Username Protected wrote:
A Century III or Altimatic V autopilot will fly an ILS or LPV approach right down to the runway with precision. They simply need a good tuning or minor repairs to do so, if they've been neglected. That tune up will cost a fraction of the cost of a new replacement. And these analog autopilots can be serviced anywhere, in contrast to the new digital autopilots, where any repair is solved with a factory exchanged part. $$$$ and extra down time.
The main reliability issues with the C-III and it's Piper sibling are:
1) Connectors. Edo Aire used a bunch of inline connectors in the harness that tend to lose contact force on the female pin side over time. This often leads to multiple intermittent issues that can be hard to find and fix. Two solutions exist, you can replace some or all of the female connectors with a newer version which has better performance or you can "tweak" the female sockets while they're in the housing with a pick and treat them with some deOxit.
2) The servos use a tiny brushed dc motor and when the brush debris builds up and/or the brushes wear out the servo behavior tends to make the autopilot oscillate in pitch or roll. Having the servos rebuilt at a cost of $1000-2000 is the most common solution.
3) The "Computer" (servo motor drives and filters) has not overcurrent protection so if a servo gets overloaded the output transistors fail (saving the motor). Replacing the transistors and any collaterally damaged components is fairly inexpensive.
4) There are capacitors in the console, computer, and GS adapter which will eventually dry out and lose capacitance. This is tedious work but the replacement capacitors are cheap.
5) An early version of the computer was built with a circuit board that used "griplets" (hollow rivets) to tie traces on each side of the board together and these will inevitably break loose and cause intermittent problems. Replacement computers with a newer board that's made with plated through holes are usually available on the used marked at a reasonable price.
These autopilots are pretty capable, especially when combined with GPSS. What they lack in that case is vertical speed and airspeed modes along with altitude pre-select and of those altitude pre-select & capture is the only one that really reduces the pilot's workload. There's no envelope protection which is more of a safety issue than a workload reducer.
On the plus side, these autopilots are simple enough that they are easy to troubleshoot and repair and full maintenance documentation is readily available.
