Executive summary
ATC issues led to a loss of required separation and a near collision between a Cessna 182 parachute-drop aircraft with a single pilot on board and a Bombardier DHC-8 Q311 airliner with 3 crew and 31 passengers on board near Mercer on 9 August 2009.
Both aircraft were operating as cleared by ATC when the airliner’s equipment detected the conflict and directed it away from a potential collision with the parachute-drop aircraft, which had just dispatched 4 parachutists and commenced its descent.
The ATC issues identified were that: the 2-member ATC team managing the airspace did not ensure that a third member of the team was available as required the controller, in clearing the airliner to its destination, did not fully examine the route it was to take and along which a parachuting aircraft was operating the 2 controllers did not recognise the developing conflict as the 2 aircraft approached each other an automated collision warning in the control centre was missed.
During the investigation it was found that an Airways Corporation of New Zealand-sponsored audit had identified that the ATC centre had a rate of communication-related errors higher than those of other comparable control centres, although this type of error was not involved in this incident.
Since the incident, ATC has improved the visibility of the parachute drop area on controllers' screens, and is determining if the activation of the collision warning can be made more distinct. The parachute-drop aircraft has been fitted, beyond requirements, with collision-avoidance equipment similar to that on the airliner.
The Commission has made 5 recommendations to the Director of Civil Aviation to address safety issues relating to the operation and air traffic management of parachute drop areas, ATC's internal standards' monitoring, how the high number of general communication errors was being addressed, and controller actions following collision warning alerts. A sixth recommendation was made to the Director of Civil Aviation, to progress legislation for the acquisition and protection of controller-station recordings to assist future safety investigations.
(Note: this executive summary condenses content to highlight key points to readers and does so in simpler English and with less technical precision than the remainder of the report.)
Related Recommendations
Inquiries into this and previous incidents involving air traffic controllers have relied on radar and radiotelephone recordings, and the statements made by the air traffic controllers. However, verbal communications between controllers in the same work space is critical and integral element of the process for controlling aircraft but are currently not recorded. Without controller-station local area recordings, investigations will not always be able to identify all the contributing factors to an incident or accident and therefore valuable learnings might be lost.
The controllers were unaware of the activation of the STCA, which remained illuminated for about 30 seconds before the 2 aircraft crossed. The STCA is potentially a controller’s last defence for averting a collision and needs to be acknowledged in every case. The lack of response in this incident may indicate that either the STCA activation indications were not effective or controllers had become desensitised to the indications due to a high number of 'nuisance' alerts, or a combination of both.
The Mercer PDA is near a busy international and domestic airport and close to the tracks flown by aircraft flying from Auckland to Tauranga, which alone elevates the risk of midair collisions if air traffic controllers lose awareness of aircraft operating in and around the PDA, or if aircraft deviate outside the PDA.
This incident highlighted a number of individual failures in the system for managing aircraft separation within the Auckland Terminal sector, the busiest sector within the New Zealand air traffic control system. Together with the findings of the NOSS, this indicates that a deeper systemic issue within the overall management of the sector may exist.
The NOSS showed that the number of communication errors by both controllers and pilots, particularly for the Auckland Terminal sector, was unusually high by international standards. This increases the risk of communication errors contributing to a breakdown in safety standards. The Commission believes this is a safety issue that the Director needs to address with Airways and recommends that he satisfies himself that Airways' planned Strategic Safety Plan will reduce communication errors and the consequent risk.
Air traffic control is a highly safety-critical function of the aviation system, yet the process by which Airways ensured that workplace practices were in accordance with documented procedures was not effective, as shown by the non-compliance with written and agreed roster requirements.