If you want to be a bit of a whacker, get a pair of Corcorans. They are the boot US paratroopers jumped in WWII and have been used by Air Cav up until Viet Nam. The leather uppers will protect your foot from debris and other abrasion and they are mighty comfortable once the break in. The leather forms to your foot very nicely
If your looking for the supreme light boot, find a pair of the Viet Nam Jungle boots, they have a totally nylon upper so they are very light and breathe well
Actually, those boots might be ideal, originally designed for tank crews, the straps are designed to replace laces because the laces had a tendency to snag on things inside the tank compartment. The same might hold true inside a helo. Although the tanks in question were Shermans from WWII
I wear Dr. Martens industrial wellingtons. They are comfortable, meet all required ANSI and ASTM standards, have great ankle padding and support, and are easy on and off. In my opinion they are one of the best pairs I have worn on the helo.
Jet A has a flash point of +100*F, so an actual fire is unlikely. Not to mention that 'crashing' is the most likely cause for a fire that involves the crew compartment so I wouldn't worry about the boots being Nylon at this point. If it's just a flash fire, your trouser legs will cover the nylon portion of your boot and a fire that's more serious will have your Face / Neck / Hands melting anyway :unsure:
Wear something comfortable, not too heavy and get good socks.