Alright, so since I feel like we're all stumbling our way through the dark so far so here's what I got for ya's so far, because this game is kinda infuriating without having at least a little background.
It appears that all planes, at least that I've found, have two-shots worth of survivability; first time you're hit, you start spazzing out, second time you blow up. When you're spazzing, or if you're parachuting, or on the ground, you're a one-shot-wonder.
You do NOT have to be damaged/spazzing to eject, and you can eject yourself into any other enemy airplane (and... I'm wondering if there's any tricks here, like secret stuff you can hijack) at any time. All you have to do is eject, and have your character hit/land on the plane and you'll have a new ride. These other planes have different characteristics, weapons, etc. When you first eject you don't deploy your chute right away; so you can hop from plane to plane with impunity without losing lives or chutes. This is pretty much the key game mechanic that might not be obvious on the first play or fifty, but I bet it was pretty clear somewhere on the bezel or something! I really like the depth this adds; if you're damaged, do you risk trying to get close to steal an enemy plane, or do you just go ahead and use the chute?
Always be ready to jump when you hit the ground with your chute btw. End of levels; there's a platform that it appears you just have to 'land on' by crashing into it (at least that's what I did, maybe you can eject onto it too) but there's enemies firing at you from it. Arrows will point you to it, and you get a point-bonus at the level end for how many kills you got.
Blammo! 182000
EDIT
Okay, so if you guys will notice, each level is more or less divided into waves of certain types of enemies. If you 'clear' a wave, you get a 20k bonus and an extra parachute. I think I've finally figured out how this game is supposed to work!! I still get spanked by those UFOs tho