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Aero Precision provides OEM part support for military aircraft operators across more than 20 aircraft

rpm does not estabilize during starting


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Good day guys.............Tell me!!.....I was going to say change FCU......how can you get this snag with the TD system in null?...................I must have been away from it for too long now!!

The TD valve brake is de-energized engaged. When the brake breaks, it locks the fuel correction in whatever position the TD Amp wants to take it or put it to. After a null adjustment, the adjustment richens or leans the fuel mixture, which the TD Amp tries to correct for it in the controlling range. While the amp corrects, the brake slips a bit, like a clutch, which re-tunes the rich/lean back to where it was before adjustment. I've seen this problem quite a few times. It's actually a fairly common failure mode of the TD Valve due to the nature of the brake being engaged when it is de-energized (broken), but the trim motor still works to attempt corrections.

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TD valves get stuck in TAKE position

I get a lot of those

It's pretty common... That’s why the first thing we do is "adjust" the TD Valve with a mallet....

I've never had to do this but my best engine guy swears you make the TD valve fix itself by making it think it is above 94% (ssc cannon plug off, 94% switch open) and put the throttle in the temp controlling range you can "Make" the TD valve go to full put (with an adjustment, maybe?)

It should work all the inputs would signal an increase in fuel flow....

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  • 1 year later...

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