Originally Posted by
Matt48
Just a thought, would the crew of QF144 be to start the APU mid flight, about 2hrs out of Auckland, or would it be too cold soaked.
When an engine fails, the checklist directs you to start the APU. It should start. But, in this case, it may have already been running… traditionally for ETOPS/EDTO on the 737 the APU is always left running. So if an engine (or generator) fails, you have an immediate backup. A few years ago, the concept of “APU on demand” AOD came in whereby some aircraft have their APUs monitored for reliability (includes regular start attempts after a long cold soak in cruise at high altitude) and provided they meet all the relevant maintenance criteria they can fly ETOPS with APU turned off.