One_Lima_Bravo Posted March 11, 2011 Report Posted March 11, 2011 My 1970 M20/F has the Postive Control system by Brittain. I've had the Mooney for 4 years and the PC has always worked great. Now, for some reason that neither my mechanic nor I can understand, the PC stays engaged even when I depress the PC button on the yoke, or pull it completely out. The mechanic cleaned the vaccuum lines and said he fixed it. I took it up and it is worse than ever. I have to use two hands to turn the yoke, with or without the button depressed, and my Auto Pilot won't track correctly. When the system was working correctly, even when it was engagement I could easliy over come it with on hand. Now I have to use two hands to even get it to move a little. On the ground it is difficult but once I have vaccuum built up in the air it is really bad. Has anyone else ever had this problem? Any suggestions I could pass on to my mechanic. Thanks, Quote
takair Posted March 11, 2011 Report Posted March 11, 2011 Yes, when I bought my plane (64E) I could not disengage it. Mine has the pneumatic relay/disconnect. It had dust built up on the vent to the point where it would not see atmospheric on the other side of the relay. I don't recall all of the details, but basically it required a cleaning. Other things to look at are a kinked line between the relay and the switch. This would act such that you could not disconnect. Since yours was working well....I would concentrate on that. If anybody was behind the panel, this especially easy to kink. The last thing I can think of is that the relay is simply stuck on. This would require a teardown and cleaning. It is not complicated, but it is rather sensitive. Feel free to PM me and I would be happy to talk to your mechanic about it. Have had it apart a few times over the years. Quote
One_Lima_Bravo Posted March 11, 2011 Author Report Posted March 11, 2011 Thanks, I'll pass it on to my Mechanic and see if he can get this thing figured out. Quote
scottfromiowa Posted March 11, 2011 Report Posted March 11, 2011 You've grounded your plane until this is corrected, right? Based on your posts I wouldn't fly the plane until corrected. I would question whether something else is wrong as you should be able to defeat the PC/the effort should NOT be such that it would require two hands under any circumstances. I can push against my PC and it's stiff, but NOT to the degree you are talking. Be careful... Quote
N601RX Posted March 11, 2011 Report Posted March 11, 2011 Quote: One_Lima_Bravo My 1970 M20/F has the Postive Control system by Brittain. I've had the Mooney for 4 years and the PC has always worked great. Now, for some reason that neither my mechanic nor I can understand, the PC stays engaged even when I depress the PC button on the yoke, or pull it completely out. The mechanic cleaned the vaccuum lines and said he fixed it. I took it up and it is worse than ever. I have to use two hands to turn the yoke, with or without the button depressed, and my Auto Pilot won't track correctly. When the system was working correctly, even when it was engagement I could easliy over come it with on hand. Now I have to use two hands to even get it to move a little. On the ground it is difficult but once I have vaccuum built up in the air it is really bad. Has anyone else ever had this problem? Any suggestions I could pass on to my mechanic. Thanks, Quote
rdav Posted March 11, 2011 Report Posted March 11, 2011 I agree with Scott. I've never had to use much force to overcome the PC .. could this be some other problem in the flight control system. Definitely something to test while taxiing in circles rather than in the circuit! Quote
One_Lima_Bravo Posted March 12, 2011 Author Report Posted March 12, 2011 I have "grounded" my Mooney until the problem with the PC is resolved. I'll also post the problem resolution once it is known, fixed, and validated. Thanks everyone for your help. I'll be speaking with my mechanic today to see if he's got the any updates on my plane. Quote
danb35 Posted March 12, 2011 Report Posted March 12, 2011 If you haven't already contacted them, you can get all the service/maintenance/installation manuals from Brittain for the asking. http://www.brittainautopilots.com/ Quote
planebones Posted March 13, 2011 Report Posted March 13, 2011 On my "C" model the PC's control valve (aft of firewall left side) became "stuck" I removed it cleaned it, polished "shuttle valve" and reassembled and now works perfect. Also check that small hoses are not cracked or loose at the fittings. Ken A&P/IA Quote
flight2000 Posted March 13, 2011 Report Posted March 13, 2011 You can also download the PC manual from here as well. http://www.67m20e.com/Manual%20No.%2011990%20Mooney%20PC%20Operation%20and%20Service%20Instructions.pdf Quote
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