Mid-air Collision
Two aircraft collide in flight. Investigations centre on separation: who was responsible for it, what each crew could see, and what the collision-avoidance systems did.
A mid-air is a failure of separation, and separation is a shared responsibility between air traffic control, the crews' own lookout, and the traffic alert and collision avoidance system. A report will normally reconstruct all three.
Note the distinction the archive draws: a collision between two aircraft on a runway or taxiway is a ground collision, not a mid-air. Case files involving two or more aircraft are labelled "Multi-aircraft" unless the collision genuinely happened in flight.
Related terms
Airborne collision avoidance. It interrogates nearby transponders and, if a collision is likely, issues a coordinated climb or descend instruction to both crews.
An airworthy aircraft, under the crew's control, is flown into ground, water or an obstacle — usually because nobody on the flight deck knew the terrain was there.
Decisions and pressures outside the flight deck — dispatch, loading, scheduling, air traffic services, company culture — that shaped the outcome.