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APU Cannot start in Flight


Pebbles
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We have this aircraft with APU start normally on ground but unable to start in Flight. The APU intake door opened to 15 degrees, rpm goes to 30 percent but no rise in EGT. Failed air test thrice. In the course of fault isolation, we have changed out the no.2 aux touchdown relay, door control relay, door closed control relay, ignition unit, fuel control unit, and APU door actuator. Have anyone out there had this experience and know what is the problems. We have decided to change out the APU. But what if it happen again.

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If the OAT is very low and any moister in the fuel filter/strainer it will freeze and not allow fuel to flow properly. I have had this problem but once we were on the ground, even with ground OAT of 0°C, the fuel will flow and start properly. I had this problem on GTC's also, it would not start right after landing but after about 15 minutes it would start and run properly.

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  • 3 months later...

Hi Neela here,

We had the exactly the same problem. Several flight attempt to start APU if flight fail. We have replace amost all components and even changed the APU in two occasions, but still unable to start in flight.

Ground checks are satis. On ground we are able to start, we even jack up the aircraft, to simulate in-flight condition. APU can start.

Can anybody shed some light on this problem

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