Landing gear panel light inop

[Sime]

So I just got my 76 M20F back from it's annual and when I came in to land, the 'gear down' light on the panel wasn't illuminating, however the visual sight window on the floor was showing the gear down and locked (green). Landed safely and gear is stable. When I press the annunciator test button, the 'gear down' light successfully illuminates green.

I checked the only limit switch (I could find) in the left landing gear well, and there is a 1-2mm gap between the end of the switch and the plate attached to the gear that appears to actuate the switch. I actuated the switch manually ten times but the light is still not on. Is this switch supposed to be open when the gear is down?

My A&P is away overseas for work for 2 weeks. As the gear indicator between the seats is the primary indicator and that is functional, is the aircraft airworthy without the panel (convenience) light illuminating? If so, I would like to take the aircraft up and cycle the gear several times to see if this fixes the issue.

Any other ideas to check?

Thanks in advance,

Sime

[Hank]

The only other way to check it is with the plane on jacks. But that makes the switch hard to see with gear up. Raise the gear then do a partial Emergency Gear Extension and check the switch position. Electrical contact cleaner is about $10 at your auto parts store; soak it down good, exercise the gear a couple of times, soak it down again. Spray liberally.

Beyond that, I'm out of ideas other than checking with an ohm meter or getting professional help.

[N201MKTurbo]

Do you have a Johnson bar?

oh 76 never mind. 

The limit switches are on a rod by the actuator in the belly.

Edited April 21, 2018 by N201MKTurbo

[Sime]

Thanks gents.

So is the aircraft un-airworthy with the panel gear down light inop?

[N201MKTurbo]

Check if your nav  lights are on. It will dim the gear down light.

[Marauder]

Thanks gents.
So is the aircraft un-airworthy with the panel gear down light inop?

The floor indicator is mechanically connected to the tubes that move (I believe) the nose gear. The light verifies by the position of the switches.

I can’t/won’t advise you whether it is okay to fly. That’s your call. I did however experience a failure of the floor indicator once and elected to fly the plane 200 miles back home. In this case, the indicator’s plastic slider broke in the gear down position despite the light saying it was up. I could tell from my speed it was up. When I got home I was able to get the gear down light and feel the movement so I was certain it moved.

Have you pulled the light out and try reseating it? Sometimes weird stuff happens like you described.


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[N201MKTurbo]

1 hour ago, Sime said:

Thanks gents.

So is the aircraft un-airworthy with the panel gear down light inop?

If you are a stickler for the rules, it is not airworthy.

leagely you will need a ferry permit to fly it somewhere to get it fixed.

The chance of getting in trouble for it are very low. 

You have to make your own decisions.

[Vance Harral]

We have a '76F model too, presumably wired the same way as yours.  I have the electrical schematics for it, PM me if you're interested in a copy.

Assuming our airplanes are wired the same way, the switch you found in the wheel well is the "squat switch" that prevents the gear from being raised when there is weight on the wheels.  It's normal for there to be a small gap between the switch and the plate when the airplane is on the ground - that's how it works.  When you take off and the gear doughnuts expand, the plate moves to close the switch.  The switch is actually a double-pole switch which routes power to one of two different sources when the gear selector is in the up position.  If the squat switch is "closed", power is routed to the gear motor to raise the landing gear.  If it's "open", power is routed to the gear warning horn instead.  This is something I think a lot of people don't know - that there are actually two logical events that cause the gear horn to sound.  Reducing throttle below the switch point with the landing gear up is only one of them.  The other is attempting to raise the landing gear with weight on the wheels.

Anyway, the squat switch has absolutely nothing to do with the green "Gear Down" and red "Gear Unsafe" lights on your panel.  Those lights are controlled only by the limit switches in the belly.  Those limit switches are also DPDT switches, meaning they have two independent switch circuits in a single housing, actuated by a single "button".

Since you're able to get the "Gear Down" light to illuminate with the push-to-test switch, the problem has to be the down-limit switch in the belly.  The external switch "button" and the internal half of the switch which controls the gear motor itself must be working - otherwise the gear motor would not have stopped running when you selected gear down, and the gear motor breaker would have tripped.  So it's highly likely the half of the switch that controls the gear down light is the problem: either the internal guts of the switch have failed, or (hopefully) the wire connections to it have simply come loose.

As owner/operator, you're absolutely allowed to remove the belly panel that allows you to look at the limit switches.  If you find one of the wire terminal connections associated with that switch to be loose or disconnected, you can try wiggling it against the terminal it's supposed to be connected to, and I'd bet that will cause your green "Gear Down" light to illuminate.  What you do beyond that is up to you - let your conscience be your guide.  I think we all know the letter of the law.  From an actual safety perspective, I draw a distinction between, say, an electrical engineer who has the schematics for the aircraft, a voltmeter to test the switch, and the experience to use both; vs. someone who just grabs a bottle of contact cleaner and uses the "spray and pray" approach.

[Guitarmaster]

So I just got my 76 M20F back from it's annual and when I came in to land, the 'gear down' light on the panel wasn't illuminating, however the visual sight window on the floor was showing the gear down and locked (green). Landed safely and gear is stable. When I press the annunciator test button, the 'gear down' light successfully illuminates green.
I checked the only limit switch (I could find) in the left landing gear well, and there is a 1-2mm gap between the end of the switch and the plate attached to the gear that appears to actuate the switch. I actuated the switch manually ten times but the light is still not on. Is this switch supposed to be open when the gear is down?
My A&P is away overseas for work for 2 weeks. As the gear indicator between the seats is the primary indicator and that is functional, is the aircraft airworthy without the panel (convenience) light illuminating? If so, I would like to take the aircraft up and cycle the gear several times to see if this fixes the issue.
Any other ideas to check?
Thanks in advance,
Sime

Does the light in the floor indicator come on?

Did you have the nav lights on?

If the floor indicator light came on, and you had the nav lights on, and you got no green light than your problem is in your nav light circuit. Usually a broken resistor or diode in this case.

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[carusoam]

Summary..?

1) problem: the gear down light isn’t going on...

2) did you check the bulb? It is designed to easily swap out with the one in the gear up position... (for some reason)

3) The electrical diagram is resident in the POH...

4) The switch for gear position could be at fault... is it one switch? One position is on for GU, the other position is on for GD? There won’t be a way to turn one light on without turning the other off...

5) Wait a minute.... You are familiar with the iris lenses on these wonderful analog 60s devices aren’t you?  Twist the iris open to see the light going on behind the iris...   

6) Do you have an anunciator or the two old style iris lights...?

 

If this saves you from calling the mechanic, send the donation check to MS... 

Best regards,

-a-

[Yetti]

This is an on the ground fix thing.  Probably be familer with proper jacking.  Limit switches and contact cleaner and lots of belly screws. 

[Sime]

Thanks all. I'll remove the belly panels and have a nosey around to see if the issue is obvious. If I can't see anything, I will have my A&P friend who did the (recent) annual have a look at it. He has the correct jacking pads for the Mooney and is familiar with jacking/supporting it correctly. He should be back in a little over a week.

Will report back with my findings.

Cheers,

Sime

[Sime]

I have managed to get the light to function now! Looks like the landing gear horn breaker popped. I didn't see it because my iPad ram mount was covering it. Resetting the breaker has resolved the issue.

It must have blown due to one of two things. 1/. I think I read somewhere that the 12v auxilliary port is wired to the same circuit as the gear warning horn/light. The Ipad charger cable may have grounded out on the yoke during my last flight. Or 2/. the gear warning horn was replaced at annual. I'll check the wiring to see if it has shorted or perhaps the warning indicator itself is faulty?

Appreciate all your assistance on this!

[Yetti]

The standard issue 12v cig lighter plug is on the ignition switch circuit in the 75 F   Probably the same for the 76.  I believe the gear warning horn is on another 2 amp  breaker next to the landing gear.

It's page 2-13 of my PoH.  

You may have wires rubbing together, but I don't think they are the ones you are thinking they are.   Might be the gear warning horn did not get properly installed