I'm beginning to wonder how many other things they've had in James Bond films aren't as far-fetched as they first appear!
Powerwise, I thought that long pipe from which the saw rail is hanging might be a tube for compressed air, however looking at the company's website, they say it uses a 'compact fuel injected engine'; presumably in that lump at the top of the rail.
Aerial Side-Trimmer Saw - Haverfield
The engine could have an electric start and, like almost every petrol chainsaw, a centrifugal clutch, so, start, throttle and stop would be the only controls needed. As its fuel injected, no choke would be required. If it is a two stroke, it wouldn't mind which way up it is, so could be started before taking off.