Topic-icon ATA 73-21, Ground/Flight Idle Control

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4 months 1 week ago - 4 months 1 week ago #716 by Mark D Francis
Another case of an intermittent relay on 767's.

Please reference http://rotate.aero/forum/ata24-767/314-ata-24-33-stby-power-failure-indication for a previous example.


Intermittent flight/ground idle control relay.

When the engine was run previously, N2 speed would jump from the mid-60's to 78% and then back down again.There was no defined time sequence for this failure. Engine bleed or electrical loads configurations also had no effect on the engine going to flight idle.

When this relay (K434, Flt/Gnd control relay) was removed and powered separately, it would cycle on/off.

This relay is energized on the ground. Failure rates of constantly energized relays seem to be higher than those that are not on the majority of time.




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Last edit: 4 months 1 week ago by Mark D Francis.

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3 months 3 weeks ago #718 by Thomas Richter
Easier than chasing down a wiring issue! Out of curiosity, how old are these relays ?

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3 months 3 weeks ago #719 by Mark D Francis
As they age, they sometimes get pitted and rough on the case. This can come from a combination of external heat, cold, or moisture. Sometimes the internal heat generated by the relay coil itself can add to the external case aging.

If I find a pitted case, I'm looking at a decade or older relay. This doesn't necessarily mean it's bad...... just old.

The relay in question above was not that old.

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