An incorrect flight mode setting was the main catalyst for a loss of separation between a Virgin Australia Boeing 737-800 and a Jetstar Airways Airbus A320 while on final approach into Sydney.

The incident occurred on 4 June 2013, and involved an 737, registered VH-YIR, and an A320 registered VH-VFL, the Australian Transport Safety Bureau (ATSB) says in its final report on the occurrence.

The Virgin 737 was on an independent visual approach (IVA) to Sydney airport’s runway 16 Right. As it approached the extended centre-line of the runway, the airport’s traffic collision avoidance system (TCAS) provided a traffic alert and a resolution advisory in relation to the Jetstar A320, which was on approach to runway 16 Left.

In accordance with the advisory, the pilot flying the 737 descended until the TCAS alert ceased, and captured the extended centre-line from the other side, while the crew of the A320 executed a go-around.

Both aircraft were operating in IVA procedures, and so the incident did not constitute an air traffic control loss of separation assurance.

In its investigation, the ATSB found that the 737 passed through the centre-line because its automatic flight control system was not set in the correct mode to intercept and turn onto the runway localiser.

“This most likely occurred due to insufficient force being applied to the approach mode push-button and, as the flight crew did not perform an effective check of either the mode control panel or the flight mode annunciator to verify a mode change, they were unaware that the aircraft’s flight mode was not set as intended,” it adds.

ATSB also found that the risk of an undetected mode selection was higher as Virgin did not require flight crew to announce flight mode changes.

Virgin subsequently amended its policy so that changes to the flight mode annunciator are announced by the pilot flying, and the pilot monitoring should announce any changes missed by the pilot flying.

Source: Cirium Dashboard