Why do you start #4 & #5 first?

The sequence is; #4 then #5, then the rest. You could use #3 or #6 to start as
well, I'm guessing they just picked #4 because they needed to pick an inboard
engine and #4 was the closest to the watchful eyes of the Aircraft Commander
(I'm not really sure why they picked #4 out of the 4 they could have?)

You want to use inboard engines because the bleed air manifold connecting to
the outboard engines is only designed to have cooled air blown into it, not hot
air out of it. Basically, if you start #8, then run up #8 to start the rest,
you can over temp the "plumbing" leading from the #8 engine. Same is true for
#1, #2 and #7. On occasions, the manifold for one of the outboard engines will
stick open after the switch has been placed to CLOSED and either during the
anti-ice check, or initial takeoff you'll get a manifold overheat light. The
bad part is, you have no idea which engine and have to go through a little
"trial and error" to figure out which engine is the criminal. On takeoff the
light comes on immediately upon turning the air conditioning on (somewhere
prior to 10,000').



BUFDRVR

"Stay on the bomb run boys, I'm gonna get those bomb doors open if it harelips
everyone on Bear Creek"