century 41 auto pilot

[peter west]

have a 1979 mooney 201 which came with century 41 auto pilot from factory. auto pilot has issue with altitude hold, gets pitchy, only holds altitude for a few minutes at a time, then cannot hold the pitch at proper attitude, then it pitches down, the aircraft loses 300 -400 feet or so all at once, and at that point i have to uncouple auto pilot.  have had brain box sent to auto pilot central in tulsa, they say nothing wrong with brain box.  have no idea what to do about this, most shops will not work on this brand, aircraft based in denver,colo.  

[Jake@BevanAviation]

Honestly probably a transducer issue.  I don't like to work on the 41 as they are full of ribbon cables and a lot of the parts are not available any more.  The last 41 I sent to Century came back with a 9k repair estimate.  It had a failing transducer that would produce intermittent oscillations and multiple ribbon cable problems.

[Tom 4536]

11 hours ago, peter west said:

have a 1979 mooney 201 which came with century 41 auto pilot from factory. auto pilot has issue with altitude hold, gets pitchy, only holds altitude for a few minutes at a time, then cannot hold the pitch at proper attitude, then it pitches down, the aircraft loses 300 -400 feet or so all at once, and at that point i have to uncouple auto pilot.  have had brain box sent to auto pilot central in tulsa, they say nothing wrong with brain box.  have no idea what to do about this, most shops will not work on this brand, aircraft based in denver,colo.  

Last year I had the same problem with my Century 41 in my 1979 231. We sent all the autopilot components to Executive Autopilots twice and never solved the problem. I gave up and had a GFC500 installed. Hope you have better luck than I had.

[buddy]

When I had my 1980 M20J with the century 41 auto pilot it seemed all my pitch problems lead back to a pick off the attitude indicator. When I had it in altitude hold every once in a while it would pitch up and I had to disconnect the A/P. I flew the airplane out to Century and they repaired repaired the problem and told me it was a pick off the attitude indicator. Years later I had the same problem and after about a month of trouble shooting at the avionics shop they finally sent out the attitude indicator for repair and that solved my problem. Not many shops work on the A/P. PM me with your phone number and we can talk.

[Tom 4536]

When my Century 41 failed, it was a week prior to a panel upgrade to GI275s. So while the Century 41 was at Executive Autopilots, the old AI was being replaced with a GI275. The Century 41 had the same problem even with the new AI.

[Warren]

Just replaced an attitude indicator on a 1979 M20K Century 41 system.  The attitude indicator (old vacuum unit) was failing causing all kinds of problems.  Replaced the attitude reference with with a GAD 43 (attitude translator for a legacy G500).  The Century 41 now flies like new, maybe better, with a digital attitude source.

So it is possible the attitude indicator is the problem.  In our case, the attitude indicator was obviously failing.  Slow to erect, slightly off at times, more at other times,...  If there are any obvious problems with the attitude indicator start with replacing that.

[Warren]

First let me state that I don't have a lot of experience with this autopilot - so, these are my best guesses based on the wiring diagrams for the G500 and my limited experience (sample size of one plane).

Heading data is sent to the autopilot via a heading error signal and course data is sent on a separate line for course error (guessing this feeds the NAV mode in the autopilot).

1.  The HDG and GPSS from the G500 are fed through the HDG mode in the autopilot.  When you make the switch from HDG to GPSS, leave the autopilot in HDG mode and it will provide the precise GPSS you are looking for.  There is also a place to calibrate the rate of turn conversion from GPSS if the turns are too aggressive or lethargic in GPSS mode.  You will need a dealer with an Installer Unlock Card to access this setting, but know it can be adjusted.

2.  The course guidance from the G500 should be where the NAV heading is fed (some speculation here) and may be the source of your error.  I would have your shop check the integrity of this wire to ensure it is not damaged.

Hopefully this is somewhat helpful for general understanding.  Maybe someone who knows these better can help with more detail @Jake@BevanAviation (please help/correct my statements as needed).

Warren

[Jake@BevanAviation]

@philip_gWith a Century 41 if you have a flashing NAV, APPR or GS annunciation it typically means the computer is not seeing a valid signal for navigation and will continue to flash the associated mode till the signal is valid.  Depending on what mode of operation you are wanting, the computer should be getting a lateral flag valid for lateral tacking and a vertical flag valid for vertical guidance.  These connections should be depicted in the IM for the associated Garmin interconnect.  The valid information should come out of the GDU to the C41 computer.

Edited August 12, 2021 by Jake@BevanAviation