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BaldEagle

Gear retract issue today - M20J

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Hi all,

Departing a high density altitude this morning, 85KIAS bring the gear up and the Gear Down and Gear Unsafe annunciator lights illuminated with an audible alarm sounding.  Recycled the gear, and on the second attempt the gear retracted and we continued to our destination without incident.  Anyway, I mention it here because I must have north of 1,000 hours retract time in various singles and twins without a single issue until today.  I only have about 12 hours on my "new" '78 J, and was under the impression that the gear systems on these flying machines are generally very robust.  Anything I should be concerned about?  Take it to the shop, or something I can investigate initially myself?

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I would lubricate your limit switches with contact cleaner or TriFlow. Do the squat switch while you are at it.

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Better swing it on the jack to test it out. 

You don't want to take any chances with a possible gear problem. 

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The mechanics of the gear systems are pretty robust.  The electronic sensors, and indicators, arguably not so much.  Indeed, for whatever reason, people have posted a rash of gear warning problems lately.

To understand your problem, you really need the electrical schematics for your particular make and model, located in the Service Manual.  Note that different Mooneys have different gear warning systems.  Among the electric gear models, the systems are similar, but not always exactly the same.  If you or your mechanic don't have the schematics, you're just guessing.  Same about advice given here - the more directly said advice references the schematics, the more likely it is to be right.

I have a set of schematics for M20J S/N 24-001 through 24-0237.  Based on that, I'm going to guess your problem is either a malfunctioning/mis-adjusted squat switch, or landing gear doughnuts that didn't expand enough after liftoff to trigger the squat switch.  That seems to fit the conditions you described.  The logic of the system according to the schematics is that if the gear selector is moved to the up position when the squat switch "thinks" there is still weight on the wheels, the gear horn will sound, and the gear unsafe light will illuminate.  Since the gear is still actually in the down and locked position, the gear down light will also be illuminated.  Note that while it might be a good idea to clean the limit switches in the belly, they likely have nothing to do with this problem.

Suggest the first thing you do is examine the condition of your main landing gear doughnuts.  Does the gap measured at the retainer collar exceed the limits in the maintenance manual?  You measure this with the airplane on the ground and full fuel in the tanks.  No disassembly is required, so you can measure it yourself - no A&P required.  When were the doughnuts last replaced?  If it's been a long time since the last replacement and/or the retainer collar measurement is beyond limits, it's likely the doughnuts are slow to expand on liftoff, and therefore aren't triggering the squat switch.  In this case, the gear can fail to retract immediately after liftoff, but will eventually retract if you simply wait a while for the doughnuts to expand.  Sounds like what might have happened to you.

If you're sure the doughnuts are in good shape, you'll need to get with a mechanic and put the airplane on jacks to test/adjust the squat switch.  There is just too much that can go wrong fiddling around with the squat switch while the airplane is on the ground.

 

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A 78’ J will have an Airspeed safety switch. I had that same problem this time last year. Next chance you get climb out as slow as you feel comfortable 85mph or so. If the gear doesn’t go up, pitch the nose over to 90 or faster and see if the gear goes up. If so the bad news is $1,400 for the switch.


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Not sure if my ‘75F is the same as your J.  My gear symptoms were EXACTLY like yours. Turns out my doughnuts were old, really old!!!!!   Look at the numbers stamped on them to get a date. I replaced all my gear doughnuts and solved my problem.  

Jason

 

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Just to follow up on this thread, my J does has the airspeed safety switch as opposed to a squat switch.  After digesting the POH, I took the airplane up and the gear retracted as normal.  I think the issue was with the pilot: hot day, high density altitude, obstacles at the departure end of the runway and bringing the gear up earlier than I normally would to clean up the airframe; airspeed was likely below what the airspeed safety switch is set to (no mention of what that number is in the POH).

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46 minutes ago, BaldEagle said:

Just to follow up on this thread, my J does has the airspeed safety switch as opposed to a squat switch.  After digesting the POH, I took the airplane up and the gear retracted as normal.  I think the issue was with the pilot: hot day, high density altitude, obstacles at the departure end of the runway and bringing the gear up earlier than I normally would to clean up the airframe; airspeed was likely below what the airspeed safety switch is set to (no mention of what that number is in the POH).

Airspeed safety switch speed is in the Maintenance manual, IIRC its in the 60-67 kts range. If you have jacks, you can test it out in your hangar to verify if its in spec per your Maintenance manual cause I'd bet you were probably over the spec'd speed since its pretty low. But also next to your gear switch in the cabin should be a red switch that illuminate when the gear switch is up but the air speed safety switch is preventing the gear from rising along with the horn activating. You only need to push the illuminated red switch to bypass the airspeed safety switch and raise the gear. Not absolutely sure which year the bypass switch started but I thought with the early J's and its been retrofitted to many F's and can be added if you don't have one yet. That's the correct action while climbing out of a high density airport whenever necessary.

Were are you at KSEE? I am Sky Harbor D-7 near Circle Air. Come say hello some time whenever near by.

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I'm currently tied-down at El Cajon Flying Services, south of SAA.  Will go shopping for a hangar after my first annual.  By the way, we did have an email exchange a few months ago for Mooney transition training: I'm getting back into aviation after a 13-year hiatus and was expecting some 10 hour transition training requirement from the insurance company, but in the end they just wanted a check-out so I did that with the ferry pilot, who was also a CFI (in case you're wondering why you never heard back from me!).

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Airspeed safety switch speed is in the Maintenance manual, IIRC its in the 60-67 kts range. If you have jacks, you can test it out in your hangar to verify if its in spec per your Maintenance manual cause I'd bet you were probably over the spec'd speed since its pretty low. But also next to your gear switch in the cabin should be a red switch that illuminate when the gear switch is up but the air speed safety switch is preventing the gear from rising along with the horn activating. You only need to push the illuminated red switch to bypass the airspeed safety switch and raise the gear. Not absolutely sure which year the bypass switch started but I thought with the early J's and its been retrofitted to many F's and can be added if you don't have one yet. That's the correct action while climbing out of a high density airport whenever necessary.
Were are you at KSEE? I am Sky Harbor D-7 near Circle Air. Come say hello some time whenever near by.

I’ve read it requires an a&p to do a gear swing. Is that not true?


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1 hour ago, xcrmckenna said:


I’ve read it requires an a&p to do a gear swing. Is that not true?


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Technically anything not listed under Preventative Maintenance requires A&P supervision - so I would think yes. And some would also extend that reasoning to say that in a retractable gear Mooney, a pilot really isn't allowed to change a tire since when changing a tire on a retractable AC the FAA guidance under 43.13b requires us to make multiple gear swings to ensure the new tire doesn't catch anywhere and the gear doors  are still properly rigged since these additional activities fall out of the scope of PM on retractable aircraft.

Until it happened to me, I used to buy in to the argument of some that if you don't change the tire brand/model you should be safe to skip the gear swing checks. But then I put on a new FCIII tire which did bind when the old worn one did not. This had me stumped till I traced the issue to a new shock link tower installed when the tire had about half it's tread. It was off dimensionally just enough to cause the problem. Replacing the pretty new shock link with yet another new one solved my problem. That was one time I was glad I didn't skip the gear checks or I would have had problems soon after. 

Personally, I've always suggested the same advice that I am required to follow as an A&P, if you've never done the task before, always seek supervision from an A&P that has the first time you take it on to make sure you learn how to do it properly; even its only changing the oil or a spark plug.  There is the legal aspect and then there is safety and protecting those that fly with you.

Edited by kortopates
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19 hours ago, kortopates said:

Airspeed safety switch speed is in the Maintenance manual, IIRC its in the 60-67 kts range.

It's actually listed in the POH as well, in section VII.  Mine says "65 KIAS, +7 -4."  Why they didn't just say 61-72 KIAS is beyond me :)

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