One the 747-400 (with autostart) and the 747-8 you can start two engines at a time - although if you're at higher altitudes you probably don't want to.

Curious to know what happens when there isn’t enough ‘puff’ to start two engines simultaneously in that scenario


Will the auto start / FADEC abandon the start(s) if adequate rotation is not achieved within a specific time period, close to starter duty cycle limits ?


Assuming it would not allow fuel on in this circumstance ?

That's basically correct - the autostart measures how long it takes of N2 (or N3) to accelerate - if it's too slow it aborts and puts up the ENG X AUTOSTART message on EICAS (and sets a CMC message as to the cause).
Apparently that's happened during single engine starts on the Large Cargo Freighter 747-400 (aka the Dream Lifter). As part of the mod, they removed the APU (running the fuel and pneumatic lines through where the fuselage swings open would have been problematic) so they need a ground cart. Turns out not all ground carts are up to the task...

LEAP
 

My shop is all LEAPS. I think we're up to 75 or so neos now.
The P&W have an extra bus start option I understand, where one engine can be in its start cycle when the other is cranking.
Interestingly, there is no documented limitation on a serial start on the LEAP, and I've been told dual starts are the norm on pre delivery flights. I'd try it in the Sim, but my knuckles are going to be rapped enough...

Thanks for the reply, incidentally does opening the swing tail on the Dream Lifter require any flight control cables to be disconnected?

I don't believe so - the flight control cables and such run through the hinges (one of my work buddies had to the sweat rotor burst for the tightly grouped wiring and flight control cables). The turn times and usage rates for the LCFs (at least pre- pademic) was such that having to physically disconnect and reconnect cables would have been a real problem.

Interesting

Thanks for enlightening