B757-200
Flight Crew Air Transport Pilot (ATP)
Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance
General None Reported / Taken
Procedure; Aircraft
We found on our flight plan that morning notes from Dispatch indicating fuel added to accommodate running the APU the entire flight. The reason was; a new APU was installed and an inflight start of that APU was required. They needed at least 2 hours cool down period prior to in flight start attempt. Since we did not have 2 hours to cool down the APU prior to entering ETOPS; maintenance requested that we keep the APU running until 2 hours prior to our top of descent. At that point we were to shut down the APU for 2 hours then attempt the restart at altitude. I shut down the APU as instructed; 2 hours prior to estimated TOD. I then attempted the restart at altitude FL390 after 2 hours cool down. The restart attempt was not successful. EGT raised normally and began reducing as usual but was followed by an APU Fault. Subsequent attempt during descent below FL350 was not successful as well. I then entered my full report of the scenario in the Maintenance Log Book. During the preflight phase of our flight we received multiple ACARS messages from dispatch confirming the procedure to follow which we confirmed. Additionally; during the APU shutdown period; we received an ACARS message from Dispatch asking if we had made our maintenance log entry. I responded by telling Dispatch that we were in the middle of the procedure and would report the results in the maintenance log. Dispatch responded with a thank you.Do not attempt a procedure like this while operating under ETOPS rules again. Domestic flight would have been a better choice for this kind of required check.
[Report narrative contained no additional information].
B757-200 flight crew on an ETOPS overwater flight reported they were tasked with testing the APU with an inflight start; and the APU would not restart. Reporter recommended they do these kind of tests on domestic flights.