Lima Whiskey

I thought I would post a recent problem we had with our 1980 M20J. It started out with the NAV flag on our HSI starting to randomly popping in and out. However, the autopilot continued to fly the proper guidance from our GNS530W. Everything appeared to be working properly from the self-test that the 530W runs when it boots up. Then things got even crazier. On a night flight home from visiting our grandson in Dayton, Ohio, at 9,000 feet, in and out of IMC, the autopilot dropped both ALT and NAV but the power to the unit stayed engaged when I turned on the Instrument Panel Light Rheostat. It didn't happen immediately but about 15 seconds after I turned on the Rheostat. I turned the Autopilot off and on, reengaged ALT and NAV, it stayed up for a couple seconds and then dropped. At the time, I didn't realize that it had anything to do with the Rheostat, so I ultimately ended up hand flying the last 1.5 hours of the flight, in the dark, in and out of IMC (an aside - I know some will argue the wisdom of flying in IMC at night in a single engine plane - I get it - it wasn't fun - and if the big fan at the front of the plane stopped spinning it would have been less fun - but that isn't what this post is about). The other thing that I need to add to this little mystery is that since we purchased the M20J back in 2018 the Instrument Panel Rheostat was either off or on, there was no dimming. The panel lights didn't turn on until the rheostat was turned all the way up. After a visit to the avionics shop, a flight with the technician to show him what was happened (where some times the NAV and ALT dropped in the autopilot and sometimes the entire autopilot turned off), and 8 hours of shop time trying to diagnose the problem, the problems were solved. First, the avionics tech discovered that there was no ground to the Trim Power Switch. Adding a ground stopped the autopilot from shutting off when the Instrument Panel Light Rheostat was turned on. It also stopped the NAV flag from randomly popping in and out. I don't know the why behind it all, but the ground wire fixed it. Second, when the avionics tech installed a new rheostat, the instant he turned it on, he "smoked" the rheostat. Apparently there was too much power coming from somewhere. He ultimately discovered that the power lead to the transistor which controls the dimming system had become disconnected. This transistor was located on the right side of the panel behind the circuit breaker panel. Once he connected the wire, the new rheostat dimmed everything properly. Hopefully this post is helpful to someone who experiences the same problem and they will be save 8 hours of troubleshooting and about $1,000. I am extremely thankful to the guys at our avionics shop, it took some time but they didn't give up.

I wish I would have known earlier also. I should have posted something looking for the parts. I will do so in the future.

I wanted to share somethings that I learned this past week about the yoke mounted Trim Interrupt switch on our club's 1979 M20J. The red button on the trim interrupt switch was broken off accidentally by one of our club members. It immediately disabled the electric trim and as a result the autopilot. I was under the impression that the Trim Interrupt switch not only was used to stop a runaway trim but also to disconnect the autopilot, however we never really used the button. We always disconnected the autopilot with the on/off switch on the unit. When our mechanic pulled out the switch it was stamped with part number C2003R - which turns out you can get from Textron for $99.95. C2003R has four contacts. As I understand it, pins 1 and 2 are normally closed and pins 3 and 4 are normally open. Pins 1 and 2 are used for the Trim Interrupt and pins 3 and 4 are used for the autopilot disconnect. So when you press the button it takes power away from the trim and also sends a signal to the KAP 200 to disconnect. However, our switch only had wires to pins 1 and 2 - the Trim Disconnect. When the mechanic installed the switch the electric trim began to work and we could use the autopilot. If anyone can tell me the thought process behind the trim interrupt switch, I would appreciate it. It only stops a runaway trim when it is depressed. As soon as you release the button the runaway trim would continue. It seems to me that the only way to really stop the runaway trim is to turn off the trim switch on the panel. So the yoke mounted trim interrupt switch seems kind of useless. Maybe the idea is that you depress the yoke mounted switch and then you immediately switch off the panel mounted trim switch. I share all of this because we ended up spending $600 on the repair. Textron had the part on backorder until the middle of August (and I have an 18 day East Coast to West Coast and back trip planned for this coming Friday) so we had to get the switch from another supplier. At the end of the day we paid $360 for the switch and expedited shipping and then the labor. Hopefully this helps someone in the future. I would be interested if anyone has any knowledge on how to make the switch actually disconnect the autopilot. I would imagine that two wires need to be run from the autopilot control unit to the yoke and soldered to pins 3 and 4 of the C2003R switch, but I don't have any kind of wiring diagram for the connectors on the back of the KAP 200 control unit. This is my first post... so go easy on me :-)

A guy in our M20J club accidentally broke the Autopilot Disconnect/Trip Interrupt switch for out King Autopilot 200. The switch C2003R is handled by Textron and sells for $99.95 each. Unfortunately the switches were backordered until mid-August and I am leaving on a cross-country trip to California next Friday. Many thanks go out to Bob Weber at webairconsulting.com 616 822 1999 for helping our mechanic figure out how to get a replacement switch. Even though Bob didn't have a switch, he helped us find one. The good thing is we have replaced the switch. The bad thing is that we had to pay $360 for it (without labor).

This is my first time using the forum. Last week, after doing several practice Instrument approaches each ending with missed approaches, with the two other partners in our 1979 M20J, we noticed the engine running rough when we were taxing back to the hanger. It didn’t seem too bad so we figured we would diagnose prior to the next flight. Also, we didn’t notice it when we were flying After a week of rainy weather, I pulled her out of the hanger, performed a preflight and fired her up. It was running super rough. When I throttled up the electronic rpm gauge would go crazy (running all the way up and then all the way down, even cutting out). Clearly I wasn’t going to fly it. When the mechanic on the field checked it out, he found the plugs were fine and so were the mags. What wasn’t fine was that 6 of the 8 bolts on cylinder two were missing and/or sheared off. Of the remaining, one was tight and the other finger loose. We bought the plane 18 months ago with an overhauled engine that only had 100 hours on it. We also had an annual done in August 2018 at a Mooney service center. The engine now has about 250 hours on it Any ideas how this happened? Did the overhaul guys mess up? Do the cylinder head bolts get checked on the annual? Is it possible that we have been doing something wrong with engine management that would have contributed to this? And most importantly, how do we make sure this doesn’t happen again? It could have been catastrophic if the remaking bolts would have left loose in flight.