Where he'd work afterwards could be limited. He'd have to live in close proximity to an Airport or Aircraft Repair Facility. IF he could get lucky and land a spot with Boeing, he'd be in good shape but that is a TOOOUGH nut to crack. Airlines are constantly laying off etc etc. HVAC??? He could decide to live in Cooter Missouri and HVAC Services will be needed. It's also one of those Trades where he could do lots of side jobs.
I told him when he is at Tech School, do MUCH more than know enough to pass the next test. REALLY dive into it all. Know what every tool is, what it does, what makes that tool or gauge work. To be honest, when I went through USAF Fire School, I did GREAT at the practical training and tests. I wish I had studied BEYOND the Lesson Plans.