Gear problem

[flyby201]

I was out on a local flight a few days ago, when I returned to the airport and went to ower the gear I activated the switch but nothing happened.  Called the tower and told them I was turning east to diagnose the situation and lower the gear manually if necessary.  About the time I completed my turn I glanced over and noticed and noticed that the GEAR ACT circuit breaker was tripped.  I reset it, gear came down and I landed normally.  I do not know at what point during the flight the CB tripped.

Yesterday, my A&P and I jacked it up, swung the gear several times but could not recreate the problem.  We verified the manual system was functioning properly just in case.

I just installed a new Concorde battery and this was the second flight with it.  I checked voltages during the above flight and they were in the 14.1 to 14.4V range, so it doesn't appear to be an overvoltage problem.  My yoke mounted Garmin 295 was acting upend during this flight.  Kept shutting itself off.  It's wired into the avionics master.  I eventually unplugged it at the GPS end.e a

Anyone have an idea of what may have caused this?  I hate to throw money at this, not knowing the true cause, but it could be a potentally serious situation.

[KSMooniac]

My guess would be the gear motor itself.  If yours is original it might be long in the tooth and prone to not working if it stops at a certain orientation.  Mine failed in 2008 in a similar fashion, but the CB didn't pop and I had to crank my gear down.  I'll also advise that you thoroughly check your manual gear system as it could be mis-rigged such that it won't engage properly and you'll end up with the gear stuck up in the well.  That is a single point of failure that Bruce Jaeger showed me when I was up there getting my tanks resealed, and he said I was fortunate that it worked as designed.  (It failed on my way into Wilmar.)

Other steps you could take are checking all of the wires for corrosion at the terminals, or loose connections or even failed wires at the terminals.  You might get lucky and find something there creating a lot of resistance that culminated in the popped CB.

[DaV8or]

In addition, I might check any limit switch rigging there may be. Something tells the motor to shut off when the gear is all the way up and if this switch is defective, or improperly rigged, the motor will fight against solid metal and the end result will be a popped circuit breaker. The same thing happed to my old garage door opener.

[butchgilbert]

Agree with DaV8or, check the limit switches, this happened to my flap motor a while back, easy fix if you can find it.

[flyby201]

Thanks all.  We checked for any runaway limit switch type problem yesterday and it all checked out ok.  I'll have to check back thru the logs, but I'm pretty sure gear motor has been overhauled, but how long ago I don't know off the top of my head.  Will check tonight.

[Vref]

Quote: flyby201

Thanks all.  We checked for any runaway limit switch type problem yesterday and it all checked out ok.  I'll have to check back thru the logs, but I'm pretty sure gear motor has been overhauled, but how long ago I don't know off the top of my head.  Will check tonight.

[DaV8or]

Quote: Vref

check out the CB itself also if it trips a set load!

[flyby201]

Quote: Vref

check out the CB itself also if it trips a set load!

[jetdriven]

You can hook it up to a battery on the bench and use an ammeter and a shunt with a potentiometer to test it.  But the cost of a 7277 CB is only around 25$ so its just as easy to replace it as there is to test it.

 

We have the same Dukes actuator you have. I just disasembled and inspected it.

 

SB M20-112 says

1. 
   
2. 
   

   Extend and retract the actuator against an 800 pound peak end opposing load (or aircraft landing gear if installed). Operating time shall be 9 seconds maximum, and current drain shall be 25 amperes maximum, at a stroke of 3.0 inches. (Available stroke is 4.61 ¦ 0.03 inches.)

   
   
   

[docket]

I had the problem with mine where it was tripping the breaker and, believe it or not, it was the light that supplied light to the gear up indicator in the floor.  It would intermittently blow.  After we took the belly off the plane we found that the wire going to the light had a little chafe.  Replacement of a few feet of the wire and problem solved. It was annoying until we diagnosed it.

[jwilkins]

It may sound silly but the easiest way we found to test breakers is to replace them if suspect. We always used to try to replace the breakers with the ones that could be pulled to open the circuit, even if the original was a trip-only version. 

The regular (not the switch / breaker combo) breakers are not expensive and , although they are usually a *pain* to R&R, replacing the breaker automatically checks for tight connections, too. If you do R&R a breaker make sure you take a minute to clean up the terminal and inspect for a good crimp on the wire. A light wipe of dielectric grease on the terminal is not a bad idea, either.

Jim

 

[flyby201]

Still have not found the cause of the CB tripping.  Following the first flight we put it up on jacks and swung the gear 8 or 10 times and it worked just like it was supposed to, no problems.  The next flight my CFI/A & P was with me doing an IPC.  It worked perfect on that flight.  Next flight we were shooting a bunch of approaches and raised and lowered the gear 8 or 10 times and it tripped the CB every time.   We did get more information on when it was tripping.  When the gear is retracting, the low voltage annunciator light would flash 4 or 5 times and then the CB would trip.  I thought for sure that we would find the cause once we got back on the ground and got it up on jacks as it was doing it every time now.  Well, we got it up on jacks and, you guessed it, it worked perfectly.  I did look at the light for the indicator on the floor.  That light is not working, but I couldn't see any problems with frayed wires or anything.  I assume, maybe incorrectly, that that light is controlled by the panel light dimmer switch.  We also noticed that the "Gear Unsafe" indicator light does not illuminate while the gear is travelling up or down, is it supposed to?  We did test the bulb inside it and it worked when tested.

With this new information I tend to believe the CB itself is still good.  Something is going on to cause the voltage annunciator to flash and whatever that is is causing the CB to trip.  Of course, it would be a big help in diagnosing the problem if we could make it happen in the hangar.

[DaV8or]

At this point I might start to suspect low voltage as the culprate. Low voltage = high amperage. When you test the gear on the ground, do you do it with all the radios and lights on? If your generator/alternator can't keep up, a low voltage situation could cause your gear CB to trip.

[jetdriven]

The gear actuator could have very high amp draw, causing the low voltage and CB to trip.  When is the last time the gears were inspected and greased?  IIRC Mooney suggests this gets done every 200 hours.  In ours, we raised and lowered the gear dozens of times in the hangar on the battery.  It never tripped the CB.

[Lionudakis]

The other thing that swinging a gear does not take into account is additional g loads while climbing and sucking the gear up, and vibrations induced into the wiring (chaffing), in addition to jetdrivens recommendation with good ol lube, I'd check the motor. 

High amperage causes low voltage, if you run out of available amperage due to a high amp draw.  

[Kwixdraw]

Check for  a short in the gear switch wire loom behind the radios. I had one back there some years ago that would pop the breaker only during climb out gear retraction. Would cycle normally in level flight.