Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Communication Breakdown
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Human Factors; Aircraft; MEL; Procedure
In ZZZ we attempted to start number two engine using APU air and it spooled up abnormally slowly; and I noticed that the EGT seemed to lag. At 45% N2 the start stagnated and decayed until a 2.5% N2 decrease and Engine Fail indication on the ECAM. We stopped the start; then following guidance in our paperwork; we started number one (which also stagnated a little bit but then started normally) and then attempted a second start on number two using cross-bleed from the number one engine. We allowed the engine to spool up to 25.7% N2; then added fuel. At starter cutout; the engine hung again; dropping to about 43.2% N2 and hanging there before slowly spooling up to about 43.8% N2 when it timed out for the start and Engine Fail was indicated on ECAM again. Our Quick Reference Handbook said we could attempt a second start after the first hung start; but that maintenance action was required if the second start failed. At that point we requested a tug and BTB to our parking space. This is where Maintenance Control got involved. At first they suggested that we defer the APU bleed; however it was obvious to me that the air was not the problem (we used a separate source for each start); so I told him the APU bleed deferral was not sufficient. Then he suggested that a problem with the Integrated Drive Generator might be causing the hung start and suggested we defer that; and I agreed it could be tried. As part of the maintenance action during start the Inetgrated Drive Generator was disconnected and deferred; and the Airworthiness Release in the log book was signed off; then we continued getting the jet started and were on our way. During the flight the APU was running as required by the deferral; and at 36;000 ft. it automatically shut down. I attempted to start the APU; and on the second try; it started. I requested and descended to a lower altitude of 30;000 ft. and the APU operated normally for the rest of the flight. If I had not been able to start it; I would have had to advise ATC and divert. I wrote up the APU under a P code for momentary or transitory malfunction. In ZZZ1; maintenance checked the APU for any failure codes; did the repetitive inspection for oil quantity for the Integrated Drive Generator deferral; and signed off the APU. The FO (First Officer) and I discussed the situation and agreed that the APU was not malfunctioning and may have had a momentary problem with operating at high altitude. We accepted the jet for the leg to ZZZ2. With a fresh Airworthiness Release in the log book; we started the number one engine first; then started number two using cross-bleed at the request of maintenance. The number two engine came close to exceeding time limits; but did eventually spool up. We were filed for 33;000 ft.; and at that altitude the APU did the same thing--it shut down--and we were able to get it started again on the second try. We requested and descended to 29;000 ft. for the remainder of the flight. Again; the APU operated normally from there on; and again; I wrote it up with a P code for the shut down. I also made a comment in the logbook about the number two engine start; even though our flight paperwork said that comments for a successful start were not needed. There I made a note that the EGT from fuel introduction to the point where the start stagnated; then started to spool up; seemed abnormally low and was at least 50 degrees cooler at 45% N2 than the other engine. The stagnated start was evident from fuel introduction until after started cutout when it became apparent that the engine was not ready to continue the start on its own. The Integrated Drive Generator has nothing to do with the EGT during start. I suspect something else is going on here; perhaps a Electronic Engine Control problem with the fuel mixture at high altitude; or a sensor malfunction. On further reflection; I feel that the deferral of the Integrated Drive Generator was inappropriate for the problem we had; and I should not have accepted it. It created a problem where we could have been forced to request priority handling and divert. It is likely that whatever is wrong with our engine starts does not pose a safety of flight risk once we get the engine going; so it makes no sense to do a deferral that could compromise safety. Until this is figured out; the guidance needs to be specific and it needs to go out to everyone in the maintenance and crew pipelines and it should be operations friendly. My recommendation is that everything in the fuel system be checked in case it is causing the starting problem for cold engines at high altitude. I think that the bleed system is less likely to be the issue because of the low EGT I saw during all four start attempts on that engine. I also recommend that maintenance be able to attempt at least one more start before the aircraft is taken out of service; and that crew get more guidance concerning the problem. 'Maintenance action' is not enough to let a Captain know what to expect or what to accept. I also have felt for a long time that our systems manual has been scrubbed of a lot of detail about systems with which we do not directly interact; so we are less able to make informed decisions and instead have to rely on experience. That will not always save us from making the wrong call. Everyone in this situation acted in good faith; and I am not writing this report to cast any doubt on anyone. I only want to point out a safety issue that we can avoid in the future.
Pilot reported application of the wrong MEL complicated the flights unnecessarily.