often and it usually has to do with the gear latch. I know you verified it was latched, but I would check and clean the microswitch in there first. With all of the exercises you went through, breaker pulling, etc. it's going to be hard now to figure out exactly what happened.

(I flew back from KFTW to KSAT one night with the gear down 30 years ago because of not knowing about the gear latch. A passenger that I had dropped off must have kicked it on the way out of the airplane.)

[Danb]

Mike I did a few weeks ago actually about 4 times in last couple months but I got it down by putting the gear switch down many times..the MSC.changed the switch works great now..

[M20S Driver]

My Eagle did the exact same thing very intermittently and more on the colder days.  Long story but a few solenoids later, we fix it by replacing the gear down switch.

[dkkim73]

1 hour ago, LANCECASPER said:

I always try to think about the simplest, thing that happens most often and it usually has to do with the gear latch. I know you verified it was latched, but I would check and clean the microswitch in there first. With all of the exercises you went through, breaker pulling, etc. it's going to be hard now to figure out exactly what happened.

(I flew back from KFTW to KSAT one night with the gear down 30 years ago because of not knowing about the gear latch. A passenger that I had dropped off must have kicked it on the way out of the airplane.)

@LANCECASPER do you mean there's a switch that detects if the retention latch on the emergency gear handle is unsecured? Or just that if it's loose the mechanism won't work correctly. I'm looking at my POH and trying to work through your advice and anecdote. Thanks!

[LANCECASPER]

[mention=8122]LANCECASPER[/mention] do you mean there's a switch that detects if the retention latch on the emergency gear handle is unsecured? Or just that if it's loose the mechanism won't work correctly. I'm looking at my POH and trying to work through your advice and anecdote. Thanks!

Yes if the latch is not latched the gear will not go up or come down electrically

[mhoffman]

20 hours ago, LANCECASPER said:

Yes if the latch is not latched the gear will not go up or come down electrically

Greg at Advanced in KTTD thought it might be the Gear down switch starting to go bad but due to the fact he couldn't replicate the issue we dont have the definitive answer yet. We are going to get a switch and keep it in stock and keep our eyes on it and just hope it doesn't happen again. I did not know that about the emergency gear latch Ill check that micro switch on latch and give it a clean thanks for the heads up.

 

Mike

[peterl]

I had a similar experience with my Acclaim a couple of years ago. The gear occasionally did not come down and three maintenance shops were not able to solve the issue as it was difficult to replicate the failure. Numerous parts were cleaned and exchanged without solving the issue. Eventually an exchange of the gear up relay (!) made the difference.

[Danb]

1 hour ago, peterl said:

I had a similar experience with my Acclaim a couple of years ago. The gear occasionally did not come down and three maintenance shops were not able to solve the issue as it was difficult to replicate the failure. Numerous parts were cleaned and exchanged without solving the issue. Eventually an exchange of the gear up relay (!) made the difference.

I didn’t think the MSC wouldn’t be able to replicate my gear down issues but luckily it failed for them, had a gear down switch overnight and replaced. I feel more confident now going into the airport.

[dkkim73]

4 hours ago, Danb said:

I didn’t think the MSC wouldn’t be able to replicate my gear down issues but luckily it failed for them, had a gear down switch overnight and replaced. I feel more confident now going into the airport.

That kind of brings up an interesting point. If you had a loose contact and it got finicky in the flare, I guess the gear could come up. I don't recall any periodic switch inspection. Would be interesting to know how robust is the mechanism (I can see the headline now "Local pilot lands gear up after unecessarily monkeying with gear switch"). 

[Vance Harral]

19 minutes ago, dkkim73 said:

Would be interesting to know how robust is the mechanism

I got curious about this as well and looked in the schematics.  The gear selector switch is a DPDT switch, but the schematics for my 1976 M20F show only one pole being used.  Moving the switch simply routes a single +12V signal from the landing gear breaker, to one of two output contacts, that - after traversing some of the safety and indicator mechanisms - actuate the "gear motor up" or "gear motor down" relay.  It does seem like a single-point failure (broken internal switch guts, loose wire, etc) could command an opposite action from what the pilot selected.  It's probably not a very likely failure, and often simple is better.  But I'm still slightly surprised at the design.

[dkkim73]

3 hours ago, Vance Harral said:

I got curious about this as well and looked in the schematics.  The gear selector switch is a DPDT switch, but the schematics for my 1976 M20F show only one pole being used.  Moving the switch simply routes a single +12V signal from the landing gear breaker, to one of two output contacts, that - after traversing some of the safety and indicator mechanisms - actuate the "gear motor up" or "gear motor down" relay.  It does seem like a single-point failure (broken internal switch guts, loose wire, etc) could command an opposite action from what the pilot selected.  It's probably not a very likely failure, and often simple is better.  But I'm still slightly surprised at the design.

Tyvm for the detailed info and thoughtful comments; I was spitballing. I'm thinking of the split trim switch as an analog . If it's DPDT used as half (SPDT) you could always wire the halves in series. But that reduces the risk of an uncommanded action while increaseing the risk of a "no function" failure.

[mhoffman]

On 1/18/2025 at 3:39 AM, peterl said:

I had a similar experience with my Acclaim a couple of years ago. The gear occasionally did not come down and three maintenance shops were not able to solve the issue as it was difficult to replicate the failure. Numerous parts were cleaned and exchanged without solving the issue. Eventually an exchange of the gear up relay (!) made the difference.

Well bit of an update for today. Went to go for a flight and the gear decided not to come up this time, so im wondering if its the relay going bad. Will let you know what i find out.

[mhoffman]

Well finally figured out what the issue was. Looks like the gear motor is on the way out, it would intermittently work then not work depending on if it got smacked or not.