Stec 50 autopilot troubleshooting
The 40/50 apparently only does HDG BUG tracking. The 55X puts the NAV and REV testing into the pre-flight test scripts. Note that even if you have an HSI, you need to set this properly. This is for flying outbound on the front course or inbound on the back course. If you have REV on, it should work backwards. In NAV or APR it should fly towards the needle. You can test it by dialing up a NAV station and turning the OBS/Course Arrow left and right. I think on this unit it only works if also in APR mode. The REV button causes the autopilot to go the opposite way of the needle. The APR button is pretty much the same as NAV except a bit more sensitive (on other STEC units, it allows the GS intercept to happen if an ALT mode is also selected). The KNOB toggles between STB and HDG for each push (provided you have a heading bug hooked up). If you don't, it beeps at you and tells you via the lights which way to trim it. If you have electric trim connected, it will do this itself. While the alt feature pulls on the elevator cables it needs the aircraft to be reasonably trimmed. I sure hope you can find some useful videos on YT, they should help. I would like to try them out one day, in VMC, to see whether I can for example really track the localizer outbound. I have never used the APR or REV buttons. It will fly whatever nav signal you're feeding it (LOC, GPS), check your panel. If the altitude hold mode is engaged, then the autopilot will provide a prompt whenever it is necessary to manually trim the aircraft about the pitch axis using. The NAV mode is enabled by the NAV button (if you didn't guess already). The knob also has a push button which enables the HDG mode. The knob is useful for doing turns with the A/P but I never used it so far. You enable/disable STB mode by pushing the ON/OFF button. IMHO, it is poor wording but I got used to it. It means "stabilize", as in "wing leveler". It will light up one of the trim LEDs if it needs help trimming the elevator.
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It does not use trim but tugs on the elevator cables instead. The 50 model has an altitude hold over the 40 model. My stab at a simple explanation (disclaimer, I am not a CFI): Make sure you can do it in the dark, with your eyes closed, upside down, on fire. There are usually 2-3 ways, learn them all, memorize them.
#STEC 50 AUTOPILOT TROUBLESHOOTING HOW TO#
Of course the first thing to learn is how to disengage the A/P in case it goes bonkers. Or at least read up on it and fly it with another (long-time) owner from the club.
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I agree with the sentiment to get checked out with an instructor.