Landing gear breaker tripping

[mikebroady]

I have a 1976 M20F and have experienced two incidents with breakers tripping when operating the landing gear. First was back in Feb doing circuits and on the last (6th) circuit just after climb out and  retracting the gear we noticed a slight burning smell which I put down to maybe the front tyre rubbing or not tapping the brakes properly. I think I noticed a whirring noise too but the cockpit is so noisy I couldn't be certain. A few seconds later the low voltage light illuminated and I noticed the main breaker had tripped. Once reset all was ok and the gear let down with no problem.  

2 more flights, 5 landings and no repeat of the problem. A 50hour was then carried out but the problem could not be replicated and checks found nothing. It also happened once back in 2012 on downwind so I didn't think the chances were high of finding the cause.

I've flown 7 times now with no issues then on the 8th flight on Thursday lowering the gear tripped the landing gear breaker. The manual indicator showed the gear was down ok but the unsafe gear light was illuminated. I climbed out to give time to assess and investigate but resetting the breaker solved the issue; the gear retracted and lowered ok.

The three events may well not be connected. I'm no mechanic so any advise would be grateful as I believe there's always a reason for a problem.  I've spent a little time checking on the forum and note a couple of issues may have some bearing. I've added an old pic of the panel to show the gear switch and breaker panel.

First, I need to check the manual gear handle has not been inadvertently caught and out of position but I think I would have probably noticed this.

Gear grease may be old, so I'll check with the engineer.

My discs could probably do with changing but not sure if that would affect lowering of the gear.

Could it be a relay sticking or switch problem causing the gear motors to continue trying to operate perhaps until the load tripped the breaker?

Mike Broady.

[ShuRugal]

Get your mechanic to give it a thorough checking. Low voltage alarm followed by a popped breaker indicates something is binding and overloading the gear motor.

I don't know what your alternator/generator is rated at, but for the gear motor to drag your system voltage down far enough to get an alarm, it's drawing a few hundred watts. Mooney landing gear is very simple and designed to be operated by hand - there is no way that much demand should ever be placed in the motor.

Good idea about the limit switches. If one is slightly out of place, that might result in an intermittent overrun condition?

Either way, you need someone with experience working on Mooney landing gear to put hands on it before you do permanent damage to the motor/drive.

[Ragsf15e]

I might also check the gear motor CB.  Especially if this happens after several cycles.  That CB getting old may increase resistance, heat, etc and fail.

Old grease or something catching/binding might be even more likely, but the CB can’t be ruled out.

Ive had issues with my limit switches, but they didn’t give me electrical indications like lower voltage or popped breakers.  The gear just didn’t move when i moved the switch.  About 10” later, it moved normally.  Lubing the switches with LPS1 seemed to help.

With a ‘76, do you have an airspeed switch or a squat switch?  Gear pucks (discs) shouldn’t be causing what you described.  If you have an airspeed switch the gear pucks don’t play in gear issues.  With a squat switch, old pucks or a poorly positioned switch can cause gear to fail to retract.  This usually happens in cold weather when the pucks remain compressed after takeoff.  Doesn’t seem like your problem.

 If you have a squat switch it’s a small weight on wheels sensor in left wheel well.  Airspeed switch is a brass colored thing behind your airspeed indicator.  Neither of these seem part of this problem.

[mikebroady]

Fully intend to but always useful to go with any info/experience from the MS community. I'm not convinced the main breaker trip 8 years apart is the same issue as the recent landing gear breaker trip but you never know. As regards a Mooney landing gear "expert in the UK" I doubt one exists! I have to trust the guy's at Liverpool who have looked after it for the 12 yrs I've owned her unfortunately.

[MikeOH]

Just now, mikebroady said:

Fully intend to but always useful to go with any info/experience from the MS community. I'm not convinced the main breaker trip 8 years apart is the same issue as the recent landing gear breaker trip but you never know. As regards a Mooney landing gear "expert in the UK" I doubt one exists! I have to trust the guy's at Liverpool who have looked after it for the 12 yrs I've owned her unfortunately.

Maybe call Don at Maxwell, or Mark/Tom at Top Gun?

[mikebroady]

7 minutes ago, Ragsf15e said:

I might also check the gear motor CB.  Especially if this happens after several cycles.  That CB getting old may increase resistance, heat, etc and fail.

Old grease or something catching/binding might be even more likely, but the CB can’t be ruled out.

Ive had issues with my limit switches, but they didn’t give me electrical indications like lower voltage or popped breakers.  The gear just didn’t move when i moved the switch.  About 10” later, it moved normally.  Lubing the switches with LPS1 seemed to help.

With a ‘76, do you have an airspeed switch or a squat switch?  Gear pucks (discs) shouldn’t be causing what you described.  If you have an airspeed switch the gear pucks don’t play in gear issues.  With a squat switch, old pucks or a poorly positioned switch can cause gear to fail to retract.  This usually happens in cold weather when the pucks remain compressed after takeoff.  Doesn’t seem like your problem.

 If you have a squat switch it’s a small weight on wheels sensor in left wheel well.  Airspeed switch is a brass colored thing behind your airspeed indicator.  Neither of these seem part of this problem.

Not sure but I think it's an airspeed switch. The thing is the landing gear lowered fully,  confirmed by the floor indicator, so that's why I thought it could be a sticking relay perhaps.

[charlesual]

There’s a service bulletin for 20:1 gear actuator. (My 67 F is 20:1. Not sure about 75F) Supposed to remove/inspect gear actuator and re grease with specific grease. The solution is to retro with a 40:1 gear. Lasar has them for $1500. I’d love to source one for cheaper but hard to find.


Sent from my iPhone using Tapatalk

[mikebroady]

4 minutes ago, charlesual said:

There’s a service bulletin for 20:1 gear actuator. (My 67 F is 20:1. Not sure about 75F) Supposed to remove/inspect gear actuator and re grease with specific grease. The solution is to retro with a 40:1 gear. Lasar has them for $1500. I’d love to source one for cheaper but hard to find.


Sent from my iPhone using Tapatalk

Not sure either so I'll ask them to check. Having ploughed through the manual I see there are gear up/down limit switch striker arms (but no illustration of the switch) and a tolerance from  the bumper pads. Maybe if this is incorrect it could mean the motor running on after the cycle has completed causing the breaker to trip.

By the way, if anyone knows who is responsible for Windows 10 theyhavemypermissiontoshootthem!!! That's what my keyboard is now doing following yet another out of the blue mid sentence shut down-god I hate it.

[squeaky.stow]

Hi Mike,

When a CB trips, your airplane is trying to warn you that something is wrong. When the main breaker (I assume you mean the battery bus) trips, your airplane is screaming that something is wrong. That is one big breaker. Combined with the burning smell you have a serious warning that you could be at risk of an electrical fire in flight. There are not many airborne emergencies that are worse than an electrical fire. It can go from “sniff sniff- what’s that?” to really ugly in seconds.

Not trying to lecture. Just concerned for your safety. The Mooney POH doesn’t have much to say about resetting tripped CBs in flight but most airlines forbid it unless absolutely critical for the safety of flight. I would not fly your airplane again without determining the cause of the tripped CBs and ensuring that there was no damage to the electrical system. I have had the gear CB trip once in my airplane. I left it out, lowered the gear manually and landed. My AME found that my actuator was in need of an overhaul but that did not fully solve the problem. Further investigation revealed a bad cannon plug with corroded and burnt contacts. 

Good luck with the diagnosis.

 

[Ragsf15e]

7 minutes ago, squeaky.stow said:

Hi Mike,

When a CB trips, your airplane is trying to warn you that something is wrong. When the main breaker (I assume you mean the battery bus) trips, your airplane is screaming that something is wrong. That is one big breaker. Combined with the burning smell you have a serious warning that you could be at risk of an electrical fire in flight. There are not many airborne emergencies that are worse than an electrical fire. It can go from “sniff sniff- what’s that?” to really ugly in seconds.

Not trying to lecture. Just concerned for your safety. The Mooney POH doesn’t have much to say about resetting tripped CBs in flight but most airlines forbid it unless absolutely critical for the safety of flight. I would not fly your airplane again without determining the cause of the tripped CBs and ensuring that there was no damage to the electrical system. I have had the gear CB trip once in my airplane. I left it out, lowered the gear manually and landed. My AME found that my actuator was in need of an overhaul but that did not fully solve the problem. Further investigation revealed a bad cannon plug with corroded and burnt contacts. 

Good luck with the diagnosis.

 

I’m in general agreement, especially if there’s anything accompanying the popped cb (especially smoke smell), but most airplane manuals allow for one reset of a cb in flight in absence of other fire indications.  
 

In military airplanes I flew we always used the one reset rule, in the Meridian I fly at work, almost everything is electric and it allows for one reset as well.  The Mooney?  Well, they don’t really go into that in the ‘68 poh!

 I agree, there’s likely a reason the cb popped, so sometimes it’s worth looking into, but sometimes it just popped or the cb is getting old and warning you that it will eventually need replaced.

[squeaky.stow]

The consensus on resetting in flight has evolved a lot over the years. Back when many of our Mooneys were being built, the conventional wisdom was to push it back in and see what happens. That was certainly the general belief when I was in the military. I suspect that Mooney subscribed to that theory and didn’t feel it necessary to provide any further guidance.

Since those days there have been a few high profile tragedies that have resulted in both airlines and manufacturers rethinking their guidance. Air Canada had a tragic fire in a DC-9 in 1983 as a result of the crew resetting a tripped CB for a lavatory. 23 died.

Around that time policies began to change to restrict unlimited resets, but there was still a belief that it was OK to “troubleshoot” electrical problems in flight, even serious ones. Airlines and military both had checklists with complex procedures for dealing with electrical fires that involved shutting down entire busses and then gradually repowering one system at a time to try and isolate the problem. Swissair was doing something along those lines when they crashed into the bay of Fundy. 
 
After Swissair the industry went through a sea change. The policy for most airlines now is that if a CB trips, you leave it. If there are indications of electrical fire, you put the airplane on the ground. Now. (Current RCAF policy now is only for safety-critical systems and only once.) From a Mooney perspective you have to ask yourself what is a safety-critical, i.e. “is safety jeopardized if I don’t get this back?

I was responsible for some of those SOPs at my airline, but I wasn’t alone. Boeing and Airbus now provide similar guidance. Yes, there might be many benign reasons for a CB tripping in flight, and resetting may fix everything with no ill effects, but is it worth the risk? We have no way of knowing what caused the trip while we are in flight so resetting is essentially playing Russian Roulette with no idea how many bullets (if any) are in the gun.

[carusoam]

Old planes...

old grease... Turns to rocks...not very helpful...

old designs... 20:1 vs 40:1, puts extra load on the motor...

old pilot  ... not aware of the accidental interaction between the manual gear and the electric gear, a brass gear gets Fubar’d

Old England... Not sure who your Maintenance group is... but @Hyett6420 Andrew has some really good M20J landing gear system experience.  he took many pics and posted them around here...  it is possible Andrew May have some details to share... possibly who to take your Mooney too...
 

Old solution... Put plane up on jacks and operate the gear... testing each and every aspect of it... the gear has specific maintenance procedures to set it up properly...  expect having the procedures and tools will be important... and somebody that knows how to do it...

What gets old really fast... Mooneys with improper gear set-up... nothing like having a gear collapse... That is a very expensive experience to be avoided...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

 

[Ragsf15e]

22 minutes ago, squeaky.stow said:

The consensus on resetting in flight has evolved a lot over the years. Back when many of our Mooneys were being built, the conventional wisdom was to push it back in and see what happens. That was certainly the general belief when I was in the military. I suspect that Mooney subscribed to that theory and didn’t feel it necessary to provide any further guidance.

Since those days there have been a few high profile tragedies that have resulted in both airlines and manufacturers rethinking their guidance. Air Canada had a tragic fire in a DC-9 in 1983 as a result of the crew resetting a tripped CB for a lavatory. 23 died.

Around that time policies began to change to restrict unlimited resets, but there was still a belief that it was OK to “troubleshoot” electrical problems in flight, even serious ones. Airlines and military both had checklists with complex procedures for dealing with electrical fires that involved shutting down entire busses and then gradually repowering one system at a time to try and isolate the problem. Swissair was doing something along those lines when they crashed into the bay of Fundy. 
 
After Swissair the industry went through a sea change. The policy for most airlines now is that if a CB trips, you leave it. If there are indications of electrical fire, you put the airplane on the ground. Now. (Current RCAF policy now is only for safety-critical systems and only once.) From a Mooney perspective you have to ask yourself what is a safety-critical, i.e. “is safety jeopardized if I don’t get this back?

I was responsible for some of those SOPs at my airline, but I wasn’t alone. Boeing and Airbus now provide similar guidance. Yes, there might be many benign reasons for a CB tripping in flight, and resetting may fix everything with no ill effects, but is it worth the risk? We have no way of knowing what caused the trip while we are in flight so resetting is essentially playing Russian Roulette with no idea how many bullets (if any) are in the gun.

Fair enough.  As I said I’m in general agreement.  Maybe some manufacturers are still thinking about it?  The Meridian is only 5 years old and they still suggest a reset.  Your point about not needing to troubleshoot while airborne is solid though.  I definitely agree with that.

[mikebroady]

4 hours ago, Hyett6420 said:

Greetings, liver birds (the OP will get that if he's from liverpool.)  
 

thanks for the call Anthony.  I agree with most people on here when they say if you have to reset the cb more than once something is wrong.  The gear system on a mooney is VERY simple.  Designed using parts from a wellington bomber, the worm drive motor assembly, it is the equivalent of those old 1930s upper windows you used to get in libraries and dormitories, where you wound a handle at the bottom, this  turn a cog, which moved its way up a bar and closed the window.  Same on the mooney, the worm drive turns a cog, along a bar which rotates and puts the wheels up or down.  IF it is nit adjusted properly, then you can overload the motor very easily and CBs will pop.  
 

in ‘16 i spent the whole year searching in the UK for a place that REALLY understood mooneys and did not look like a 1960s car maintenance facility.  I did not find one, NOT ONE.  They all knew Cessnas, and Pipers and “thought” they knew Mooneys, but they didn't, and quite often were learning on your plane.  You would not take your Ferarri to a ford dealer now would you?  After a lot of searching I found Aeroskill mastenbroek in Seppe (EHSE) in Holland, a quick 1 hour mooney trip.  They are the ONLY mooney service centre in Europe.  Being Dutch, they call a spade a spade, not a digging implement.  Take your baby across there, let them look at it.  They have all the tools, jigs, etc needed to setup the gear just so and find any faults.  Tell them Andrew sent you.  Every person I have sent there has been happy. 
 

do a google search for “no back spring hyett6420 mooneyspace” and you will see the wormdrive assembly.  
 

Happy to dm and call on mobiles if easier.

 

Andrew

 

Hi Andrew, thanks for your post and I'll return to that in a moment.

I think I gave too much information in the initial post and frankly I was looking for any technical pointers before referring to the engineers, those that may have experienced a similar situation or have a more in-depth knowledge.

For those interested in commenting on my actions perhaps I can put your minds at rest.

When the main breaker tripped in 2012 I was downwind at Liverpool John Lennon when I noticed some smoke on the passenger side panel area and the main breaker had tripped. I declared an emergency, ATC stopped all traffic, deployed the fire tenders and I landed immediately with no further problem. I never attempted to reset the breaker. We had the panel apart and the engineers spent several hours looking for the fault. All they could find was a pen lodged behind the panel but with no evidence it was the culprit. I've flown a few hundred hours since with no further problems until Feb this year when the main breaker tripped shortly after take off following several touch and goes. Again, because it was the main breaker I made no attempt to reset it and landed immediately. When I reset it on the ground it gave no further problems. I had the engineers look for the problem on the 50hr inspection the next week but they could find no evidence of an issue. 

Intermittent problems like this are a nightmare, but I know from my automotive experience that all the information you can possibly gather helps to solve the issue in a reasoned and logical manner. I'm not saying these are definitely connected to the last incident when the landing gear breaker tripped, but two of the electrical operations are landing gear and flaps on both downwind and take off, so just maybe there is a connection.

Re the landing gear breaker trip on Thursday. We were after hours at the local airfield so the option of getting someone in the tower or on the ground to check the gear on a low pass didn't exist. The manual indicator showed the gear down but the light showed unsafe, so I had two choices. Carry on and land, but the gear may not be locked and I could suffer a collapse on landing with no emergency facilities, or divert. I decided to climb and try to assess the problem knowing we were right overhead the field and I had the manual gear option. Mindful that there was a slim chance we could end up with an electrical fire I asked my passenger to make ready with the fire extinguisher and in this event resolved to turn off the fuel, vents and masterswitch and get her on the ground post haste, either gear up or down. Resetting the breaker solved the issue thankfully and the gear and warning lights functioned properly through a couple of cycles.

I am comfortable with all my actions and don't think I would do any different if faced with the same set of circumstances. I'd like to keep the comments to technical advice if that's possible so hopefully this reply will put the others to bed.

Andrew. I'll check the worm drive link, thanks. Whilst I learned to fly at Liverpool and based WR there for a few years I live in Shropshire and have her in my hanger at Sleap now. I wasn't being disrespectful to my maintenance facility when I said I doubted a Mooney gear specialist existed in the UK and your comments bear this out. However, they have done a good job of maintaining her over the years so I will refer back to them in the first instance. They know the plane. If I don't feel confident I'll consider trying your recommendation. 

BTW, I thought Troyes Aviation were also a MSC, I've contacted them a couple of times for parts but on the whole find Lasar exceptionally helpful.

Regards,

Mike

[Andy95W]

6 hours ago, Hyett6420 said:

Greetings, liver birds (the OP will get that if he's from liverpool.)  

 

I thought the proper term was Scouse?

[carusoam]

An easy test for a shop’s skills... For this type of work... gear rigging and flight control rigging is somewhat a specialized skill... 

1) Setting up, or properly testing, the gear over-center forces require a couple of specific tools...

2) Do they have the tools?

3) Is the paint worn off them? Or are they dust covered From the last century...?

Like any control rigging exercise... tools and experience count.

For the most part... rigging doesn’t usually drift on its own...

Grease does turn to rocks on its own...

letting the smoke out of things, often leaves a mark.  How is your access from the top of the instrument panel..?  See what is leaning against the back of the gear switch...

Sometimes a new installation of something leaves small metal flakes / swarf fallen into something that isn’t well protected...
 

Anything new get installed lately?

Was the last flight more bumpy than usual flights?

 

PP thoughts about what could cause a CB to protect its motor.... and things that cause a CB to trip otherwise... not a mechanic...

Best regards,

-a-

[PT20J]

By "main" breaker, I assume you mean the ALT breaker. The other "main" possibility would be the BAT breaker, but if that trips you would not have power for the low voltage annunciator.

Generally, the alternator does not supply enough current to trip the ALT breaker. The purpose of the breaker is to protect against a short in the alternator or its wiring. There are some large wires attached to these breakers and they are in close quarters. The act of pulling out the circuit breaker panel and replacing it might have corrected the problem, but it wouldn't hurt to check the clearances. In my airplane, Mooney glued some plastic spacers between some of the adjacent breakers as insulation and the glue had deteriorated with age and the plastic spacers had moved out of position.

Your symptom of putting the gear down, having the gear breaker pop with the mechanical indicator showing down and the gear unsafe light on indicates a problem with the down limit switch circuit. The motor runs against the mechanical stop but does not shut off and stalls tripping the breaker. The gear is down, but the green gear down light will not illuminate because the down limit circuit is not working.

Skip

[mikebroady]

5 hours ago, Andy95W said:

I thought the proper term was Scouse?

Correct Andy,  but normally they are referred to as Scousers. Scouse is a meat and vegetable stew which I think came from the Nordic regions via sailors, became popular and gave way to the term Scousers for a Liverpudlian. Think it's also called lobby too. The Liverbirds are two statues on top of a building overlooking the River Mersey, and also a TV comedy series way back!

[mikebroady]

54 minutes ago, PT20J said:

By "main" breaker, I assume you mean the ALT breaker. The other "main" possibility would be the BAT breaker, but if that trips you would not have power for the low voltage annunciator.

Generally, the alternator does not supply enough current to trip the ALT breaker. The purpose of the breaker is to protect against a short in the alternator or its wiring. There are some large wires attached to these breakers and they are in close quarters. The act of pulling out the circuit breaker panel and replacing it might have corrected the problem, but it wouldn't hurt to check the clearances. In my airplane, Mooney glued some plastic spacers between some of the adjacent breakers as insulation and the glue had deteriorated with age and the plastic spacers had moved out of position.

Your symptom of putting the gear down, having the gear breaker pop with the mechanical indicator showing down and the gear unsafe light on indicates a problem with the down limit switch circuit. The motor runs against the mechanical stop but does not shut off and stalls tripping the breaker. The gear is down, but the green gear down light will not illuminate because the down limit circuit is not working.

Skip

Good post Skip. Yes, It was the Alt breaker and I can see sense in all you say. Thanks.

[mikebroady]

4 hours ago, carusoam said:

An easy test for a shop’s skills... For this type of work... gear rigging and flight control rigging is somewhat a specialized skill... 

1) Setting up, or properly testing, the gear over-center forces require a couple of specific tools...

2) Do they have the tools?

3) Is the paint worn off them? Or are they dust covered From the last century...?

Like any control rigging exercise... tools and experience count.

For the most part... rigging doesn’t usually drift on its own...

Grease does turn to rocks on its own...

letting the smoke out of things, often leaves a mark.  How is your access from the top of the instrument panel..?  See what is leaning against the back of the gear switch...

Sometimes a new installation of something leaves small metal flakes / swarf fallen into something that isn’t well protected...
 

Anything new get installed lately?

Was the last flight more bumpy than usual flights?

 

PP thoughts about what could cause a CB to protect its motor.... and things that cause a CB to trip otherwise... not a mechanic...

Best regards,

-a-

Nothing new but I did look to see if the Autopilot would slide out easily over another issue before the last flight. Maybe it moved or pulled some wiring or something behind the panel in the process. Worth a look from underneath I reckon. Thanks.

[carusoam]

Summary of the things that stand out in this conversation...

1) limit switch doesn’t seem to be showing the position of the gear properly...

2) That seems a bit odd, since the gear motor may be using the sensor to turn the motor off...

3) Is it possible that the gear went down and hit the stops and keep trying to drive the gear motor? That should trip a specific landing gear CB..?

4) You were doing TnGs In a Mooney? While ROP? Or LOP? T/O flaps used? Full flaps while landing? and other fun discussion had here Monthly...   
 

Are you making any headway on this?

PP thoughts only, not a mechanic...

Best regards,

-a-

[Yetti]

Grease the gear all 4000 grease zerts

Replace the breaker

Grease and inspected the gear actuator

Operate on jacks.   Should also do a manual gear extension.

In the air if you are having issues with the gear and it is down.   Leave it down.  Finish the extension with the manual handle.

Unless it is bent or been jacked with the gear preload should be fine and don't start playing with the limits unless there is a good reason.