M20J - Gear not Retracting

[WheelPantsOff]

Good evening all,

My M20J started to act up on me where on the first retraction of the day the landing gear will not retract using the normal gear up sequence.  I use the gear bypass button to get it to retract and then on subsequent retractions that day, there's no problem.  I have no evidence in the logbooks that the airspeed safety switch was ever replaced.  This is a 24-14xx S/N range airplane and doesn't have the squat switch.  Other than looking at it physically to make sure nothing is obviously physically wrong looking or the connections have come loose, are there any basic tests I can do to start troubleshooting for my tech?

I had a .411/.413 check performed in March and I assume they didn't goose the air during the test, but it's also too long ago for me to point to that as a contributing factor.

Thanks in advance

[Ragsf15e]

32 minutes ago, WheelPantsOff said:

Good evening all,

My M20J started to act up on me where on the first retraction of the day the landing gear will not retract using the normal gear up sequence.  I use the gear bypass button to get it to retract and then on subsequent retractions that day, there's no problem.  I have no evidence in the logbooks that the airspeed safety switch was ever replaced.  This is a 24-14xx S/N range airplane and doesn't have the squat switch.  Other than looking at it physically to make sure nothing is obviously physically wrong looking or the connections have come loose, are there any basic tests I can do to start troubleshooting for my tech?

I had a .411/.413 check performed in March and I assume they didn't goose the air during the test, but it's also too long ago for me to point to that as a contributing factor.

Thanks in advance

@PT20J is the expert on the wiring diagram.  The other thing that can keep them down is the up limit switch.  I think the bypass only bypasses the airspeed switch though, so if that fixed it, maybe there’s your answer?  There is a second circuit available on the airspeed switches, so you may be able to switch your connection and still get it to work.

[EricJ]

The bypass is mostly just so that you can cycle the gear on the ground during a routine gear swing or other maintenance, but does also let you bypass a faulty airspeed switch.   It sounds like maybe the airspeed switch is just a little slow or sticky or something.

 

[1980Mooney]

2 hours ago, WheelPantsOff said:

Good evening all,

My M20J started to act up on me where on the first retraction of the day the landing gear will not retract using the normal gear up sequence.  I use the gear bypass button to get it to retract and then on subsequent retractions that day, there's no problem.  I have no evidence in the logbooks that the airspeed safety switch was ever replaced.  This is a 24-14xx S/N range airplane and doesn't have the squat switch.  Other than looking at it physically to make sure nothing is obviously physically wrong looking or the connections have come loose, are there any basic tests I can do to start troubleshooting for my tech?

I had a .411/.413 check performed in March and I assume they didn't goose the air during the test, but it's also too long ago for me to point to that as a contributing factor.

Thanks in advance

It is possible to repair in some cases. It could be the diaphragm or micro switches. Or calibration.   Read below.  Otherwise you need a new one for a couple $ thousand.  Lasar claims to sell for $900 but not clear if they have any —  says “call for availability” and “call to special order”…

https://lasar.com/switches/airspeed-safety-switch-656-3-880013-507
 

[WheelPantsOff]

Thanks, guys.  I had a couple of people claim that they can be 'cleaned' but they weren't clear on what you were actually cleaning, and from what I understand in the part, it's a bellows with two lines connected and electrical connections.  I don't know what you could possibly be cleaning.  If I were to get the airplane on jacks, and manually push air through the airspeed indicator to test wheat airspeed the gear is retracting, do you know what direction the screwdriver turn raises/lowers the airspeed threshold?

[Ragsf15e]

55 minutes ago, WheelPantsOff said:

Thanks, guys.  I had a couple of people claim that they can be 'cleaned' but they weren't clear on what you were actually cleaning, and from what I understand in the part, it's a bellows with two lines connected and electrical connections.  I don't know what you could possibly be cleaning.  If I were to get the airplane on jacks, and manually push air through the airspeed indicator to test wheat airspeed the gear is retracting, do you know what direction the screwdriver turn raises/lowers the airspeed threshold?

There’s a “shoptalk” or mapa article describing this with pictures. I’ll Look around with some google-fu and i think itll help.

[Ragsf15e]

https://knr-inc.com/shoptalk-articles.html?view=article&id=93&catid=25
 

@WheelPantsOff, try this.

[WheelPantsOff]

19 minutes ago, Ragsf15e said:

https://knr-inc.com/shoptalk-articles.html?view=article&id=93&catid=25
 

@WheelPantsOff, try this.

Beautiful.  Thank you!  I'd like to see if it's adjusted properly.  I'm in the AMM on page 32-60-00-28 and see where it discusses adjustment and finding out where the trigger is set to, but it doesn't explain how to test that with a multimeter.  Any insight would be appreciated before I start taking things apart.

Edited August 3 by WheelPantsOff

[RangerM20]

What you have to do is get a LONG piece of tubing to cover the pitot tube, then reduce it down to where you can fit a length of surgical tubing on the end through the storm window.  Put the aircraft on jacks, switch power on, select the gear to UP, then roll the tubing until the gear comes up and note the reading.  If it never comes up, then remove the glareshield, and check the wires and connections.  The Beechcraft Duchess uses this same system, and perhaps the same sensor.

[1980Mooney]

1 hour ago, WheelPantsOff said:

Beautiful.  Thank you!  I'd like to see if it's adjusted properly.  I'm in the AMM on page 32-60-00-28 and see where it discusses adjustment and finding out where the trigger is set to, but it doesn't explain how to test that with a multimeter.  Any insight would be appreciated before I start taking things apart.

It’s just continuity - open or closed. Ohms or continuity on your meter

[Larry]

DO NOT blow directly in the pitot tube.  Someone passing by might get the wrong idea how much you love your Mooney!

 

[Ragsf15e]

2 hours ago, WheelPantsOff said:

Beautiful.  Thank you!  I'd like to see if it's adjusted properly.  I'm in the AMM on page 32-60-00-28 and see where it discusses adjustment and finding out where the trigger is set to, but it doesn't explain how to test that with a multimeter.  Any insight would be appreciated before I start taking things apart.

The easiest way is with it up on jacks and an air system (pitot/static tester).  Put the gear switch up and then slowly increase airspeed until the gear goes up.

[Fly Boomer]

3 hours ago, WheelPantsOff said:

If I were to get the airplane on jacks, and manually push air ...

This might be something to check before tearing into the panel.  From the KNR article

"Any obstruction or contaminants such as oil or water in the pitot or vent (static) will affect the operation of the diaphragm"

[WheelPantsOff]

6 hours ago, RangerM20 said:

What you have to do is get a LONG piece of tubing to cover the pitot tube, then reduce it down to where you can fit a length of surgical tubing on the end through the storm window.  Put the aircraft on jacks, switch power on, select the gear to UP, then roll the tubing until the gear comes up and note the reading.  If it never comes up, then remove the glareshield, and check the wires and connections.  The Beechcraft Duchess uses this same system, and perhaps the same sensor.

 

6 hours ago, 1980Mooney said:

It’s just continuity - open or closed. Ohms or continuity on your meter

Just did this.  Gear started to retract at about 95 KIAS.  Is the airspeed safety switch adjustable with the flatblade screwdriver protrusion (I don't know how else to explain it) facing towards the forward of the aircraft?

[PT20J]

21 minutes ago, WheelPantsOff said:

Just did this.  Gear started to retract at about 95 KIAS.  Is the airspeed safety switch adjustable with the flatblade screwdriver protrusion (I don't know how else to explain it) facing towards the forward of the aircraft?

[WheelPantsOff]

Inches of water?  I'm going to have to google that up.  That's Greek to me.

[PT20J]

10 minutes ago, WheelPantsOff said:

Inches of water?  I'm going to have to google that up.  That's Greek to me.

Manometers use some fluid with a specific gravity depending on the pressure they are intended to measure to keep the apparatus size reasonable. So, for instance, barometric pressure is measured in inches of mercury. Lower pressures are usually measured in inches of water. 

For setting the switch, you can just use the indication on the airspeed indicator.

[Ragsf15e]

3 hours ago, WheelPantsOff said:

 

Just did this.  Gear started to retract at about 95 KIAS.  Is the airspeed safety switch adjustable with the flatblade screwdriver protrusion (I don't know how else to explain it) facing towards the forward of the aircraft?

95 definitely too fast.  If you can adjust it down, that will be awesome!

[PT20J]

13 minutes ago, Ragsf15e said:

95 definitely too fast.  If you can adjust it down, that will be awesome!

The spec is 60 +/-5 KIAS. Kind of hard to see how it would be 150% high without something being grossly wrong. Before cranking on the adjustment, I would check all the pitot and static connections. 

[EricJ]

5 minutes ago, PT20J said:

The spec is 60 +/-5 KIAS. Kind of hard to see how it would be 150% high without something being grossly wrong. Before cranking on the adjustment, I would check all the pitot and static connections. 

I'd think the ASI would be off as much as the switch if it was a pitot pressure problem, unless there's something in the line between the two.

 

[PT20J]

7 minutes ago, EricJ said:

I'd think the ASI would be off as much as the switch if it was a pitot pressure problem, unless there's something in the line between the two.

 

That was my point. Might be an obstruction. On early Js the switch was mounted directly on the back of the ASI, but on later Js, it was mounted on a nearby bracket with some intermediate plumbing. But, most likely, it’s a leak in the diaphragm. Could also be something mechanical with the micro switch. But, the switch itself isn’t going to slip out of adjustment by 150%.

 

 

[RangerM20]

There should be a pitot line drain in the bottom of the forward left wing root.  A static drain at the bottom left of the rear empennage entry, as you are looking in to it.

[EricJ]

1 hour ago, PT20J said:

That was my point. Might be an obstruction. On early Js the switch was mounted directly on the back of the ASI, but on later Js, it was mounted on a nearby bracket with some intermediate plumbing. But, most likely, it’s a leak in the diaphragm. Could also be something mechanical with the micro switch. But, the switch itself isn’t going to slip out of adjustment by 150%.

 

 

A leak in the switch diaphragm would also show up in a pitot leak check, which is pretty easy to do.    I wouldn't be surprised if it just needs adjustment.

[WheelPantsOff]

10 hours ago, PT20J said:

The spec is 60 +/-5 KIAS. Kind of hard to see how it would be 150% high without something being grossly wrong. Before cranking on the adjustment, I would check all the pitot and static connections. 

 

10 hours ago, PT20J said:

That was my point. Might be an obstruction. On early Js the switch was mounted directly on the back of the ASI, but on later Js, it was mounted on a nearby bracket with some intermediate plumbing. But, most likely, it’s a leak in the diaphragm. Could also be something mechanical with the micro switch. But, the switch itself isn’t going to slip out of adjustment by 150%.

 

 

I did have some avionics work done on the airplane earlier this year and I want to rule that out, but I had so many issues with it, I'm having a hard time preventing that.  They also allegedly gave me a IFR/VFR check out of it without any issues.

This is mounted on a nearby bracket.  I traced out all the lines and fittings that I could see and all the B-nuts were at least finger tight and nothing obviously loose.  Is this diaphragm replaceable with a new celophane/rubber?  It's surprisingly easy to access and it seems like the switches are still hard to come by.

[PT20J]

9 hours ago, EricJ said:

A leak in the switch diaphragm would also show up in a pitot leak check, which is pretty easy to do.    I wouldn't be surprised if it just needs adjustment.

I take your point, but a number of people have reported damaged airspeed safety switches after the pitot-static tests. I’m not sure what the failure mode is. Just a week ago a local pilot related to me that he has the exact same problem after a test. He hasn’t taken it back to the shop yet, so we don’t know what the problem is. I suppose it could just screw up the adjustment which is the tension on a spring, but the kind of spring used would be fairly long with fairly soft coils in order to get linearity and it’s hard to see how it would take a set. But, I guess anything is possible.