Originally Posted by
Musician
So, once the RAT is providing some electrical power and hydraulics, the APU auto-start sequence begins with the opening of the air inlet?
Not specifically familiar with the 787 APU, but I suspect the APU auto-start would commence at the same time as the RAT deployed.
The 787 APU has a dedicated battery, so there is no reason to wait until the RAT is 'on-line' to commence the start sequence.