What happened
On 9 August 2009, a potential mid-air collision occurred in the airspace near Mercer involving two aircraft. The first was a Cessna 182 engaged in a parachute-drop operation, which had just released four skydivers and begun its descent. The second was a Bombardier DHC-8 Q311 airliner, carrying 31 passengers and 3 crew members.
While both aircraft were following their assigned air traffic control (ATC) clearances, the airliner's onboard equipment detected an impending conflict. The crew of the Bombardier DHC-8 Q311 took corrective action by maneuvering the aircraft away from the path of the Cessna 182, successfully avoiding a collision.
The investigation
The investigation focused on the performance of the air traffic management team and the functionality of the control center's alert systems. Investigators determined that the two-person ATC team managing the sector was operating without the required third team member. Furthermore, the controller responsible for clearing the airliner to its destination failed to adequately review the flight path, which intersected with the active parachute-drop zone.
Crucially, the investigation established that the controllers failed to identify the converging flight paths as the aircraft approached one another. Additionally, an automated collision warning triggered within the control center went unnoticed by the staff on duty.
Findings
Several systemic and operational failures contributed to the incident:
- The ATC center was operating with insufficient staffing, lacking the mandated third controller.
- The controller did not perform a thorough examination of the airliner's route relative to the parachute-drop area.
- The controllers failed to recognize the developing conflict between the two aircraft.
- An automated collision alert in the control center was missed by the personnel.
- An audit had previously noted that this specific ATC center experienced a higher rate of communication-related errors compared to similar facilities.
Safety action
Following the incident, several measures were implemented to enhance safety. ATC has increased the visibility of parachute-drop zones on controller radar screens and is evaluating ways to make collision warnings more distinct. The Cessna 182 has also been upgraded with collision-avoidance technology exceeding standard requirements.
Additionally, the Commission issued six recommendations to the Director of Civil Aviation. These address the management of parachute-drop areas, the monitoring of ATC internal standards, the mitigation of communication errors, and the protocols for responding to collision alerts. A final recommendation focused on advancing legislation to ensure the preservation of controller-station recordings for future accident investigations.