ALT AIR coming on more easily

[dkkim73]

Hi all, 

During transition training, I was taught to bring the throttle in slowly above 2300 (after static run up prior to brake release) to avoid opening the ALT AIR door too much on the ground. 
In the last weeks to month or two I've noticed it just comes on more easily even if I'm very slow, and stays on longer in the climb. 

Just had my Challenger air filter serviced, a bit too much oil I think, but the problem isn't tightly correlated with this work. 

So I'm thinking about the magnet that keeps it closed, and the spring. I found some force #s in the maintenance and service manual. Ordered a little digital push/pull gauge. Anyone testing this themselves or know how much work it is to expose? If it's a thrash I can ask them to do it at annual next month. 

Thanks for any thoughts, 
David

 

[dkkim73]

Update on this. I got a digital force meter and tested the door. Had to correct for a tilt but it looks like the door opens at <=4lbs, where spec is 4.5-7.5 lbs. I don't see anything mechanically wrong (ie. debris causing a gap or non-contact between the magnet and plate). 

The door is a flap that in it's fallen position brings a little plate against another plate screwed to a permanent magnet. 

Has anyone repaired one of these or replaced the magnetic catch? The smallest part (the catch that looks like a cabinet catch) is $376 and 10 week lead time to manufacture. An A&P suggest OPP, rebuilding the magnetic part, if I felt up to it. I figure the most challenging part would be getting a magnet of the right strength to get the opening force right. 

Photos posted for orientation. The catch is the little "hutch"-like structure screwed to the frame. 

Would also be open to just getting a surplus assembly but don't see any listed online right now. 

D

[Schllc]

I had this issue on two different planes. Both times it was the indicator sensor, not the actual door opening.  Adjustment fixed it both times. 
I did not do it myself however.  Brian K fixed the last one for me.  
mine was only failing in the initial phase of take off and climb. It usually self corrected before reaching 3k

[N201MKTurbo]

Those cabinet latching magnets require two plates to function properly. I think you are missing one of the plates. They require two plates to complete the magnetic circuit from north to South Pole on the magnet. Go to the hardware store and buy a magnet to harvest a new set of plates and consider replacing the striker bar while you are at it.

[N201MKTurbo]

On closer examination of your picture, your magnet may have both plates stacked on one side of the magnet. If that is the case, take it apart and put it together right. The drawing from the manual shows the two plates correctly.

[dkkim73]

@N201MKTurbo That is a good observation! Subtle on the drawing but makes sense physically. I had some other photos from that day, attached here. I think there is only one discrete plate, as you thought initially. I suppose the bracket might help to conduct flux from the other pole, but it's not quite the right geometry and has "legs". Plus it might be made of something different. 

 

@Schllc Do you recall what was the issue with the switch? Was it just a slightly change in position, inertia causing the contact to flicker, etc? 

[dkkim73]

Interestingly, the LASAR picture of the replacement part looks similar. FWIW there are two parts, one supercedes the other: 

 

https://lasar.com/doors/latch-replacement-for-pn-600168-501-600296-501

 

[Schllc]

It was repositioning the switch and cleaning contacts. 
the door was not actually opening, I was just getting erroneous indications that it was. 

[N201MKTurbo]

With one plate, the holding force will be very low. 
 

My plane has the same kind of magnetic latch on the alt air door. It has the two plates. It is a lot smaller than yours, maybe 6-8 sq in. It takes a good push to open it. As big as yours is, a dirty air filter would open it.

[N201MKTurbo]

[N201MKTurbo]

Maybe a call to Mooney is in order.

[dkkim73]

1 hour ago, N201MKTurbo said:

Maybe a call to Mooney is in order.

Do you mean to discuss the appropriate configuration and clarify the right part? I had not thought of that, instead calling LASAR. 

Mooney are the ones who have the production lead time mentioned above. 

I see your point about lesser force without a second plate. 

Anyone here disassembled one of these? I assume you need the air box out to get sufficient exposure... Maybe during the upcoming annual. 

Thank you guys, BTW!

D