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Final Report

Summary

On the morning of 22 February 2017, a Singapore Airlines Boeing 777-212, registered 9V-SRP, operated scheduled flight SQ291 from Singapore Changi Airport, Singapore, to Canberra Airport, Australian Capital Territory (ACT). There were 13 crew and 235 passengers on board.

Prior to descent to Canberra Airport, the flight crew prepared to conduct the Standard Arrival Route (STAR) POLLI FOUR PAPA arrival and associated RNAV-Z approach.

As the aircraft descended, air traffic control (ATC) instructed the flight crew to conduct the POLLI FOUR BRAVO arrival.

As the arrivals were very similar, the flight crew elected to reprogram the POLLI FOUR BRAVO arrival into the FMC while keeping the RNAV-Z approach. This created a discontinuity in the programmed FMC flight path. To correct this discontinuity, the captain connected waypoint MENZI to the approach at waypoint SCBSI. In doing so, the waypoint SCBSG was erased from the programmed FMC approach.

The RNAV-Z approach via SCBSG must be commenced from an altitude at or above 7,500 ft. This altitude constraint is included in the FMC programmed flight path when selecting an approach using the arrivals/departures page in the FMC. The captain manually re-entered SCBSG into the FMC without detecting that the 7,500 ft constraint was now missing. The captain then manually connected SCBSG to SCBSI for the continuation of the approach.

At 0909.16, the aircraft tracked towards SCBSG the aircraft descended below 7,500 ft. At 0909.37, as the aircraft descended to about 7,000 ft, the flight crew immediately disconnected the autopilot and climbed the aircraft to 7,500 ft.

At 0911:24, after the aircraft passed SCBSG the aircraft commenced descending. The segment minimum safe altitude for the leg of the approach from SCBSG to SCBSI was 5,300 ft.

At 0912.37, as the aircraft continued on the segment between SCBSG and SCBSI the aircraft descended below 5,300 ft. As the aircraft descended to about 4,600 ft the first officer levelled the aircraft. The flight crew advised ATC that they had the runway and terrain in sight. The controller then cleared the flight to conduct a visual approach.

At 0917, the aircraft landed on runway 35. The aircraft was not damaged and no persons were injured.

This incident highlights the importance of preparation and communication prior to commencing a phase of flight. Requesting a preferred clearance early allows ATC to ensure that a clearance can be provided, or if not available, allows the flight crew time to prepare for a different clearance.

This incident also underlines the importance of adhering to standard operating procedures (SOPs). By deviating from SOPs and manually entering the waypoint the crew removed a protection which was in place to prevent data input errors.

 

Aviation Short Investigations Bulletin Issue 61

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