Two Dash-8 passenger aircraft avoided collision on approach to Wellington Airport (saved by human and last-defence automated systems) after one Dash-8 followed the wrong lead aircraft. Nobody hurt, no damage. All safety issues addressed, so no new recommendations
Executive summary
What happened
On 12 March 2019, three aeroplanes on scheduled passenger flights were sequenced to land on Runway 34 at Wellington International Airport. The first aeroplane in the sequence, an Airbus A320, was approaching from the south-west. The other two aeroplanes, both Bombardier DHC-8-311s (Dash-8s), were joining from the north-east.
When the first Dash-8 aeroplane (callsign LINK235) was parallel with the runway, the flight crew requested approval for a visual approach, rather than a full instrument procedure. This was approved and the aeroplane continued downwind to position behind the A320.
The second Dash-8 (callsign LINK285), following about two minutes behind the first, also requested a visual approach. This was approved to follow the first Dash-8. However, the second Dash-8 identified the A320 as the Dash-8, then turned towards the runway to position behind the A320. This put it into a conflicting flight path with the first Dash-8.
As the two Dash-8s approached each other, the air traffic controllers were alerted to a potential conflict by an automatic short-term conflict alert warning presented on their radar displays. The approach controller tried to resolve the conflict but could not contact the second Dash-8. They then contacted the Wellington tower controller. The Wellington tower controller broadcast a message to resolve the conflict. At about the same time the respective Dash-8 flight crews saw each other, and both took evasive action to ensure adequate separation was maintained. While taking this evasive action, the flight crews of both Dash-8s received automatically generated, traffic-collision-avoidance alert messages from their onboard systems that advised them to take evasive action to avoid conflict.
Both Dash-8 flight crews avoided the potential conflict and all three aeroplanes landed without further incident.
Why it happened
The Transport Accident Investigation Commission (Commission) found that the crew of LINK285 mistakenly identified another aeroplane in the sequence to land for the preceding aeroplane they had been instructed to follow. The Commission found that the flight crew had insufficient situational awareness in relation to their position in the circuit pattern before they took on the responsibility of maintaining their visual separation from the aeroplane ahead. The lighting and visual conditions prevailing at the time made it more difficult for the LINK285 flight crew to visually identify the preceding aeroplane, and they had not used other means they had available to validate their visual interpretation.
In addition, the Commission found that the automatic and human defences incorporated into the air traffic control and aircraft systems detected the potential conflict and prevented the situation escalating.
The Commission found three safety issues. Two safety issues were related to the situation where a flight operating under instrument flight rules changed to make a visual approach to land. The first of these was that critical information for a flight crew to conduct a visual approach was not required to be passed on to the flight crew. The second was that air traffic control procedures could create a situation where an approach controller would be unable to contact a flight crew when the controller was still responsible for monitoring that flight crew’s compliance with an instruction. A third safety issue was that, after a serious incident, the operator’s current practice allowed potentially critical evidence contained in two separate aircraft cockpit voice recorders to be lost.
The Commission considered that the actions taken by the respective operators adequately addressed these safety issues, so has not made any safety recommendations.
What we can learn
The visual identification of other aircraft can be challenging. Pilots should use all available resources to build situational awareness.
When a controller issues a clearance, it is important to monitor the flight crew’s initial compliance to check it has been interpreted as intended.
Traffic Collision Avoidance System equipment is an effective defence against mid-air collisions, and its display is also a useful instrument that flight crew can use for their situational awareness.
Who may benefit
Commercial pilots, air service operators, air traffic service providers and air traffic controllers will benefit from this report.