Is the real NG's APU really powerful enough to start both engines at the same time?Let's assume a normal day (ISA, density altitude at say 500 ft AGL)Mark

Never tried to motoring both engines at the same time... not sure if APU is able to provide sufficient air, unfortunately I cannot try anymore, but, if I will have the luck to work on a 737 (either classic or NG), I will just give it a try (only dry motoring). If this will get too time, it will be a risk for engine acceleration after light up, so hung or hot starts are possible.In the NGX I often start the second engine as soon I give fuel to the first one, without waiting for starter cutout.

What's a fuel pomp?

Well, that depends on the "circumstance". :(

Fuel pumps: not bug.But the NGX shouldn't be able to start 2 engines at the same time. This is might be bug?

I don't think being able to start both engines together is a bug. It's most unlikely there is sufficient bleed air capacity to safely start one engine but not enough to turn two. Maybe the two starts should be slower and hotter, but it's quite likely the engines could well start safely. It may not be correct Boeing procedure but this does not mean it can't be done. Too many add ons are designed around published procedures and checklists. It's good that PMDG does not do this. A double engine start may or may not be possible, but programming to make it impossible would be wrong unless this is known to be correct.

 

I don't think being able to start both engines together is a bug. It's most unlikely there is sufficient bleed air capacity to safely start one engine but not enough to turn two. Maybe the two starts should be slower and hotter, but it's quite likely the engines could well start safely. It may not be correct Boeing procedure but this does not mean it can't be done. Too many add ons are designed around published procedures and checklists. It's good that PMDG does not do this. A double engine start may or may not be possible, but programming to make it impossible would be wrong unless this is known to be correct.

Fair enough!

There isn't enough bleed air pressure to start both engines at the same time. And you should wait more than 10 seconds and less than 2 minutes to start the other engine. I use this time to close the isolation valve and turn the Pack 2 on. Of course you have to start engine 2 first to do that.

Well, that depends on the "circumstance". :(

Buh dum dum tsshhh.

There isn't enough bleed air pressure to start both engines at the same time. And you should wait more than 10 seconds and less than 2 minutes to start the other engine. I use this time to close the isolation valve and turn the Pack 2 on. Of course you have to start engine 2 first to do that.

There is no need to wait 10 seconds from a start to another.First of all, the starter disengages before engine is completely stable, so normally, you may wait until engine stabilizes, (this can take a bit more than 10 secs), but, as soon as the starter valve closes, the bleed could be used to immediately start the other engine.Also the 2 minutes are only a "company rule" as the system will be not damaged by the use of the single engine. Just going by memory, I cannot see the EGT rise too much with the engine start, so it should use less air tha a conditioning pack. If the remaining air is sufficient or not, I never tried, but cannot exclude this possibility. I'll check my manuals to see if there are values for air consuption for the starter VS bleed air flow GPM