the 1956 grand canyon was a mid-air collision that happened on saturday, 30 june 1956 at 11:31 am mountain standard time. a united airlines plane running as united airlines flight 718 hit another airplane owned by trans world airlines "(twa)", operating as trans world airlines flight 2. the aircraft involved was a douglas dc-7 and a lockheed l-1049 super constellation. the crash happened over the grand canyon within the boundaries of grand canyon national park. all 128 passengers and crew on board both flights died in the collision. the crash was the first commercial airline crash with over 100 deaths, and led to lots of changes in flight control in the united states. the crash site today is considered as a national historic landmark.