Dont exactly get what u mean, but I'll try to answer as how I
understand it...
Yes, u can apply for rsaf b4 entering ns. Its possible to go for
your medicals and interviews and stuff b4 going ns, but for
engineering side I'm not very sure.
If he wants to go rsaf just for his ns period, then I doubt
he'll make it. The air force main vocations are all regulars,
meaning people who signed on. U cannot serve ur 2 yr ns as a pilot
or engineering officer. If he intends to jump career like that, its
not gonna work.
For rsaf, they dont really look at the course which u study, but
for engineering, I think that they obviously need an engineering
degree. If your friend intends to sign on as an AEO (Air
Engineering Officer), he can get a sponsorship (not scholarship)
called the Local Study Award (LSA), unless of course his results
are damn good, which u mentioned otherwise. But the criteria is
that he gotta 1st qualify for a place in a local university, which
I suppose limits to only NUS, NTU and SMU. If he intends to go
aussie or some other private uni, I think he gotta pay himself
then.
Any more questions, u can either check the rsaf website or call
up air force recruitment centre @ 1800-2701010.