Originally Posted by Arfur Dent
Basically, Mr Hill commenced a looping manoeuvre at too low an altitude to complete it safely.
Can't believe I'm responding to this given the number of similarly uninformed comments.
You can plan to start a vertical manoeuvre well below exit height as long as you have enough energy and that is the basis for many display aerobatics. Conversely looping manoeuvres can have an entry height higher than the exit height. It's all to do with energy management and designing displays.