Near Miss Incidents in Aviation: Understanding the Risks and Safeguards

A recent incident where an airliner narrowly missed four gliders while landing at Luton Airport has brought the risks associated with aircraft flying too close together into focus. The UK Airprox Board investigated the April 27 event, noting that the gliders appeared to be operating near or within controlled airspace at the same altitude as the airliner.

While mid-air collisions involving commercial airliners are rare due to overlapping safety systems, the risk is not zero. According to Erika Josefsson, an air passenger rights expert at AirHelp, even without a collision, sudden evasive maneuvers can cause injuries to unbuckled passengers and crew.

Monica Badra, founder and CEO of aviation software company Aero NextGen, described a near miss where aircraft come within a few hundred feet of each other as "extremely serious." She pointed to historical incidents like the 1978 Pacific Southwest Airlines crash over San Diego and the 2002 Uberlingen collision over Germany, which killed 71 people, as examples of system failures. However, Badra also noted that many events reported as near misses are actually "loss of separation events" where safety systems functioned as designed, with each incident feeding into safety improvements.

David Martin, managing director at Heamar, explained that the term "near miss" can encompass incidents with varying levels of risk. In the UK, classifications range from no collision risk to Category A incidents where a serious risk existed. He emphasized the underlying engineering infrastructure, including collision-avoidance and flight-control systems, which rely on aircraft being maintained to precise standards.

An "Airprox" is the official term for a situation where, in the opinion of a pilot or air traffic services personnel, the proximity, relative positions, and speed of aircraft have compromised safety. The UK Airprox Board distinguishes this from the common usage of "near miss." A report can be filed if a pilot or controller believes safety may have been compromised, even if the aircraft are miles apart, provided a required separation standard has not been met. The judgment of whether to file an Airprox rests with the pilot and/or controller.

Generally, aircraft under air traffic control are required to maintain specific separation distances. Vertical separation is typically 1,000 feet up to around 41,000 feet, while horizontal separation can be five nautical miles, reducing to three nautical miles in high-density airspace. The seriousness of a loss of separation depends on factors like direction of travel, altitude, and convergence rate.

When an Airprox is reported, investigations begin with gathering data such as radar recordings, radio transcripts, and pilot/controller statements. Further investigation leads to a comprehensive report assessed by the Airprox Board. Safeguards include air traffic controllers instructing pilots to change altitude or direction. Additionally, commercial aircraft are equipped with Traffic Collision Avoidance System (TCAS), which operates independently of ground control. TCAS can issue pilots a Resolution Advisory to climb or descend if a collision threat is detected, considering factors beyond just distance, such as closure rate, to assess the urgency of a potential conflict.