VH-YIR Loss of Separation due to Incorrect Flight Mode
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11 Aug 2015 - The ATSB has published its final report into the flight path management occurrence involving Boeing 737-800, VH-YIR that failed to intercept the localizer at Sydney Airport on 4 Jun 2013 leading to a loss of separation with an aircraft on approach to the parallel runway.
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.
The full report is available here
Vertical profile of the flights (ATSB Report)
On 4 June 2013, a Boeing 737-800 (737) aircraft, registered VH-YIR and operated by Virgin Australia (Virgin), was on a scheduled passenger service from Melbourne, Victoria to Sydney, New South Wales. During descent into Sydney, the crew was advised by air traffic control (ATC) to expect an independent visual approach (IVA) to runway 16 Right (16R). As the aircraft approached the extended centre-line of runway 16R, the aircraft's traffic collision avoidance system (TCAS) provided a traffic alert followed by a resolution advisory (RA) in relation to an Airbus A320 aircraft on approach to parallel runway 16 Left (16L). As the crew commenced descent in response to the RA, the aircraft continued through the extended centre-line of runway 16R by about 300 m. When the TCAS alert ceased, the pilot flying captured the extended runway centre-line from the other side. The flight crew continued the approach and landed, whilst the A320 executed a go-around procedure. As both aircraft were cleared and utilising IVA procedures, the occurrence did not constitute an ATC loss of separation assurance.
What the ATSB found
The ATSB found that the 737 passed through the centre-line as a result of the aircraft's automatic flight control system not being set to the correct flight mode for an intercept and turn onto the runway 16R 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. The ATSB also found that the risk of an undetected mode selection error was increased as the Virgin procedures did not mandate that flight crew announce flight mode changes. There were no technical failures of the aircraft, aircraft tracking systems or ground equipment in relation to this occurrence..
Whats Been Done as a Result
In response to this occurrence, Virgin introduced a flight policy requiring crews to verbally announce flight mode changes when operating above 500 ft
During an IVA, accurate interception and tracking of the runway centre-line is essential to maintain separation with aircraft using the parallel runway. This occurrence highlights the importance of pilots remaining vigilant during this type of approach, including to the consideration of and response to all RAs. The importance of crews conducting comprehensive checks of the mode control panel and flight mode annunciator to ensure that the flight mode selected is consistent with the crew's intention is also reinforced..
From the evidence available, the following findings are made with respect to the flight path management occurrence involving Boeing 737, registered VH-YIR and operated by Virgin Australia, which occurred at Sydney Airport, New South Wales on 9 June 2013. These findings should not be read as apportioning blame or liability to any particular organisation or individual. Safety issues, or system problems, are highlighted in bold to emphasise their importance. A safety issue is an event or condition that increases safety risk and (a) can reasonably be regarded as having the potential to adversely affect the safety of future operations, and (b) is a characteristic of an organisation or a system, rather than a characteristic of a specific individual, or characteristic of an operating environment at a specific point in time..
The flight crew applied insufficient force to the approach mode push-button on the mode control panel to arm the mode, which was not identified during their subsequent check of the flight mode annunciator.
Due to their expectation that the aircraft approach mode was armed, and a subsequent degradation in monitoring the aircraft's systems, the flight crew did not anticipate that the aircraft's automated systems would not capture the runway 16R localiser and did not immediately detect the flight path deviation.
The flight crew did not recognise that the traffic advisory alert provided by the aircraft's traffic collision avoidance system 12 seconds prior to the aircraft passing through the runway centre-line was a potential indication of a problem with the aircraft's flight path.
Other factors that increased risk
The Virgin Australia procedures did not require its flight crew to, whenever practicable, announce flight mode changes. [Safety issue]
Air traffic control did not, and was not required to provide traffic information to aircraft using adjacent runways and abeam each other during independent visual approach procedures at Sydney. [Safety issue]
Relative to other approaches or flight operations, there is a relatively high rate of traffic collision avoidance system resolution advisory alerts during independent visual approaches at Sydney Airport.