1998 Encore recurring issue: landing gear won't retract

[bcbender10]

Hello Mooney world,

General broadcast for insight into a recurring landing gear retraction issue. Yesterday the landing gear failed to retract for the 3rd time. My A&P (Andres Gonzales at Bill's Air Center at SMO) temporarily fixed the issue twice before. However, he has suggested I take the plane elsewhere for a repair. He reports the issue is very challenging to troubleshoot.

I purchased 43PG on Aug 30. On my initial checkout with Paul Kortopates, the gear failed to retract on the 4th take off at SMO. Andres troubleshot and identified the "Up" relay to the solenoid as the issue. Both the "up" and "down" relays were replaced. Andres reported "about 50" successful gear cycles on jacks in the shop.  The plane was returned to service.

I completed my check out with Paul, putting about 20 additional cycles on the gear with no issues. The day after my sign off, I flew to Glendale, AZ about 1.6 hours at 15,500ft. On departure from GEU, gear did not retract. I elected to fly back to SMO (POH EP allows continuation of flight, if desired. I wanted Andres to troubleshoot and conditions were day VFR). 

Andres identified a loose electrical connection at the wire into the solenoid. He reported replacing washers with lock washers (and stated the leads were tight in the inspection in the first repair). Plane was returned to service. 

On Friday evening I put 5 cycles on the landing gear. Saturday morning the gear retracted fine (6 total cycles). On Saturday I flew to MMH (about 1.6 hours at 14,500 ft). Gear did not retract on departure from MMH. Very dangerous situation with density altitude at 9,500 ft. I landed at MMH to see if a landing cycle would reset/correct a limit switch or relay. Gear did not retract on next take off. Plane is currently at SMO.

Correlation is not cause, but are the >1 hour flights at higher altitudes related? Extremely concerning, costly, and inconvenient for this issue to appear the last 2x on long x-country trips.

Indications are always the same: Gear down light is lit the entire time; "Gear Unsafe" light never illuminates; mechanical indication is "Green/gear down".

My plane is going into annual and to fix a number of squawks at LASAR on November 20th. I'm concerned that even if they fix the issue, it will reappear after 5-20 cycles unless a root cause is identified and addresses.

Not sure what to check/investigate/do now. My A&P is out of ideas.

Edited October 27, 2019 by bcbender10
grammar edits for clarity

[carusoam]

Getting to a Mooney expert seems like the right way to go...

let’s invite Paul to the conversation... @kortopateshe May have additional observations to include...

There isn’t anything better than Lasar...

They will have all the proper electrical and mechanical drawings... and people that really know what they are doing... tons of Mooney specific detailed experience...

(being careful to not accidentally say anything negative towards your experience, mechanics, and flight instructors....)

Each part of the system can be tested for its operation... it is a simple collection of parts...

• switch
• motor
• gearbox
• sensors up limit, down limit
• relays... electrical devices that often include the switches...
• wires
• lubrication
• rigging

Any idea what fails, when it fails, any binding or strange noises, any bumps, normal or abnormal...?

There have been situations where Landing gear push / pull rods have bound until they broke...

Has the landing gear been set-up /rigged properly?

If the gear hasn’t had its rigging checked... this would be a great place to start...

Landing gear failures aren’t normal...

Some are simple... squat switch, temperature dependence, and old donuts...

Some are more complex... out of rig, tube twisting, and failure...

on another ship, (non-Mooney) I have experienced a binding of the gear system... a bolt was simply placed in position in reverse to what was requires... it saw extra strain while going over center... finally breaking a rod end bearing... for a gear door... phewww... that was close... 

Soooo...

How are you handling the gear failure when it happens?

• pushing the gear bypass button... simple
• hand cranking the gear down... great, once...
• recycling the switch, while praying, until it works... not recommended..

PP thoughts only, not a mechanic...

Best regards,

-a-

[bcbender10]

Thanks for your reply. I, too, suspect root cause is a mechanical issue. Unknown on landing gear rigging. No issues on pre-buy and the landing gear cycled just fine on the pre-buy flight.

When the landing gear doesn't retract, I follow the EP in the POH to the letter. (I'm a former navy nuke power officer. I'm good at following procedures!). The EP includes (from memory fo this post reply) pulling the gear actuator circuit breaker and moving the switch to the "down" position (from "up"), reseting the actuator circuit breaking and trying again. then pushing gear bypass button. 

This is a failure to retract issue, not a gear extension issue. There is no option/capability to hand-crank the gear up. 

I'm not the praying and random action type, especially when it comes to unexpected conditions covered in EPs.

Seems like I'll be enjoying Arrow speeds at high fuel flows for a ferry flight to LASAR from SMO!

[carusoam]

Great details, bcb!

there are a couple of initial conditions that probably need to be aligned for the system to move...

The maintenance manual may cover things like switch positions and logic... squat switches are known to mis behave.

The flap systems are similar in complexity... relays and switches... and logic chart...

 

Of course... the gear switch might be misbehaving or one of the wires it is attached to...  

Check if you have an airspeed switch or squat switch.

 

Some common old airplane challenges are fixed with an electronics cleaner...

Mooney squat switches improve when their gear donuts get changed out...

PP thoughts only, not a mechanic...

Best regards,

-a-

 

 

[j3gq]

Let me respond with some common wisdom drawn from many years in shuttle operations. 
- micro-electronic circuits never fail
- power electronics fail ... sometimes (after stress through high E and B fields)
- electric devices, switches, cables etc. fail (more often when significant power or moving parts are involved)
- mechanisms fail more often than electrics than electronics
- mechanical devices fail the most often.
This assumes quality design, proper QA and PA, no corrosion issues, no radiation. Normal aging, thermal cycle and vibrations are included in the statistics.

This may not solve your problem. But it gives you some idea where to look first. My best shot (and I really do not have enough information for more than that !) :

Your A&P would have found the obvious mechanical problems, but I am sure (from your account) he did not open and check the gear actuator. This would be my first suspect. How old is it ? when has it been serviced and by whom ? SIM 52 or 92 done ? is it a Plessey or Eaton. Be careful and don't trust this can only happen on gear retract. The next time it can block gear down and block your emergency gear down mechanism too,

If you need better advice ... I'd suggest you contact Kerry (www.knr-inc.com) before you spend any money on it. Be prepared to answer very detailed questions. Good luck

 

[carusoam]

Nice looking site...

https://www.knr-inc.com

J3, how did you come across this site?

Their first article is interesting... Jan 2019.

https://www.knr-inc.com/shoptalk-articles/25-shoptalk/93-201901-electric-gear-safety-system

Best regards,

-a-

[j3gq]

I think I found him through MAPA many years ago. He wrote for them issue after issue, subject after subject. If you thumb through the older shop-talk articles you'll see there is no stone left un-turned. Over the years his knowledge online and offline saved me thousands.

[Ragsf15e]

2 hours ago, bcbender10 said:

Thanks for your reply. I, too, suspect root cause is a mechanical issue. Unknown on landing gear rigging. No issues on pre-buy and the landing gear cycled just fine on the pre-buy flight.

When the landing gear doesn't retract, I follow the EP in the POH to the letter. (I'm a former navy nuke power officer. I'm good at following procedures!). The EP includes (from memory fo this post reply) pulling the gear actuator circuit breaker and moving the switch to the "down" position (from "up"), reseting the actuator circuit breaking and trying again. then pushing gear bypass button. 

This is a failure to retract issue, not a gear extension issue. There is no option/capability to hand-crank the gear up. 

I'm not the praying and random action type, especially when it comes to unexpected conditions covered in EPs.

Seems like I'll be enjoying Arrow speeds at high fuel flows for a ferry flight to LASAR from SMO!

What type of “retraction prevention” device is on your airplane?  Common Mooney ones are an airspeed switch (brass, big, pitot lines connected) behind your asi in the panel or squat switch in the gear wells?  

Both can fail.  It seems easier for the squat switch to stick or be slightly out of alignment and prevent gear retraction.

 I might figure out which you have for yourself and then have your current mechanic have a look if it’s a squat switch.  Maybe a simple adjustment or shot of triflow.  Its worth the effort until she’s up at lasar for next month.

[chriscalandro]

Your current problem sounds unrelated to your previous problem. I wouldn’t try to witch hunt for what is a root cause of ALL the issues, just the one at hand. 
 

the first one sounds like it was just the solenoids. The second was an issue introduced from installation of the solenoids. 
 

if this isn’t the solenoids it’s something completely different, bad luck, and probably completely unrelated. 

[buddy]

Have you tried pushing the RED bypass button with the gear handle in the up position? Push and hold till the gear fully retracts. Won’t solve your problem but at least you won’t be flying around with your gear down. If the gear does retract when pushing the bypass it may be an airspeed switch.

[squeaky.stow]

Not sure how much changed between 1986 and 1998 M20Ks but on mine there are several cannon plugs in various locations between the gear handle and the gear motor. I had an intermittent gear problem that was eventually found to be one bad pin in one of these plugs, but it took a lot of gear cycles on jacks while playing around with the wiring and cannon plugs to figure it out. Mine was not exclusively a retraction issue; it would fail during extension as well, and the cannon plug that was bad was in the belly quite close to the gear motor so it was one of the easier ones to access. If you know for sure that it only occurs during retraction that may help to eliminate some of the cannon plugs. Wiring diagram should help to narrow that down. Nothing more frustrating than an intermittent fault!

Good luck.

[bcbender10]

3 hours ago, buddy said:

Have you tried pushing the RED bypass button with the gear handle in the up position? Push and hold till the gear fully retracts. Won’t solve your problem but at least you won’t be flying around with your gear down. If the gear does retract when pushing the bypass it may be an airspeed switch.

Yes. Each incident, per the EP in the POH.

[bcbender10]

7 minutes ago, squeaky.stow said:

Not sure how much changed between 1986 and 1998 M20Ks but on mine there are several cannon plugs in various locations between the gear handle and the gear motor. I had an intermittent gear problem that was eventually found to be one bad pin in one of these plugs, but it took a lot of gear cycles on jacks while playing around with the wiring and cannon plugs to figure it out. Mine was not exclusively a retraction issue; it would fail during extension as well, and the cannon plug that was bad was in the belly quite close to the gear motor so it was one of the easier ones to access. If you know for sure that it only occurs during retraction that may help to eliminate some of the cannon plugs. Wiring diagram should help to narrow that down. Nothing more frustrating than an intermittent fault!

Good luck.

What's a cannon plug?.... searching Google. Thanks for the tip!

[bcbender10]

4 hours ago, Ragsf15e said:

What type of “retraction prevention” device is on your airplane?  Common Mooney ones are an airspeed switch (brass, big, pitot lines connected) behind your asi in the panel or squat switch in the gear wells?  

Both can fail.  It seems easier for the squat switch to stick or be slightly out of alignment and prevent gear retraction.

 I might figure out which you have for yourself and then have your current mechanic have a look if it’s a squat switch.  Maybe a simple adjustment or shot of triflow.  Its worth the effort until she’s up at lasar for next month.

thanks for the tip!

[carusoam]

One extra detail... that may possibly help....

in 94’ my Mooney was built using an airspeed switch in its gear system...

Expect most Mooneys built after that to follow along...

Best regards,

-a-

[Mark89114]

41 minutes ago, squeaky.stow said:

Not sure how much changed between 1986 and 1998 M20Ks but on mine there are several cannon plugs in various locations between the gear handle and the gear motor. I had an intermittent gear problem that was eventually found to be one bad pin in one of these plugs, but it took a lot of gear cycles on jacks while playing around with the wiring and cannon plugs to figure it out. Mine was not exclusively a retraction issue; it would fail during extension as well, and the cannon plug that was bad was in the belly quite close to the gear motor so it was one of the easier ones to access. If you know for sure that it only occurs during retraction that may help to eliminate some of the cannon plugs. Wiring diagram should help to narrow that down. Nothing more frustrating than an intermittent fault!

Good luck.

This was the issue I had, canon plug making poor contact.  On the Ovation, there are 3 from the CB panel down to the electrical parts in belly.  One behind the CB, which would have been a nightmare to get at, the second on the pilots side well and the third in the belly.  After hours of troubleshooting, my mechanic isn’t brilliant on electrical (another story), we traced it to the canon plugs in lower sidewall.  The power pin, which is always hot was intermittent.  It is conceivable that one of the two pins, one for up logic, the other for down have failed.  

[kortopates]

Wow, sorry to hear the problem returned soon after we last flew without issue. It has to be an electrical issue and more likely to be isolated to the circuits used for retraction instead of extension. Unfortunately the Maintenance manual isn't that helpful given the symptoms, so one really needs to pull out the schematic for your serial number and trace through the schematic for when the retraction circuit is energized or with the gear up switch in position starting with the airspeed pressure switch and work forward from there. But the time to do it is right after the gear fails to retract. But given the solendoids were just replaced, unless one has failed (infant mortality), one of the big suspects is the airspeed pressure switch. But the big data point against this is that we never saw the red bypass light illuminate nor did pressing the bypass button enable the gear retraction circuit to energize (at least not when we flew together) suggesting something downstream is at fault. But one really needs to look at the schematic in detail to trace the circuit to be certain - hopefully when it still won't retract. If all of sudden it works fine on jacks its going to be tough one to figure out but sometimes wiggling wires and connectors reveals a bad connection. 

Given the circumstances I'd probably want to get it up to LASAR sooner than later. But given the distance required to fly with the gear down, it makes trying out the other nearby MSC, Foothills at Upland, very appealing since they should also be very familiar with the gear electrics as well. Hope you get resolution soon!

Edited October 28, 2019 by kortopates

[ArtVandelay]

This was the issue I had, canon plug making poor contact.  On the Ovation, there are 3 from the CB panel down to the electrical parts in belly.  One behind the CB, which would have been a nightmare to get at, the second on the pilots side well and the third in the belly.  After hours of troubleshooting, my mechanic isn’t brilliant on electrical (another story), we traced it to the canon plugs in lower sidewall.  The power pin, which is always hot was intermittent.  It is conceivable that one of the two pins, one for up logic, the other for down have failed.  

Are canon plugs shown in the wiring diagrams, pretty sure they are for the J. If yes, I would get the service manual.

 

 

Tom

[kortopates]

Everything is in the schematic including the location of where it is. Here is a picture of the gear connector that's at the pilots sidewall - just have to pull the pilot seat and raise the carpeting to see it. Actually easily accessed. The picture shows one of the male connectors pushed back out to see them.

(also FWIW, its not legal to do "maintenance" without the service manual - its required but of course not always followed)

Edited October 28, 2019 by kortopates

[bcbender10]

12 hours ago, kortopates said:

Wow, sorry to hear the problem returned soon after we last flew without issue. It has to be an electrical issue and more likely to be isolated to the circuits used for retraction instead of extension. Unfortunately the Maintenance manual isn't that helpful given the symptoms, so one really needs to pull out the schematic for your serial number and trace through the schematic for when the retraction circuit is energized or with the gear up switch in position starting with the airspeed pressure switch and work forward from there. But the time to do it is right after the gear fails to retract. But given the solendoids were just replaced, unless one has failed (infant mortality), one of the big suspects is the airspeed pressure switch. But the big data point against this is that we never saw the red bypass light illuminate nor did pressing the bypass button enable the gear retraction circuit to energize (at least not when we flew together) suggesting something downstream is at fault. But one really needs to look at the schematic in detail to trace the circuit to be certain - hopefully when it still won't retract. If all of sudden it works fine on jacks its going to be tough one to figure out but sometimes wiggling wires and connectors reveals a bad connection. 

Given the circumstances I'd probably want to get it up to LASAR sooner than later. But given the distance required to fly with the gear down, it makes trying out the other nearby MSC, Foothills at Upland, very appealing since they should also be very familiar with the gear electrics as well. Hope you get resolution soon!

Thanks, Paul! I'll call Crown (or Coast now?)) Air in SD and Foothills today to check on availability. I'm not excited either about flying gear down to LASAR. Unfortunately, 1O2 runway is closed now for resurfacing. Anticipated re-opening is November 20th, so I can't fly the plane up any earlier. 

Very much appreciate your wiggling wires and connectors comment. I suspect vibration may be part of the cause (per 2nd fix - loose electrical wire connection to solenoid), and there's no vibration when on the jacks. I don't think it's the airspeed pressure switch. I've pressed the button each time (times 2 and 3, you did on the first time), with no response.

Thanks for your input that this must be an electrical issue.

[PT20J]

Since you can’t move it to someplace that can work on it, it might be worthwhile to do some further investigation if you are able. From the description, it is almost certainly electrical and probably not the airspeed switch. If you don’t have the Service Manual and schematics, call Mooney and ask for the pdf files. If you trace out the wiring on the schematic, you will see that it is pretty simple electrically - some microswitches, relays, switches and connectors. You can check all the connections and components individually. Don’t just wiggle them though. Part the connectors and check the conditions of crimps and pins. Some report good success applying Stabilant 22 to the contacts before reassembly. If you can borrow jacks, you can test the gear as you go along. Intermittent problems are challenging. Unless they see something obvious or reproducible, LASAR will just go through this same process. I’d also call a few MSCs and ask for ideas. Don Maxwell, Mark Rouch at Top Gun as well as LASAR have all been generous helping troubleshoot. Kerry McIntyre at KNR has also been helpful. These folks may be able to point you to the most likely problem component based on their experience.

Good luck.

Skip

[larryb]

I have a 1997 Encore. During my first post-purchase annual at my home MSC they found that the gear did not retract when on jacks. Now, I had had 0 problems in flight, but.... When the mechanic tapped one of the gear limit switches the gear retracted. So they replaced the limit switch. In your case it could very well be one of the gear limit switches. Expensive little buggers, not cheap like the flap limit switches.

 

Fast forward, I'm flying on the opposite coast 30 hours later and upon gear retraction the gear relay CB pops. Can't be reset. But if I put the gear switch in the Down position, I can reset the CB and the gear operates normally. To make a long story short, there is a bracket in the gear system that is very very close to the screw terminals on the up limit switch. In my case, they made contact and created a short that popped the breaker. So if you do have the limit switches replaced, make sure to visually inspect the screw terminal clearances with the gear both up and down.

 

Larry

[ilovecornfields]

Have you called Top Gun in Stockton? Seems like they might be able to help out. 

[MB65E]

Was just going to mention stable22.

Also, deoxit Gold is a great spray that helps with connections. 
How was your tech retracting the gear on jacks?
The gear should not retract unless the airspeed switch is bypassed or airspeed was applied. If he is bypassing the switch, it’s probably a bad airspeed switch. 
-Matt

[chriscalandro]

Anybody that can read an electrical drawing and has certification to fix it should be able to sort it out without much issue. 
 

it seems crazy to me to fly a distance to a MSC with something disabled. It’s electrical. Not anything the Mooney gods would have better experience with vs anyone familiar with basic electronics. Don’t fly it if you don’t have to. You’re assuming the issue doesn’t effect extension. Find someplace local or have someone come to you. 
 

everything needed is in the manuals. Do what you want but you don’t need a Mooney service center to fix this. I suspect this time it will be a limit or squat switch.Trouble shooting should be pretty straight forward while on jacks. 

Edited October 28, 2019 by chriscalandro