I have survived a turn back after an engine failure, but as is stated, it all depends on energy. Interestingly enough, I have practiced it many times and what comes out is not just energy; wind and runway length play a part. If the wind is light and the runway short, if the engine fails at 600 feet, one loses about 500 feet in the turn-back which puts you a long way from the runway. If the runway is long and/or the wind strong, one reached 600 feet even before the end of the runway. Hence one rolls out of the turn-back over the upwind threshold at circa 100 feet. Of note is the angle of bank required; about 45 deg is optimum. But that requires a lot of speed to avoid a stall/spin and thus a very steep nose down attitude. Mind you, though a good wind helps with the turn-back, it will seriously increase your ground speed on landing. If you have a long runway like Kemble, that may be ok. A small grass field like Compton Abbas will be problematic. If conditions are not right or you are relatively inexperienced, landing ahead is the only option. Better than a spin/crash. Sorry, off subject, and mega condolences to the families concerned in this terrible crash.