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Century IIB autopilot fixed

Just a small write up about how I fixed my Century IIB AP.

For a while, I had no hopes of getting my 50 year old Century IIB Autopilot to work again. The AP was installed in my 1969 Piper Arrow 200 original from factory. It would hold the wings level or keep a heading for about 10 seconds before it started a sharp bank to the left and initiate a spiral dive. Scary stuff. So I marked it inop and burried my dreams of having a working AP. That was until I got in touch with a company called SIBA Avionique in France.

They are a certified avionics repair shop and century AP are in their capability list. I pulled the AP controller and sent it to them. They tested, replaced the failed power transistors, re-certified it with Form 1 and sent it back. Total bill was 600 euros including shipping. I highly recommend the guys at SIBA Avionique. Had I sent the controller for testing/fixing to Straubing in Germany, it’d have easily costed a 4 digit figure plus a few weeks of lead time. SIBA returned the controller within the same week.

2 weeks ago I did the calibration flight according to Century manual. There are 4 adjustment screws behind the front cover on the controller. The first one from the left adjusts roll threshold (fixed the wingrock/oscillation issue), the 2nd is for left bank angle (should be 20deg for turns greater than 90 degrees), 3rd one is for heading centering adjustment and the last one is for right bank angle. The entire calibration procedure is very well detailed out in the Century AP manual. It was a bit of back and forth playing with these screws as somehow they seem to be effect each other. It seems to work better when you adjust left bank first, then center, then right bank.

Anyway, now the AP on my old bird is able to keep a heading within +/-1 deg, with zero wing rock and is even able to track localizer or vor signals. It is amazing how much you can do to get the old avonics back in shape if you do some proper research and know what your are doing. If anyone needs more details including the century AP calibration manual, just drop me a message.


Thanks for sharing.

It is nice that there are shops that still wants to deal with old autopilots.
But I must say that I got a quote from Straubing for one old similar AP, Navomatic 300A:

“The standard price for repair is between 400,- and 1000,-€”


With an old, but faithful Century IIB autopilot which is still working well it is good to know – if the need arises – that there are repair shops out there who can assist, if need be.
On the basis of ‘KISS’ (‘Keep It Simple, Stupid’) my Century IIB autopilot together with my basic System 60 PSS Alt Hold, has served me faithfully and safely for hundreds of hours in my PA28 Arrow IV.
Why go for sophistication/complication when ‘simple’ works best?

Rochester, UK, United Kingdom

Did anyone make Century IIB work with Garmin G5?


@By9468840, I didn’t make it work, but it is supported by G5. I originally intended to interconnect them, but am now tempted to go for GFC 500 instead, it’s such an excellent value for its price. On the other hand, maybe I ought to try the Century at least as an experiment.

LKBU (near Prague), Czech Republic

The old autopilots usually work fine, when driven from a decent navigation source.

In the old days, autopilot certification meant testing in the actual airframe, under various loading, speed, etc, conditions. Well, except STEC which got a lot of STCs on the back of others and without testing, hence their stability is sometimes marginal.

Shoreham EGKA, United Kingdom

I have the Century Autopilot with twin G5’s and it works fantastically. You do need to keep your old Attitude indicator however.

75 % of the time the issues with old Century Autopilots are the plugs /leads as the socket pins open up and make bad connections. Pulling them off, spraying switch cleaner and tweaking the pins will often get the thing working. The rest of the time it is failed Electrolytic capacitors etc

In 5 years or ownership mine has always worked as a wings leveler and my only breakdowns have been MIF (Maintenance Inducted Failures) after annuals etc. Not bad for a 49 year old piece of kit. Last year I decided to get all of the functions working so I send the radio coupler to Straubing for repair, 2 x faulty capacitors were changed and it was calibrated for about Euro 400

There is a very interesting dedicated blog which deals with these Autopilots on

Thanks to @By9468840 for the alternative repair information.

United Kingdom

That’s an amazing site… I hope it stays online.

It’s a fairly typical GA pilot profile: professionally in software, and flies GA as a hobby. And, like the others, he is not putting maintenance manuals online (on an open site) because it upsets people in the industry. Garmin lawyers used to threaten people doing that; not sure they still do but Garmin MMs were never any good for doing actual maintenance anyway.

Shoreham EGKA, United Kingdom

I had a strange phenomena on my Century C41 AP for a while until it was solved a couple of months ago. It brought me last summer in a quite dangerous situation during an ILS approach where I was coupled till minima everything went fine till the last moment. Just before reaching minimums I disconnected the AP the nose went up I felt the whole thing was completely out of trim. Being close to the ground trying to recover by pushing forward with most of my strength with one hand I decided to go around and apply full power, I was loosing speed rapidly. While I was cleaning up the aircraft to assure positive rate of climb the trim started to work again and the loads were back to normal, I used manual trim also to assure it was working correctly. The AP started to misbehave in subsequent flights also when the autotrim light came on from time to time in altitude hold. The manual trim was still working normally. In September I brought the airplane to Avionik Straubing and they checked the computer, which was fine. The culprit was in the pitch trim servo, which was full of dirt and not working smoothly. I can vouch for the professionalism of Avionik Straubing. While the aircraft was in they replaced (on my request) the three coil cords which were a mess in my aircraft from all the switches coming from the yoke, to one beech coil chord with 24 wires to assure that everything runs through one cable. PTT, trim up/down, GA, CWS, AP disconnect etc..Bottom line, I love my C41, its a very good AP even in combination with a KLN90B which a fly ENR in CDI mode of 1NM deflection to assure track guidance. Be aware with autotrim systems failures they can behave like a 737 max :-), without you knowing whats going on. The AP flies the ILS till you disconnect and then whoooooo…..:-). Have your system checked at least once by a professional company knowing these older APs, believe me its worth it…..


I had this about two years ago.
There is a simple test: fly the airplane manually at cruise speed, in trim, and engage AP. Then reduce speed to pattern speed and disengage AP. The airplane should be in trim for the new speed. If not work is to be done.

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