ANZ DH8C and ANZ DH8C at Wellington on Mar 12th 2019, loss of separation on visual approach, one DH8C followed the wrong aircraft

Last Update: April 14, 2022 / 14:00:28 GMT/Zulu time

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Incident Facts

Date of incident
Mar 12, 2019

Classification
Report

Flight number
NZ-285

Departure
Gisborne, New Zealand

Destination
Wellington, New Zealand

Aircraft Registration
ZK-NEF

Aircraft Type
De Havilland Dash 8 (300)

ICAO Type Designator
DH8C

An ANZ Air New Zealand Dash 8-300, registration ZK-NEF performing flight NZ-285 from Gisborne to Wellington (New Zealand), was on approach to Wellington's runway 34, the aircraft had initially followed instrument procedures and subsequently was cleared for the visual approach to runway 34 and to follow another ANZ Dash 8-300 about 2 minutes ahead of them, that was following another Jetstar A320. The crew however misidentified the A320 as their preceeding aircraft and in following the A320 turned base and final too early.

Another ANZ Dash 8-300, registration ZK-NEH performing flight NZ-235 from Rotorua to Wellington (New Zealand), had requested and was cleared for a visual approach to runway 34 and had turned final behind the A320, when the controller received a short term conflict alert and both crews of the Dash 8 received TCAS resolution advisory, NZ-285 to climb and NZ-235 to descend. Both crews followed the TCAS RAs, the conflict was resolved.

Tower attempted to resolve the developing conflict but could not reach NZ-285 and informed approach, who broadcast according instructions to resolve the conflict, however, TCAS was already issuing the advisories.

Both aircraft subsequently continued for safe landings on Wellington's runway 34.

On Apr 14th 2022 New Zealand's TAIC released their final report concluding the probable causes of the serious incident were:

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 TAIC analysed why the crew misidentified their preceding aircraft:

The flight crew of LINK285 mistakenly visually identified an A320 on its final approach as a Dash-8 on the base leg. This may seem improbable given that the A320 is a lowwing, twin-engine jet aeroplane, while a Dash-8 is a high wing, T-tail, twin-engine turboprop aeroplane. The flight crew were experienced pilots attempting to identify an aeroplane that was the same as the one they were flying and operated by the same company. They were also familiar where aircraft would be on each leg of the approach pattern into Wellington Airport.

...

Workload:

The weather was fine and the flight crew were not dealing with any sort of emergency situation or system failure. There were only two other aircraft in the approach traffic. The cockpit was reported by the flight crew to have been ‘sterile’ with no distractions. This situation would have been unlikely to present a high workload for experienced pilots.

Fatigue: Both pilots in LINK285 had had adequate rest since their previous duty time and said they were alert and focused on the tasks at hand.

Familiarity: The flight crew stated they had briefed for the approach at the top of the descent and were both expecting a standard instrument terminal-arrival route through the waypoints to Runway 34. Although they had not briefed for a visual approach that could deviate from the IFR route, they had both flown visual approaches to Wellington along this route before.

Weather: The weather was fine with scattered cloud clearing from the south of Wellington. The visual clearance from cloud was assured and the horizontal visibility distance was suitable for visual flight conditions.

Pilot interactions:

The captain and first officer both said they worked well as a team.

Neither pilot expressed any concern about their working relationship in the cockpit.

Situational awareness:

LINK285 was on a planned IFR descent profile31 under the control of the approach controller. The approach controller was, at that time, responsible for ensuring appropriate separation from other aircraft, but the flight crew were about to transition to a visual approach.

The flight crew needed to update their awareness of other aircraft in the approach pattern in preparation for conducting a visual approach. A pilot gains situational awareness by their perception and interpretation of the information they receive through their senses. This includes from visually scanning outside, scanning the flight instruments and listening to radio chatter. Where an aircraft has two pilots, they share the workload and confer on their respective observations. This helps them to build a shared picture of other aircraft in the airspace around them.

The flight crew of LINK285 said, during an interview, that they were listening to the Wellington approach frequency and heard instructions being issued to LINK235 and JST290. This indicated that there were at least two preceding aircraft in the approach sequence before they went visual.

According to the ICAO procedures for an IFR flight, to make a visual approach the pilot needs to positively identify aircraft they have been instructed to follow and the controller needs to monitor the pilot’s actions. The guidance for controllers is stated in MATS33 as: After clearing an aircraft for a visual approach and to follow another aircraft visually, radar controllers should continue to monitor the aircraft in order to confirm that the correct aircraft is being followed.

At 1730:45, two minutes before the TCAS-RA, the radar display for the Wellington approach showed LINK235 approximately 8 nm ahead and slightly to the left of the track of LINK285, while JST290 was approximately 9 nm ahead and slightly to the right of the track of LINK285.

The flight crew were required to identify the aeroplane ahead that was just turning onto base. JST290 was on its final approach at the time. The flight crew of LINK285 and the approach controller were both confident that LINK235 had been correctly identified as the aircraft ahead. The approach controller then switched their attention to another aircraft arriving at Wellington on the other side of their screen.

While the relative positions of aircraft on the radar screen were clear to the approach controller, the pilots in LINK285 did not have the same perspective.

At 1730:45, when the LINK285 flight crew stated they had LINK235 in sight ahead, the sun was approximately 24° above the horizon and to their right. The pilot flying recalled that conditions were suitable for a visual approach. There was some cloud around but the sun was low in the sky and it was clearer of cloud to the south. The pilot monitoring had noted that colour clarity was poor.

At that time LINK235 was approximately 6 nm ahead, 2,800 feet below and flying directly away from LINK285. It would have presented as a small crosssectional area with little to no sun reflection and have had very little contrast or relative movement against the background. It would have been difficult for the flight crew of LINK285 to see and visually identify the other Dash-8.

Conversely, JST290 was about the same distance away from LINK285 but lower down and slightly to its right-hand side and flying towards it. The sun would likely have been highlighting the upper surfaces of JST290 against the contrasting darker sea, making its relative movement more obvious.

At 6 nm a pilot would be challenged to distinguish another aircraft’s details and colour scheme. The human eye could detect an object’s movement and distinguish that it was an aircraft at that distance, but the visual acuity of details may not be as clear.

The image derived by a human eye may seem convincing and true to the eye’s owner, but the human eye is well known to have imperfections and be subject to illusionary effects at times.

In the book, Fundamentals of Aerospace Medicine (Davis, Johnson, Stepanek, & Fogarty, 2008), the visual function of the eye is described as: The visual apparatus, stimulated by light, must primarily perform three basic functions. It must be able to perceive an object by the detection of light emitted or reflected from it; this is known as light discrimination. Second, it must be able to perceive the details of an object; this is known as visual acuity. Third, it must allow one to judge distances from objects and to perceive movement in the field of vision. These latter two functions combined are known as spatial discrimination.

The flight crew in LINK285 looked ahead for LINK235 where they expected it to be and saw an aeroplane. They agreed it was LINK235 but they had likely experienced confirmation bias. Confirmation Bias is the tendency to look for information that supports, rather than rejects, one’s preconceptions, typically by interpreting evidence to confirm existing beliefs while rejecting or ignoring any conflicting data (Noor, 2020).

Both the pilot flying and pilot monitoring LINK285 recalled in separate interviews that the pilot flying had located the aircraft ahead (this was JST290) and pointed it out to the pilot monitoring. The pilot flying recalled that, initially, the pilot monitoring had had difficulty identifying the aircraft ahead, but eventually they had both believed it was LINK235.

The LINK285 flight crew had other information available that conflicted with their agreed identification of LINK235 at this time, but they did not focus their attention on it. For example:

- the LINK285 flight crew heard the approach controller pass the control of JST290 to the tower immediately before receiving their own clearance to descend. That meant they were one of three aircraft in the landing sequence. They had identified one aeroplane in front, but where was the other?

- the Dash-8 ahead was described by the approach controller as turning onto base leg, but the A320 that they thought was LINK235 was on its final approach. This was a different position in the landing pattern, and it was heading in a different direction from LINK235

- there is a significant difference between the shape of a Dash-8 and that of an A320.

The TCAS would have displayed information that also conflicted with the crew’s mental model. The TCAS range was set to detect and display other aircraft with transponders in a 12 nm radius of airspace around the aeroplane. Both JST290 and LINK235 were about 6 nm away from LINK285 and their targets would have been visible on the TCAS display as open or solid, cyan-coloured diamonds. The pilots in LINK285 said they did not check their TCAS display until after they saw an unexpected object to their left. They used the TCAS to confirm it was an aircraft target.

The LINK285 flight crew’s reliance on the visual identification of the aeroplane they had been directed to follow, without considering alternative sources of verification, led to their misidentifying that aeroplane. Once the flight crew had convinced themselves they were following the correct aircraft to land, the sudden realisation that they were wrong had a startle effect on them. All participants in this incident were stood down from duty afterwards, to allow them to recover.

The TAIC also annotated: "The Commission is concerned that operators are not recognising the importance of CVR records and the value they can provide to post-incident and -accident investigations and learning." and analysed:

In this incident the operator allowed both aircraft to fly their next legs before the CVRs were disabled. Both aircraft were on the ground for about 30 minutes after landing, then flew the next flight legs of about 40 minutes’ duration. As a result of these delays in isolating the CVRs, critical voice recordings from the time of the incident were lost and others were difficult to separate and interpret.
Incident Facts

Date of incident
Mar 12, 2019

Classification
Report

Flight number
NZ-285

Departure
Gisborne, New Zealand

Destination
Wellington, New Zealand

Aircraft Registration
ZK-NEF

Aircraft Type
De Havilland Dash 8 (300)

ICAO Type Designator
DH8C

This article is published under license from Avherald.com. © of text by Avherald.com.
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