The aircraft, operated by Virgin Australia from Los Angeles, had been performing the LIZZI 7V standard arrival pattern to runway 34.
This arrival pattern, which had been programmed into the flight management computer during cruise, ended at a waypoint designated SHEED, so the crew supplemented the pattern by selecting a visual approach from the database.
Selecting this option added another pair of waypoints to extend the pattern beyond SHEED: one at the runway threshold and one, fixed by the crew, positioned 2.8nm before the runway.
The threshold waypoint’s altitude defaulted to 330ft but the carrier’s procedures advised pilots to adjust this to 380ft, to provide a 50ft threshold crossing height.
But investigators state that the pilots instead mistakenly assigned this 380ft altitude to the second waypoint, the height for which was normally automatically calculated by the flight computer.
As a result, after passing the SHEED waypoint, the aircraft’s autopilot increased the rate of descent from 700ft/min to 1,500ft/min in order to lose height and cross the 2.8nm waypoint at 380ft.
This sudden rapid descent surprised the crew, who noted that the aircraft was too low for the approach. The captain disengaged the autopilot and levelled the 777 at 700ft – some 500ft above ground – and flew at this height until precision-approach path indicator lamps showed the jet had intercepted the glidepath. It landed safely.
Four flight crew were in the cockpit during the approach. Australian Transport Safety Bureau investigators are still assessing the 15 August 2013 event, adding that the inquiry will focus on how the data was incorrectly entered and “remained undetected”.
(David Kaminski-Morrow - Flight Global)