This effect is first witnessed at the beginning of
E1L1.MAP: "Hollywood Holocaust" when Duke's vehicle goes down in flames and then explodes. The next (and last) time it is seen is at the beginning of
E3L5.MAP: "Movie Set", when Duke's helicopter crashes and burns. It is extremely easy to do, and looks very cool.
Place either the
DUKECAR (#2491) or the
HELECOPT (#1346) and move it to the exact location and height at which you want it to start. Its angle determines its falling trajectory. You have to give it enough space to complete its fall, otherwise it will hit a wall and slide down until it detonates (which looks very unrealistic). When the game begins, the vehicle will maintain speed and slowly lose altitude until it automatically explodes. All sound effects and other coded effects are automatic.