Strange buzzing in gear warning system after T/O

[Mark89114]

After gear is up there is a strange bzzzing noise coming from the gear warning system, all of the lights are off, floor indicator looks good.  It bzzzes for about 20 seconds, it isn't a full on alarm, just barely like a microswitch or something isn't all the way open/closed somewhere.  The noise does go away pretty quickly.  I identified it as being the gear warning system as I pull the gear warning CB and it stops, push it back in and there it is.  I assume it is some of the microswitches in the belly or maybe the microswitch on the throttle position?, but before I get my mechanic involved in a full on diagnosis want to give him some clues what to look for.

Thank you and stay safe everybody.

Mark           

[Hank]

Welcome to winter, Mark!

In colder weather, the pucks expand slower and don't hit the limit switch, resulting in the buzzer. Once they expand, it should stop.

Check your Service Manual, jack the plane and do the puck movement test. My guess is that you will be borderline on this.

[Mark89114]

I might buy the cold weather theory, but I don't think there are any limit switches in the wheel well to sense retraction?  I think they are all in the belly on the pushrods and what not.  I don't know what the limit switches are measuring or commanding to do or not do.  Also not 100% sure related to cold weather has it has been going on for a while, just assumed it was one of those random airplane noises that occur as it sounded like feedback through the audio system.  

The airplane just came out of annual by a well known MSC and I don't think my pucks are ancient, but apparently on the long bodies they have a much more limited life, but my landings are all smooth as silk so no abuse there......

 

[PT20J]

No idea if this is related, but I did run across this Service Instruction a while back.

sim20-103.pdf

 

[carusoam]

Hmmmmmm...

Have to think about that one....

1) Long Body

2) After T/O

3) after gear is stowed

4) Power, WOT

5) No issues with the gear stowing

6) No obvious issues with...

• Stall vane
• Throttle switch
• Air speed switch, no squat switch
• Electric fuel pump

These are things that can be related to sounds heard in the cabin...

The fuel pump in the R is automated... at WOT the pump is running...

Did the sound stop while pulling back on the power?

PP thoughts only, not a mechanic...

Best regards,

-a-

[Mark89114]

A,

the sound goes away when I pull the gear warning CB.  It also goes away on its own about 20 seconds after TO power application and the gear is solidly retracted, I can't hear it during the takeoff roll, again it is very faint, not a full blown warning horn.  The horn works normal when gear is retracted and power is pulled to idle.  

Mark   

 

[Yetti]

In my Kuboto Tractor it means the hydraulic level is low

[carusoam]

If and only if... I recall correctly... (highly unlikely)...

Somebody reported a similar issue... with the cause being something else was leaking power (probably nearby)...

The leak was then grounding through the gear horn...

1) You have verified where it is grounding through... by pulling the CB for the gear horn...

2) now to find the source of the extra electrons... this may be possible by pulling all the other CBs... (?) while on the ground would be best for this activity!  
 

Probably not enough to go on...  hopefully enough to spark somebody else’s memory... 

Having the electrical diagrams may be helpful for review... to see what else would be likely to accidentally dump power to that circuit...

Go crowd sourced problem solving!

PP thoughts only, not a mechanic...

Best regards,

-a-

[ArtVandelay]

A,

the sound goes away when I pull the gear warning CB.  It also goes away on its own about 20 seconds after TO power application and the gear is solidly retracted, I can't hear it during the takeoff roll, again it is very faint, not a full blown warning horn.  The horn works normal when gear is retracted and power is pulled to idle.  

Mark   

 

Try disconnecting the switch.

If it goes away your switch needs to be replaced, if it doesn’t you have a short somewhere in the wiring.

 

Obviously you’ll need to take extra care not to forget the gear when you do this test, don’t be distracted and do something stupid.

[Mark89114]

I sprayed contact cleaner all around and in the microswitch, best I could.  So far one flight and it didn’t reappear.  Will keep an eye on it.

[Mufflerbearing]

Could it be the stall warning?  Mine is very hyper as soon as I take off and when I get a little more speed, it quits.