Looking for M20J airspeed safety switch

[DCarlton]

7 hours ago, PT20J said:

Are you saying you removed the cap and accessed the microswitches, or the large screw on the other side? The large screw adjusts the spring tension to set the calibration. 
https://www.knr-inc.com/shop-talk-articles.html?view=article&id=93&catid=25

 

It's been several years.  During an owner assisted annual, I know for a fact I removed the switch.  I know for a fact my mechanic and I opened the switch, dropped in a touch of lubricant, cycled it on the bench and got it working.  I think we removed the big screw that adjusts the calibration, then readjusted the unit back on the aircraft.  It's worked fine ever since.  And yes, this was the newer switch purchased from VEP several years before that.   BTW, great article; particularly the comment about don't be afraid to take it apart.  

Edited August 21, 2023 by DCarlton

[Aerodon]

This is what the switch looks like inside the box. Two micro switches epoxied to a plate.  The diaphragm pulls the actuator away from the micro switches.  My main micro switch works, the auxiliary switch does not.  I am trying to use the auxiliary switch for both a flight timer clock and an airborne sensor for a transponder.  It looks like I might be able to get the auxiliary working by adjusting the micro switch ‘further away’ from the actuator with the small set screws.

 

aerodon

 

[Vance Harral]

On 8/18/2023 at 12:53 PM, KSMooniac said:

I half-watched an EAA webinar on Wednesday evening on the topic, but haven't tried it myself yet.  I would encourage every owner to go watch it as I believe they're archived, and count for WINGS credit in case that is useful for anyone.  I believe it was developed for exactly this type of situation.

I attended that same webinar, and came away from it somewhat pessimistic about the ability of VARMA to do much good for Mooney owners, because Mooney is at least theoretically still in the business of supplying parts.  Even when the part in question was actually manufactured by someone other than Mooney, it sometimes has a Mooney part number in the IPC, and I think that's going to be a problem.

To wit: the guys running the webinar stressed that you won't get a VARMA letter for a part which is purportedly available from the OEM of your airplane, because the FAA doesn't want to be seen as taking business away from the manufacturer.  They framed it as "you won't get a VARMA letter for a part you just think is too expensive from the OEM".

I get that, but during the Q&A, there were apparently dozens of people who had the same question as me: namely, what if a part is only theoretically available from the OEM, but not actually available in practice?  This is the situation we have with lots of Mooney parts today: intake boots, yoke shafts, etc.  If you actually ask Mooney to sell you one of these things, you often get a song and dance about indefinite lead times, the need to accumulate enough orders to justify making a run of parts, and so on.  Your aircraft could easily be AOG for months waiting on such a part.

I was disappointed that the VARMA guy who answered the question seemed to be unaware of this problem.  He seemed a little surprised by the question itself.  He tried to give a hopeful answer, but it was a vague thing like, "Oh, well, I would like to think that's the kind of thing we could work out a solution for."  It was clear they hadn't really considered this theoretical vs. actual availability problem while building the VARMA framework.

Anyway, maybe I'm being too pessimistic.  But the way I see this going down is that Mooney isn't going to admit they can't supply parts until/unless they actually go bankrupt, and without such an admission, the FAA isn't going to give you a VARMA letter for anything with a Mooney part number in the IPC.

[PierreL]

Many thanks for all your replies. I will put the plane on jacks in the next weeks and first try to swap the switches. I will let you know if I solved my issue.

Does anyone already replace such airspeed safety swith by a TCW USW-1 or equivalent?

https://www.tcwtech.com/product/universal-switch-airspeed-kit/

Looking at the specs it should do the job.

[ArtVandelay]

Many thanks for all your replies. I will put the plane on jacks in the next weeks and first try to swap the switches. I will let you know if I solved my issue.
Does anyone already replace such airspeed safety swith by a TCW USW-1 or equivalent?
https://www.tcwtech.com/product/universal-switch-airspeed-kit/
Looking at the specs it should do the job.

It’s for experimentals only, which brings up the question, has anyone been able to use experimental parts in a certified aircraft, especially for critical applications?

[A64Pilot]

57 minutes ago, ArtVandelay said:

It’s for experimentals only, which brings up the question, has anyone been able to use experimental parts in a certified aircraft, especially for critical applications?

You can use anything IF you get it field approved, I know I could have with my old inspector because we had an excellent relationship, now? most probably not. Of course your going to have to come up with instructions for continued airworthiness etc.

However if I understand the switches function I’m not sure I’d say it’s critical, all it does is stop retraction from happening until a certain airspeed? Now if it was required for them to come down yes it would certainly be critical, but is retraction a critical function?

But that’s of course a judgement call, and no one is ever chastised for being conservative, which is why I think we see so many 337’s for things that in my opinion aren’t major

[Aerodon]

If you look at the picture I posted above, you will see each microswitch has an adjustment screw.  One side was working fine, the other side was 'always open'.  About a turn of the adjusting screw, and I could hear the microswitch close.  I had to grind about one thread off the adjusting screw to get it to work.

Aerodon

 

[KSMooniac]

One trick to think about when fiddling with these switches... you can blow up a party balloon and slip it on the pitot tube to pressurize the system enough to move the ASI into range without damaging the switch.  DO NOT USE SHOP AIR like some ham-fisted mechanics do, or you'll be shopping for another switch.

[Aerodon]

OK, Scott, you sent me down a rabbit hole.

A person can 'blow' up to 2.8 psi

A party balloon is 0.25 psi

The pressure switch is rated to 50" water, or 1.8 psi

65 knots is 0.2 inHG or 0.1 psi

So yes, be careful with the switch.

Aerodon

 

 

[1980Mooney]

On 8/22/2023 at 5:59 AM, ArtVandelay said:

It’s for experimentals only, which brings up the question, has anyone been able to use experimental parts in a certified aircraft, especially for critical applications?

 

On 8/22/2023 at 7:01 AM, A64Pilot said:

You can use anything IF you get it field approved, I know I could have with my old inspector because we had an excellent relationship, now? most probably not. Of course your going to have to come up with instructions for continued airworthiness etc.

However if I understand the switches function I’m not sure I’d say it’s critical, all it does is stop retraction from happening until a certain airspeed? Now if it was required for them to come down yes it would certainly be critical, but is retraction a critical function?

But that’s of course a judgement call, and no one is ever chastised for being conservative, which is why I think we see so many 337’s for things that in my opinion aren’t major

If you are struggling to climb in marginal conditions with the landing gear down (high DA, engine issues, high GW, etc), I would say the inability to raise the gear could be "critical". 

And how would this different from buying "Experimental Only" avionics and installing them?  It's not allowed for avionics (which are "critical") so I can't believe that it could be done here.  

[1980Mooney]

2 hours ago, KSMooniac said:

One trick to think about when fiddling with these switches... you can blow up a party balloon and slip it on the pitot tube to pressurize the system enough to move the ASI into range without damaging the switch.  DO NOT USE SHOP AIR like some ham-fisted mechanics do, or you'll be shopping for another switch.

 

2 hours ago, Aerodon said:

OK, Scott, you sent me down a rabbit hole.

A person can 'blow' up to 2.8 psi

A party balloon is 0.25 psi

The pressure switch is rated to 50" water, or 1.8 psi

65 knots is 0.2 inHG or 0.1 psi

So yes, be careful with the switch.

Aerodon

Here is how Clarence raises the pitot pressure to test ASI and airspeed switch (wish he was still here providing useful advice):

You can easily prove that it works.  Get a 4’ length of 1/4” surgical tubing, some vinyl electrical tape and 2 clothes pins.  About 3/4” back from the tip of the pitot head there is a small hole on the bottom, wrap a few layers of tape around and covering the hole.  Stretch the surgical tubing onto the tip of the pitot head, place one clothes pin at the end of the tubing, pinching the tube closed.  

Slowly roll the tubing around the clothes pin, this will increase the pitot pressure causing the airspeed indicator to rise. It takes very little pressure to move the ASI and little more to damage it.  Use the second clothes pin to pinch the tube, blocking the pressure in the system.  In a tight system when you stop rolling the ASI needle will stop moving and will hold steady. Typically you want to see less than 10 kits per minute loss rate.  Unroll the clothes pin slowly to avoid damage to the ASI.

 If it falls you have a leak to locate and repair.  

Make sure that the gear selector switch is DOWN and the gear actuator circuit breaker is pulled.  If your plane has an airspeed safety switch and the gear switch is in the wrong spot the gear will retract.

Clarence
 

 

Edited August 23, 2023 by 1980Mooney

[A64Pilot]

2 hours ago, 1980Mooney said:

 

If you are struggling to climb in marginal conditions with the landing gear down (high DA, engine issues, high GW, etc), I would say the inability to raise the gear could be "critical". 

We can what if anything until the ONLY answer is to not fly, in your scenario I’d push the red button, I’d guess that’s why Mooney included it, or go around and land. I’m so gear paranoid I’d probably go around and land.

It depends on the professional opinion of the installer, and you know what? You can never be wrong if you insist on only OEM parts, and by not you open yourself up to liability. Only thing that makes you even have one in my opinion is type design, quite a few aircraft don’t have any kind of disable mechanism for the gear, the 210 I used to fly I’m pretty sure didn’t, to do a retract test with it on jacks all you had to do was put the gear switch up, you didn’t have to spoof a squat switch or push a bypass button.

I post this every now and again and while I’ve not gone through it for this specific question (can I use an experimental part?) I suspect as long as the original part no longer exists and the experimental performs the same function, maybe you can. Sure your going to have to jump through some hoops, but what other option do you have?

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_23-27.pdf

 

This AC is applicable to ALL Mooney’s even the last ones built.

[A64Pilot]

2 hours ago, 1980Mooney said:

 

Here is how Clarence raises the pitot pressure to test ASI and airspeed switch (wish he was still here providing useful advice):

You can easily prove that it works.  Get a 4’ length of 1/4” surgical tubing, some vinyl electrical tape and 2 clothes pins.  About 3/4” back from the tip of the pitot head there is a small hole on the bottom, wrap a few layers of tape around and covering the hole.  Stretch the surgical tubing onto the tip of the pitot head, place one clothes pin at the end of the tubing, pinching the tube closed.  

Slowly roll the tubing around the clothes pin, this will increase the pitot pressure causing the airspeed indicator to rise. It takes very little pressure to move the ASI and little more to damage it.  Use the second clothes pin to pinch the tube, blocking the pressure in the system.  In a tight system when you stop rolling the ASI needle will stop moving and will hold steady. Typically you want to see less than 10 kits per minute loss rate.  Unroll the clothes pin slowly to avoid damage to the ASI.

 If it falls you have a leak to locate and repair.  

Make sure that the gear selector switch is DOWN and the gear actuator circuit breaker is pulled.  If your plane has an airspeed safety switch and the gear switch is in the wrong spot the gear will retract.

Clarence
 

 

I just got through doing that for someone, he brought the tubing, except I used hemostats, surely ever mechanic has a collection of stats.

He explained it to me, otherwise I would have used the old spygometer pump I have for inflating my door seal, just go very slow.

[A64Pilot]

2 hours ago, 1980Mooney said:

And how would this different from buying "Experimental Only" avionics and installing them?  It's not allowed for avionics (which are "critical") so I can't believe that it could be done here.  

The difference is that Certified Avionics are available, if for some bizarre reason and I can’t think of one that the only option to return the aircraft to airworthiness is with an Experimental avionics then I think you would have a shot.