near midair collision

An incident associated with the operation of an aircraft in which a possibility of a collision occurs as a result of a proximity of less than 500 ft (150 m) to another aircraft, or a report is received from a pilot or a flight crewmember stating that a collision hazard existed between two or more aircraft. It is the responsibility of the pilot and/or flight crew to determine whether a near midair collision did actually occur and, if so, to initiate an NMAC report. The report should include the time and the location of the incident and altitude; the identification and type of reporting as well as of other aircraft; the aircrew’s destination; the name and home base of the pilot; the type of flight plans; the station altimeter setting used; the weather conditions at the altitude of the incident; the approximate course of both aircraft and if any of the aircraft was climbing or descending; the reported separation in distance at the first sighting; the proximity at the closest point horizontally and vertically and the length of time in sight prior to evasive action; and the details of evasive action and injuries to personnel, if any. There are various degrees of hazard (NMAC):

i. Critical. A situation in which collision avoidance was due to chance rather than an act on the part of the pilot. Less than 100 ft (30 m) of aircraft separation would be considered critical.

ii. Potential. An incident that would probably have resulted in a collision if either pilot had taken no action. A proximity of less than 500 ft (150 m) would usually be required in this case.

iii. No hazard. A situation in which direction and altitude would have made a midair collision improbable regardless of the evasive action taken.