A routine air traffic control proficiency assessment nearly led to catastrophe after the controller "choked" under pressure, leading to four incidents.
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As a result two light planes nearly collided in mid-air while on approach to Hamilton Airport and were forced to take emergency action.
The newly-released report into the 2015 events showed the situation became so critical the assessor was forced to stop and take over as the aerodrome controller.
The Transport Accident Investigation Commission (TAIC) found ''the controller became overwhelmed by the circumstances on the day and lost situational awareness of the aircraft within the control zone".
"Following the fourth incident, the assessor stopped the assessment and took over as the aerodrome controller to resolve the situation,'' the report says.
The Commission engaged a clinical psychologist to analyse the controller's actions. Their assessment found the controller "appears to have experienced 'choking under pressure'."
The impact was defined in the report as causing "a critical deterioration in the execution of habitual processes as a result of elevation in anxiety under perceived pressure, leading to substandard performance".
The Commission also found that the usual briefing procedure before conducting the assessment was not fully followed, and that this "likely affected the team dynamics in the control tower".
The tradition of posting recently qualified controllers with limited experience to Hamilton aerodrome, one of the busiest in the country, was also criticised as it had "the potential to raise the risk profile of the air traffic control unit".
The Commission also found the standard of team resource management in the Hamilton air traffic control tower did not match good industry practice, and some aerodrome controllers are "over-controlling".