A crash landing is an emergency maneuver that is performed when there is insufficient time to land the ship or craft properly, or the vessel lacks the ability to land. Crash landings are often caused when the vessel is sent hurtling into a planets atmosphere either too fast or with no control to the helmsman
In 2371 the USS: Enterprise was forced to crash it's saucer on Viridian III after it was caught in the shockwave of the exploding stardrive section. The helmsman had no control over the crash but the decent of the ship was leveled somewhat by rerouting power to the latteral thrusters. In an alternate timeline Voyager was forced to crash on a class L planet after being thrown out of slipstream, the vessel would have broke up if they did not attempt to land, however the vessel came in to fast and crashed violenty on the plantes surface, destroying one of the nacelles and killing all hands par Harry Kim and Commander Chakotay who were on the Delta Flyer. This timeline was averted by the future Kim when he sent course corrections to Seven of nine which collapsed the slipstream, saving the crew.