Background
A NMAC is an incident associated with the operation of an aircraft in which a possibility of a collision occurs as a result of proximity of less than 500 feet to another aircraft, or a report is received from a pilot or flight crew member stating that a collision hazard existed between two or more aircraft. A report does not necessarily involve the violation of regulations or error by the air traffic control system, nor does it necessarily represent an unsafe condition.

Historically, a NMAC was classified as an incident and reports of NMAC events were maintained in the FAA's Incident Data System, together with reports of a variety of other events. By the mid-1980's, NMAC's were considered to be sufficiently important to warrant the establishment of a separate reporting system and investigative procedures. All NMAC reports are thoroughly investigated by FAA inspectors in coordination with air traffic controllers. Data obtained from NMAC reports is used to develop programs, policies and procedures to reduce NMAC occurrences and thereby enhance the safety and efficiency of the air transportation system.

It is the responsibility of pilots and/or flight crew members to determine whether a NMAC actually did occur and, if so, to initiate a NMAC report. There is, however, no regulatory or legal requirement that a pilot and/or flight crew report a NMAC event, although they are encouraged to do so. The fact that pilots and/or crew members initiate NMAC reports raises two important issues for the user of this information. First, to some degree the data likely will be subjective. This necessitates that considerable caution be exercised when evaluating individual NMAC reports. Second, the number of NMAC reports filed probably will not represent the total universe of such events. Therefore, the use of this data to calculate NMAC rates by individual airline is unlikely to result in a metric that is a valid indicator of safety performance.

Using the Database
Things You Should Know
The NMAC reporting system was revised substantially in 1992. Only reports submitted since that revision are available on this Web site. The geographic location of a NMAC is reported in terms of distance (nautical miles) and direction (degrees magnetic) from the nearest air navigation facility, airport or airway fix (VOR, NDB, airport, airway intersection). Those that occur in oceanic airspace are reported by latitude and longitude. Since several air navigation facilities frequently are located adjacent to airports, selection of an airport in the search criteria is unlikely to result in the retrieval of all reports that otherwise could be associated with that airport.

Subjectivity
The data received in a NMAC report represents what the reporter believes he/she saw or experienced. The accuracy of the reporting individual's perception of what occurred can vary considerably among the pilot/flight crew population, depending upon a variety of factors such as pilot/flight crew experience, visibility conditions, proximity of the aircraft involved, relative angle of approach, size of the aircraft involved, the trauma experienced by the pilot or flight crew, etc.

For example, at higher altitudes, in the absence of visual reference points, even the most highly trained and experienced pilots may experience difficulty when reporting such critical information as missed distance, particularly when the NMAC encounter may have lasted only a fraction of a second. While one of the purposes of the subsequent FAA investigation of a NMAC report is to remove as much subjectivity as possible through verification of the information contained in the pilot/crew member report, the investigator's ability to verify this information may be very limited; e.g., if the location of the NMAC event is outside air traffic control radar coverage, precise verification of missed distances is a formidable task.

Under-reporting
The submission of a report of a NMAC event can be influenced by many considerations. Pilot experience and the operational environment they routinely fly in can influence reporting. Pilots that routinely fly in heavily used airspace and are familiar with operating in relatively close proximity to other aircraft may consider an encounter of this type to simply be a part of the operational environment and not something that merits reporting, whereas a pilot that usually flies in sparsely used airspace and is unfamiliar with operating in close proximity to other aircraft may consider the same event to be an extremely serious event that urgently must be reported.

Past reporting trends also suggest that the motivation to report is at least in part influenced by pilot perception that the reporting of NMAC events contributes to aviation safety and therefore is worth the time and effort required to file a report. Following a NMAC event that receives widespread media attention, there is a tendency for the number of reports filed initially to increase, sometimes substantially, and then to decline over time to near previous levels. Fear of a potential FAA penalty or even attitudes that pilots and flight crews hold about governmental institutions can influence a decision whether to file a NMAC report.

Some NMACs, including those which may involve unsafe conditions, may not be reported either because of lack of awareness of the NMAC reporting system or the fact that the flight crew simply did not see the other aircraft due to restricted visibility. The cumulative effect of all these factors that influence the submission of a report is that it is highly unlikely the NMACs reported to the FAA represent the total universe of these events.

Types of Search
Textual search across all data fields is provided. Identifying additional information prior to the search can also narrow the search: Report Number, Start/End Dates, State Code, Aircraft Make/Model, Operator/Airline, Type of Flight Operation and Airport Identifier. In general, keyword searches using just the text search box will not return the same number of records as searches conducted using the additional fields on the query screen. This result is because the text search box searches for all occurrences of a word or string throughout the report, whereas a field on the search form is tied to a single field on the report. The "Help" function on the query screen provides examples of how to structure queries.