Xavion!

In flight, Xavion constantly imagines engine-failed glides to every runway in gliding range, and then shows you the safest-possible route as Highway-In-The-Sky to take in the event of engine failure. This, finally, gives you guidance after an engine failure that is based on energy-management all the way down, where the computer does the glide-planning for you you just fly through the hoops to the runway. Continued use of GPS running in the background can dramatically decrease battery life.)