Hi there!
I have a 1985 Turbo Saratoga SP with a KFC 150 autopilot system, coupled to the GNS430.
The trouble is flying in level flight, the autopilot with ALT mode engaged would always chase the altitude. The deviation of the desired altitude is approximately 100 ft to either side. The deviation used to be around 300 ft before troubleshooting started.
Climbing or descending in the pitch mode, i.e. operating the rocker switch, is quite fine. The airplane can hold it's attitude on the way up or down.
Trouble shooting started by taking the horizon apart. As the engineers pointed out there is a contact ring, similar to a rheostat, which is often corroded, therefore sending the flight director all over the place.
After this repair has not cured the problem the pitch servo was examined and overhauled cause the motor seemed to be very weak. With the servo reinstalled it's still a bit at the lower limit of strength.
A parallel way of troubleshooting was to pull off the static line from the back of the autopilot computer to let the computer "breathe" ambient air in the cabin. There was no difference.
Next step will be to replace the pitch servo by a new unit.
Has anybody experience with this kind of problem?
Rgds Tom
I have a 1985 Turbo Saratoga SP with a KFC 150 autopilot system, coupled to the GNS430.
The trouble is flying in level flight, the autopilot with ALT mode engaged would always chase the altitude. The deviation of the desired altitude is approximately 100 ft to either side. The deviation used to be around 300 ft before troubleshooting started.
Climbing or descending in the pitch mode, i.e. operating the rocker switch, is quite fine. The airplane can hold it's attitude on the way up or down.
Trouble shooting started by taking the horizon apart. As the engineers pointed out there is a contact ring, similar to a rheostat, which is often corroded, therefore sending the flight director all over the place.
After this repair has not cured the problem the pitch servo was examined and overhauled cause the motor seemed to be very weak. With the servo reinstalled it's still a bit at the lower limit of strength.
A parallel way of troubleshooting was to pull off the static line from the back of the autopilot computer to let the computer "breathe" ambient air in the cabin. There was no difference.
Next step will be to replace the pitch servo by a new unit.
Has anybody experience with this kind of problem?
Rgds Tom
