Complex sentence: The tail was off the ground and still running on the main wheels, with occasional hops into the air, when the top two engines were started, the aircraft pitched forward burying the nose into the ground seriously injurying all on board.
Split into simpler sentences: The tail was off the ground and still running on the main wheels, with occasional hops into the air, when the top two engines were started. The aircraft pitched forward burying the nose into the ground seriously injurying all on board.