It is standard procedure to auto
-start two engines, at the same time, on the B747-400 in my airline, provided you are below 6,000 ft AMSL and the OAT is below +30°C.
Usually 3 & 4 are started together first, and then 1 & 2. All four engines must be running before the aircraft moves under its own power, delayed starts during taxy-out are not allowed.
The auto-start system monitors automatically all the parameters that B747-100 crews monitored manually, as well as introducing the fuel at the correct point in the start cycle.
It deals with hot starts, hung starts, failed starts, starter motor failures and will abort the start if necessary, and try a re-start, using the other ignitors if required.
It does this flawlessly, two engines at a time, just about every time.
However, if the auto-start system is not working, or if a manual start is required as at MEX
, then we only start one engine at a time, normally 4-1-2-3, and have to monitor, time and control all aspects of the start cycle ourselves.