Originally Posted by
FlightDetent
HF to consider: Who's gonna recall the correct EGT temp limit for an in-flight restart in the heat of the moment?
Why is it (ehm) that FADEC is not allowed to abort the inflight restart .... so why would you.
It's certainly not clear-cut - especially in an all-engine out situation.
At least on Boeing, EICAS will display the in-flight EGT start limit (and the appropriate start envelope information - including cross-bleed if applicable)(maybe not on a 737 - not sure about that part). The real question is - is it an emergency? If it's an emergency, then by all means use the in-flight start limit and let autostart do its thing. But if you are so high that you're above the in-flight start envelope, I'd argue it's not (yet) an emergency (even all engine out - if you're above 30k - then it's not an emergency although in the heat of the moment you may not be thinking that...).
In a non-emergency situation, using the full in-flight start EGT limit
may result in economic turbine damage, and if you're outside the restart envelope - in a non-emergency - and you damage the turbine trying to start it, you may find yourself having a rather unpleasant conversation with management. I'd like to think that most pilots would know what the ground start EGT limit is for their particular engine/aircraft (although automation - in this case autostart - might interfere with that). In a non-emergency situation, respecting the ground start EGT limit during an in-flight start should preclude doing damage.
The other side of that is that pilots have been known to abort what should have been successful starts - even during an all engine out emergency. Back around 1990, a KLM 747-400 flew through a volcanic ash cloud near Alaska and lost all four engines. They got down to ~10k before they got the engines restarted. Looking at the FDR data after the event, it was determined that the crew had repeatedly aborted what appeared to be successful starts during the emergency (the CF6-80C2 engines on the event aircraft had a very good autostart system - unlike the PW4000 and RB211 autostart systems on the 747-400).
Like I said, it's not always clear cut what to do - particularly in an all engine out situation. But if you trash the turbines trying to restart the engines no matter what, you may find yourself praying you're as good (and lucky) as
Carlos Dardano when he deadsticked TACA 110 onto a dike outside New Orleans...