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S-tec AP problems

2004-09-23 13:56:41

S-tec AP problems

I recently bought a 1977 172 that has a stec AP with altitude hold. The other day It stopped working in flight but continued to hold altitude. It would not track either the vor or the gps. I tried turning it on/off to reset it but no good. On my return trip it work all the way back. Now yesterday it did the same thing. No tracking but held altitude. Any thoughts?

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2004-09-28 14:25:31

Re: S-tec AP problems

My understanding is that S-tec will not engage the altitude unless Hdg or Nav is engaged. If Alt is staying on I would think that HDG or Nav is still engaged but not recieving input from the GPS. Is the CDI properly selected on the GPS and does it do the same thing if you just put it on Hdg?

John

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2004-09-28 23:23:10

Re: S-tec AP problems

Don,
If you already verified that you were in the Heading mode (for GPSS) or Nav mode (for VOR tracking), I would verify that your nav 1/nav 2 toggle is/was properly set. But I hope by now you solved your issue.

Steve

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2004-10-28 01:26:33

Re: S-tec AP problems

Still nothing. I had found out that there is a plug in the wing going to the sro that tends to corode. So I am checking it out.

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2004-11-03 20:36:41

Re: S-tec AP problems

Sounds like your Turn Coordinator to me. The STEC gets a rate signal from the T/C. As long as the Tach portion of the T/C output is good, the unit will engage HDG and NAV mode but if the rate portion is bad it won't track L/R inputs or HDG from the DG. The fact that the HDG mode is engaged allows the unit to engage in ALT mode.
I have seen this a number of times and the Turn Coordinator always solves the problem.