Experts Detail Dangers of Aircraft Proximity After Near Miss

A pilot of a commercial airliner narrowly avoided colliding with four gliders while landing at Luton Airport on April 27, according to a report by the UK Airprox Board. The incident occurred near Leighton Buzzard, Bedfordshire, where the gliders were reportedly operating within or near controlled airspace at the same altitude as the approaching jet.

Such events, known as Airproxes, are defined as situations where the distance, relative positions, and speed of aircraft compromise safety, according to the UK Airprox Board. While the term "near miss" is commonly used, an Airprox is the official designation for an incident that may have jeopardized an aircraft's safety. The distinction lies in the opinion of a pilot or air traffic controller that safety could have been compromised.

While mid-air collisions involving commercial airliners are rare due to overlapping safety systems, the risk is not zero. "Most are assessed as low-risk, and collisions between commercial airliners are extremely rare precisely because of these overlapping safeguards. But the risk is not zero," stated Erika Josefsson, legal strategist and air passenger rights expert at AirHelp. She added that even without a collision, sudden avoidance maneuvers can cause injuries to unbuckled passengers or moving 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 cited the 1978 Pacific Southwest Airlines crash over San Diego and the 2002 Uberlingen collision over Germany, which resulted in 71 fatalities, as examples of system failures studied extensively in aviation safety training. Badra noted that what the public often perceives as near misses are typically "loss of separation" events where safety systems functioned as intended, with each event feeding into safety improvements.

David Martin, managing director at specialist tooling supplier Heamar, explained that "near miss" encompasses incidents with varying levels of risk, with UK classifications ranging from no collision risk to Category A incidents where a serious risk existed. He emphasized that a reported near miss does not automatically imply that disaster was imminent. Martin also highlighted the critical role of the engineering infrastructure, including collision-avoidance and flight-control systems, which rely on aircraft being maintained to exceptionally precise standards.

Generally, an Airprox is considered when the distance between planes is less than 500 feet. However, the Airprox Board clarifies that a report can be filed if a pilot or controller believes safety was or could have been compromised, regardless of the exact distance. In some instances, aircraft miles apart can still constitute an Airprox if required separation standards are not met. The final judgment rests with the pilot and/or controller.

Under typical UK aviation rules, aircraft under air traffic control maintain vertical separation of at least 1,000 feet up to around 41,000 feet. Horizontal separation, aided by surveillance, commonly ranges from three to five nautical miles in high-density airspace. The severity of a loss of separation depends on factors such as direction of travel, altitude, and convergence rate.

In response to potential safety compromises, multiple layers of defense are in place. Air traffic controllers can direct pilots to alter altitude or heading. Additionally, commercial aircraft are equipped with Traffic Collision Avoidance System (TCAS), which operates independently of ground control. If TCAS detects a potential collision threat, it issues pilots with a Resolution Advisory, instructing them to change altitude. This system considers not only distance but also range, altitude, and closure rate to assess the urgency of a developing conflict.