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With respect to mid-air collisions, how is a near miss calculated, detected, and reported? Does ATC have radar detection, or is it strictly up to pilots to report a close encounter with another aircraft?

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As you wrote in the question body, they're called "near mid-air collision" (or NMAC), not "near miss", if you change the title fast we might avoid the George Carlin references... woops, too late. ;) –  falstro May 1 at 21:03
    
My first thought was to ask the question, why is it called a near miss? I used the term near miss since it seems to be a more common phrase and thought that would be pertinent to the answer. Plus, I want to know about a near miss, not a far miss. –  Magnetoz May 1 at 21:09
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It's called a near miss because the planes came near to each other but missed. It's a miss that was near, not something that was nearly a miss. –  David Richerby May 1 at 23:42
    
At small, busy airports, where most NMACs occur radar is not accurate enough in many cases to judge the situation and it must be done by eye. At large airports or in low visibility the separations are much wider to support radar and therefore NMACs are much less common. –  Tyler Durden May 2 at 15:18
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1 Answer 1

First I'd just like to comment that "near miss" is a bad term (as falstro also noticed). It seems to say that the planes "nearly missed", implying they didn't miss. The FAA uses the terms "Near Midair Collision" (NMAC) for serious incidences, and "loss of separation" for less serious ones. As such, terms like "near miss", "close call", and "narrowly escaped disaster" are not well defined.

ATC does usually have radar. The data is recorded and can be analyzed later. Of course, not all areas have radar coverage. In these cases it is up to pilots to report if they feel safety was compromised. They can use the Aviation Safety Reporting System, which is part of the Aviation Safety Information Analysis and Sharing system.

Especially with commercial flights, Traffic Collision Avoidance System (TCAS) is also used. If TCAS issues a Resolution Advisory (RA), which commands pilots to take action to avoid a collision, the pilots are usually required to report the incident.

A "loss of separation" would be anything less than the required separation.

According the the FAA:

A near midair collision is defined as an incident associated with the operation of an aircraft in which a possibility of collision occurs as a result of proximity of less than 500 feet to another aircraft, or a report is received from a pilot or a flight crew member stating that a collision hazard existed between two or more aircraft.

That and more information about reporting incidents can be found in Section 6 of the AIM.

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