Near miss is a special aviation term, describing loss of safe longitudinal, vertical, lateral or time separation between aircraft during the flight. In worst cases near miss can develop into a mid-air collision.
Most common reasons for a near miss usually are divided into 3 groups:
- Sudden inability of an aircraft to maintain its designated flight level due to technical malfunctions (such as engine failure, fire onboard, decompression) or due to hazardous (unfavorable) weather conditions (most likely thunderstorm, severe turbulence, severe icing);
- Pilots’ error. When the crew is distracted from controlling their climb or descent, level-bust can occur. In such cases the aircraft doesn’t stop at the assigned flight level and continues to gain or lose altitude;
- Controllers’ error. Due to fatigue or excessive workload controllers sometimes lose some of their sharp attention and quick reaction; suddenly they receive request from one of the crews for a level-change, and they give such clearance without making sure that this maneuver would be safe. They don’t consider other aircraft as a potential danger, don’t make any calculations, don’t supply the crew with traffic information and appropriate rate of climb or descent instruction.
Other near miss scenarios can occur in very busy airspace but their reasons are different: in such cases pilots usually confirm the wrong flight level to reach, but controllers are too busy or too tired to detect and fix the mistake. Some controllers also think they are saying one flight level, when in fact they are saying different numbers.
Modern ATC equipment helps controllers in forecasting conflicts between aircraft. These ground-based computers analyze movement of all visible in radar-coverage aircraft and make predictions of their maneuvers. Once computer detects potential conflict, appropriate labels on controllers’ radar screens change colors from white to orange in order to attract attention. If separation between aircraft gets violated, labels turn red and an alarm rings.