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Croos over cut TIT


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I think you are asking: Why crossover is 800-840 degrees, and if it is not, why should we correct the problem? Am I correct?

There are several reasons why crossover at 860 degrees or 780 degrees is bad.

1. Throttle alignment. The throttles all have to be within 1/2 knob of each other above crossover when aligning all 4 engine TIT signals. Below crossover, we have no temperature controlling, so we don't care about throttle alignment below crossover.

2. If the TD system is tuned properly, crossover will be 800-840 degrees. If it is not 800-840, your TD system is improperly tuned or you have a bad coordinator.

3. If the TD system is tuned properly, and the coordinator is not malfunctioning, then it could be a sign of TIT indicator malfunction, which should be repaired immediately.

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As long as the TIT corrects to 800-840 at light-out, there is no problem: it merely

indicates the FCU to be rich or lean at that point. A good run with several NULL starts

and a rich/lean check will tell you whether there is a problem or not with the FCU fuel

scheduling.

Performance is not affected by a high or low before-light-out TIT. If the corrected TIT

is only 780, it is probably indicating a broken or misrigged coordinator (a good place to

start when dealing with TD problems)

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