A typical jet turbofan airframe has two engines that each have a generator shaft taking turbine energy and making electrical current. It then has a whole 'nother turbine engine used on the ground and in some other flight legs called the APU; this exhausts out the tail cone usually, and can start engines or provide extra hydraulic power if needed, but is slow to start just like the main engines.

For power loss emergencies, a small spring-loaded fan pops into action super fast, called a Ram Air Turbine or RAT. It can only make enough electrical power to reboot key systems like engine FADECs or avionics, often only on one electrical channel instead of all channels. It's only a turbine, not a thrust-producing fan. It's a pinwheel toy in comparison to the APU and even the APU cannot produce significant thrust.

>It's one of the few segments in IT where you're not directly at constant risk of being replaced by an H1B.

Truth. One of the reasons why I keep gravitating back to defense work. Only since around 2004 or so; there's now this "government shutdown" nonsense, which is a bit of a vicious circle, because programs get fucked over, then you have to roll off the contract and find work on another. And sometimes, there isn't any. (happened to me at Lockheed), so some people have to cycle back into the private sector for a few years (which isn't a bad thing; because THAT is where you pick up new skills, to be honest). Then when some asshole "businessman" crashes the business and does layoffs (to replace you with H1B's), you're back on the street again, and you end up back in the "safe" sector: defense. Oh, and if your Clearance expires while you're in the private sector, then the contractor just pays the $10k (or whatever it is now) to re-do your investigation. This has happened to me twice now.