The Merion air disaster occurred in southeastern Pennsylvania on April 4, 1991, when a Piper Aerostar propeller-driven aircraft collided in mid-air with a Bell 412 helicopter over Merion Elementary School in Lower Merion Township, a suburb northwest of Philadelphia. All five people in both aircraft were killed, including United States Senator John Heinz, the sole passenger of the Piper. Two schoolchildren on the ground were killed by falling debris. In addition to the seven total fatalities, five more people on the ground were injured.

In aviation, a mid-air collision is an accident in which two or more aircraft come into unplanned contact during flight. Owing to the relatively high velocities involved and the likelihood of subsequent impact with the ground or sea, very severe damage or the total destruction of at least one of the aircraft usually results.