Tommy Posted October 7, 2014 Report Posted October 7, 2014 Yo fellow Mooniacs! When I first got my M20J (1981) the autopilot (KFC200) HDG and Alt Hold are both working beautifully. Lately I have noticed that the alt hold - the HDG is working perfectly - isn't working any more for reasons unknown (I never abused the system and all indications are normal). It doesn't hold and when I press UP/DWN rocker switches (with or without Alt Hold mode on), the auto pilot does nothing. Does anyone know what would've caused this? Is there anyway to reset Autopilot KFC 200? Thanks! Tommy Quote
PTK Posted October 7, 2014 Report Posted October 7, 2014 Tommy, what does the flight director do? Next time you fly pay close attention to the FD. If the FD commands proper pitch but autopilot doesn't react you need to look at the pitch servo. The FD is the brains and the autopilot servos are the muscles. Quote
Tommy Posted October 7, 2014 Author Report Posted October 7, 2014 As far as I can tell, it looks like FD isn't commanding any pitch change. What does it mean? The whole system was working perfectly fine three weeks ago. Quote
Marauder Posted October 7, 2014 Report Posted October 7, 2014 As far as I can tell, it looks like FD isn't commanding any pitch change. What does it mean? The whole system was working perfectly fine three weeks ago. If it functions like the STEC products, it means there is no valid signal to command. On my plane, I have an aaspen displaying the flight director. When I had a problem with the AP, the bars never came up. Have you tried other glide slope signals? Perhaps from another approach? Quote
KSMooniac Posted October 7, 2014 Report Posted October 7, 2014 It s an old analog autopilot so there isn't any resetting or rebooting to be done. Time for a trip to the avionics shop I'm afraid. The computer can be sent to a specialist for bench testing and I suspect the problem might be in there if your FD is not indicating any commands. Sent from my VS985 4G using Tapatalk Quote
Bill Dunn Posted October 7, 2014 Report Posted October 7, 2014 I would have to look at your plane to be sure but it sounds like you don't have any pitch command. I have the KTS 150 test set here at the shop for KFC 200 autopilots. In fact I have a beech hooked up to it right now. If you are close to west Chester, PA I could schedule you in to take a look at it. Our number here is 610-436-1200 Ask for me. Quote
Bob_Belville Posted October 7, 2014 Report Posted October 7, 2014 B26, I may have asked this before, I know you have flight director with your Aspen, do you know if that feature requires an STEC 55 or 60? I have a 50, no alt pre-select. Quote
Marauder Posted October 7, 2014 Report Posted October 7, 2014 B26, I may have asked this before, I know you have flight director with your Aspen, do you know if that feature requires an STEC 55 or 60? I have a 50, no alt pre-select. Bob -- I just pulled up the brochures for the 50 you have and the 60-2 that I own. The 50 brochure doesn't show the ST-670 as an option while the 60-2 does. http://sharepoint.s-tec.com/Documentation/Shared%20Documents/Product%20Brochures/sys_40-50.pdf http://sharepoint.s-tec.com/Documentation/Shared%20Documents/Product%20Brochures/sys_60-2.pdf Looks like the 55 and up are the only ones compatible with the flight director. 1 Quote
Bob_Belville Posted October 7, 2014 Report Posted October 7, 2014 I note "computers" in the circuit between the A/P panel and the roll and pitch servos on the 60-2 and not on the 50. Guessing that's the key. Quote
Marauder Posted October 7, 2014 Report Posted October 7, 2014 I note "computers" in the circuit between the A/P panel and the roll and pitch servos on the 60-2 and not on the 50. Guessing that's the key. Looks that way. The flight director is nice especially if you are flying a missed. I have the ability to turn on the flight director without the autopilot servos engaged. I have never flown a double cue FD but I am told that my single cue is much easier for some pilots to comprehend. Quote
Piloto Posted October 7, 2014 Report Posted October 7, 2014 I had exactly the same problem and after two months chasing it found the cause. When the CWS switch on the yoke is pushed in it will disable pitch and altitude hold but not lateral control. This allows the pilot to change altitude quickly with the yoke without loosing lateral/roll control. Check the CWS switch and its wiring in the yoke. If the CWS wire is grounded or the switch is stuck the altitude hold is disable but there is still lateral control. The wire could be chafing anywhere from the yoke arm to the shaft end. Verify the voltage on the CWS changes when depressed. In my case the wire was chafing on the yoke pin bolt. I had never used the CWS switch before since I use the A/P UP/DN rocker switch always. It is smoother, more precise and next to the throttle. I removed the CWS switch since I never use it. José Quote
Tommy Posted October 7, 2014 Author Report Posted October 7, 2014 I don't think it's the CWS. Becuase my autopilot still holds HDG and will turn to new HDG bug. I thought it won't do that if you the CWS is engaged. Just wondering what would be the easiest and quickest test to differentiate the causes (ie. servo vs non servo) and just exactly what are the non- servo problems that can cause this symptom? Ie. no pitch command (assume FD didn't command at all when UP/DN switches are pressed with or without ALT Hold)? Thanks guys! Quote
PTK Posted October 7, 2014 Report Posted October 7, 2014 Tommy, take a flight and pay attention to the FD. If indeed it does command a pitch change then look at pitch servo first. If not look at computer first. Computer problems are rare relative to servo issues. So really be certain as to what the FD is doing. Quote
Piloto Posted October 7, 2014 Report Posted October 7, 2014 In my case the CWS wire chafing was intermittent and only in flight due to engine vibration. If the CWS is just pressed momentarily it will disable altitude hold but not heading. Mine (Century 31) will still indicate ALT but altitude was drifting all over. Before my finding I spent $1,000 on A/P computer and pitch servo for overhaul at Autopilot Central. They were honest enough to tell me they could not simulate the symptom I was experiencing. Good quick honest service. José Quote
Tommy Posted October 8, 2014 Author Report Posted October 8, 2014 Forgot to mention, prior to this, the trim warning light will come on fairly frequently - especially if the aircraft is out of trim by a reasonable margin. Is this indicative of a trim servo problem? Ps. I had no issues using the manual electric trim. Quote
Tommy Posted October 10, 2014 Author Report Posted October 10, 2014 Ok done a ground test with my KFC200 on a 1981 J. Time to dig your guys' brain! Observations 1) manual eletric trim (with yoke) works and will disengage ap 2) FD bar shows commanding aircraft pitch in the right direction when vertical pitch command is pressed on the Mode Panel (with and without AP AND with and without Alt engaged) BUT the trim wheel is not turning at all and the trim indicator shows no movement. 3) and when CWS is pressed the FD bar reset. 4) the red TRIM warning doesn't flash when "test" button is pressed. It used to but seems not any more in the last few flights which corresponds to the failure of alt/pitch control 5) the HDG hold worked perfectly This is in the context of perfectly working AP but with intermittent TRIM flashes and disengagement of AP (especially if it is quite out if trim) So is it my trim servo? Thanks guys! Quote
Tommy Posted October 10, 2014 Author Report Posted October 10, 2014 And I will be doing an actual flight test today Quote
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