Area: Hoover Dam
Category: Keep alive
Vehicle type: Either
Goal: Survive as long as you can while health automatically drains
Score for Gold: 0:50.19

Strategy #1:

Destroy everything in sight to get as many health orbs as you can. I've found staying in the hallway where you start works well enough, but you can always leave the base and fight on the Dam highway if you don't like the enclosed space. For some reason the Stealth Chopper tends to work much better for me than the other helicopters I've tried.

Strategy #2:

Make your way out of the base and fly into the room where Megatron was held. There is nothing to attack you, you can destroy the objects in there for energy, then leave and go back in to regenerate them.