The main reasons people have crashed Twin Otters at high speed on the ground in the past, have been because they tried to steer them with the tiller too long on take-off, or didn't have the nosewheel centred before putting it on the ground on landing. A 'captain' I knew once, even tried a couple of times to get airbourne with the park brake on.. Didn't lose it, even though the surface was moist, but he did wear a couple of flat spots on the mains when he finally aborted halfway along.. Co-pilot hadn't noticed it still on either..