Counting fatalities only of those on a flight, the deadliest airplane crash in history occurred on March 27, 1977, when two Boeing 747 passenger jets (KLM flight 4805 and Pan Am flight 1736) collided on the runway at the airport on Tenerife, Canary Islands, Spain. The Tenerife airport disaster, as it became known, resulted in 583 fatalities. The collision was blamed on heavy fog and miscommunication.
Counting fatalities of both those on the flight and the ground, American Airlines flight 11 and United Airlines flight 175 were the deadliest crashes. Both planes were hijacked by terrorists on September 11, 2001, and flown into the World Trade Center in New York City. The attacks caused the deaths of some 2,750 people.