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 mid-air collision.
Most common reasons for a near miss usually are divided into 3 groups:
— sudden inability of an aircraft to maintain prescribed flight level due to technical malfunctions (such as engine failure, fire on board, 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 prescribed flight level and continues to gain or lose altitude;
— controllers’ error.
Every year about 20 near misses, caused by ATC-related reasons, occur in Russian airspace. 2 to 5 of them are regarded as serious. Usually they have similar scenario: they happen during «slow traffic» period of the working shift, when controllers 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-instructions. When they finally find out that the situation is developing into a conflict, they give wrong or contradictory instructions, which only makes things worse. (For example, the near miss, that happened on 11th of April 2011 in Rostov ATC Center, when Avianova-482 A-320 crew received 4 self-contradictory commands in a row and still lost separation from Antonov-26 military aircraft). Other near misses occur in very busy airspace, but their reasons are different: in such cases pilots usually confirm 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.
Practice shows that work experience doesn’t always play significant role in frequency of controllers’ errors. If an experienced, well-educated person still makes a mistake, it doesn’t mean, that he/she is a bad specialist. It means that there are some hidden reasons in work organization, that are potentially dangerous for flight safety. In general these reasons often are: high workload, inconvenient airspace organization, not user-friendly equipment, lack of assistance from other controllers / shift supervisors, personal problems.
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 prognosis 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 sound alarm rings.
Wietse de Graaf