midair

A midair is a collision between aircraft in flight, typically at altitude where neither vehicle is under ground control or visual oversight of a tower. The term distinguishes these accidents from runway incidents, ground strikes, or controlled-flight-into-terrain events. Midairs remain among the most catastrophic aviation accidents because both aircraft are usually traveling at cruise speed with no time for emergency descent or evasive maneuvering.

Most midairs occur in controlled airspace where traffic separation is supposed to be managed by air traffic control. The classic scenario involves two aircraft on intersecting flight paths at the same or converging altitudes. Commercial midairs are extremely rare in developed nations thanks to radar surveillance, Mode C transponders, and traffic collision avoidance system (TCAS) mandates on large aircraft. General aviation midairs remain more common because many smaller aircraft operate without transponders or TCAS in uncontrolled airspace.

Investigation and prevention

When a midair occurs, recovery of wreckage is distributed over a wide area, complicating investigation. The NTSB focuses on determining whether separation standards were violated, whether pilots maintained proper lookout, and whether ground control failures contributed. In maintenance, the term appears in accident reports and in the procedures pilots use during training for terrain avoidance and traffic awareness.

TCAS II systems are now mandated on commercial aircraft and large business jets specifically to prevent midairs by alerting pilots to nearby traffic and issuing resolution advisories. These systems track radar returns and pressure altitude reports from other aircraft and calculate collision risk. Pilots are trained to follow TCAS guidance even if it conflicts with ATC instructions, making this automated system the last practical defense against midair collision at altitude.