Intermittent Gear Warning C/B pop

[Av8rjm]

1986 Mooney M20J

I am new to MS, so hello all!

I am lucky enough to have a Dad that bought a Mooney a few months and he lets me fly it, but the gear warning circuit breaker has started to intermittently trip after the gear is down and locked. Sometimes, everything works as intended, but if it trips, it resets fine. Of course, each time my A&P/IA and I think we solved it, it trips again. We think it may be a loose wire or a bad breaker. Annual is in September so I would like to see if there are any high failure points I can talk to my IA about that may be Mooney specific.

Here is some context:

We have an LHS-200C, which is wired into the "Gear Down" annunciator light. The breaker still pops when this system is powered off/ its breaker is pulled.

Breaker does not pop when testing the annunciator panel

It seems to not pop at lower RPM. Maybe less vibration?

This only happens after the gear is down and locked, sometimes multiple seconds after it is down and locked.

 

Any and all help is appreciated,

Thanks!

Josh

 

 

[Ragsf15e]

1 hour ago, Av8rjm said:

1986 Mooney M20J

I am new to MS, so hello all!

I am lucky enough to have a Dad that bought a Mooney a few months and he lets me fly it, but the gear warning circuit breaker has started to intermittently trip after the gear is down and locked. Sometimes, everything works as intended, but if it trips, it resets fine. Of course, each time my A&P/IA and I think we solved it, it trips again. We think it may be a loose wire or a bad breaker. Annual is in September so I would like to see if there are any high failure points I can talk to my IA about that may be Mooney specific.

Here is some context:

We have an LHS-200C, which is wired into the "Gear Down" annunciator light. The breaker still pops when this system is powered off/ its breaker is pulled.

Breaker does not pop when testing the annunciator panel

It seems to not pop at lower RPM. Maybe less vibration?

This only happens after the gear is down and locked, sometimes multiple seconds after it is down and locked.

 

Any and all help is appreciated,

Thanks!

Josh

 

 

Welcome to MS!

Sometimes these kind of intermittent failures are the hardest to solve!  The cb may indeed be bad, however, that’s a weird one to fail.  Have you tested the gear warning system to see if it works?  At altitude, with gear up, pull throttle to idle.  You should get a gear warning horn.  There’s a switch that activates when the throttle is around 13” or less.

[Av8rjm]

15 hours ago, Ragsf15e said:

Welcome to MS!

Sometimes these kind of intermittent failures are the hardest to solve!  The cb may indeed be bad, however, that’s a weird one to fail.  Have you tested the gear warning system to see if it works?  At altitude, with gear up, pull throttle to idle.  You should get a gear warning horn.  There’s a switch that activates when the throttle is around 13” or less.

The gear warning system works, the horn sounds when the manifold pressure is below 12”-13” and the breaker does not trip. It seems to only trip after the gear is down and locked.

I have a vague memory of reading how the system works and thought that once the gear is down and locked, the circuit with the warning horn is open, if I remember that correctly, I could probably rule that part of the system out. But, like I said, that’s a vague memory so I may be wrong.

[Fly Boomer]

17 hours ago, Av8rjm said:

This only happens after the gear is down and locked, sometimes multiple seconds after it is down and locked.

First thing that comes to mind is that the gear actuator may not be powered off when the limit switch says the gear is down.  Could be bad or dirty switch, or could be adjustment.  Can you hear the actuator stop when the gear clunks down?

[PT20J]

1 hour ago, Fly Boomer said:

First thing that comes to mind is that the gear actuator may not be powered off when the limit switch says the gear is down.  Could be bad or dirty switch, or could be adjustment.  Can you hear the actuator stop when the gear clunks down?

That would pop the gear actuator breaker rather than the gear warning breaker. 

[PT20J]

If I were troubleshooting this, I would begin by disconnecting the LHS from the gear down annunciator. If the fault is in the LHS or its wiring, powering it down would likely have no effect on the gear warning circuit because they are separate circuits. 

[Av8rjm]

15 hours ago, PT20J said:

If I were troubleshooting this, I would begin by disconnecting the LHS from the gear down annunciator. If the fault is in the LHS or its wiring, powering it down would likely have no effect on the gear warning circuit because they are separate circuits. 

That makes sense, I’ll try that next time I’m flying and will update. Thank you

[JModelDave]

One thing to check is to see if the light socket on the gear light for visual indicator in the floor may be shorting intermittently. We just ran into a very similar problem on a K-Model at our shop and it turned out to be a bad gear down limit switch. It should also be noted that the gear rigging should be checked ( which requires special tooling) if the switch is changed. We check the gear rigging on Mooneys at annual at our shop. 

[ajudson]

I had a similar problem with my '87 J. After troubleshooting with a few different mechanics, a new gear limit switch (didn't help), and nearly 10 hours of labor put into the issue, my A&P finally traced it to a rubbed/burned-through portion of the wires that was shorting during flight. It was also intermittent during flight. It's a tricky one to find, but I'm happy the breaker hasn't popped since! Not sure it was worth the AMUs I put into solving it though....

Edited August 6, 2023 by ajudson

[hubcap]

I would start by replacing the circuit breaker. I had one go bad on my 82 M20K.

You will drive yourself crazy trying to find the problem if it is the circuit breaker.

[Av8rjm]

New update:

I went flying yesterday and noticed that the gear down light flickered intermittently. But, the breaker did not trip. It mainly occurred when I extended/retracted my speed brakes. Is this a symptom or a coincidence? Unfortunately I have not been able to troubleshoot because my job has been keeping me busy.