The Australian Transport Safety Bureau (ATSB) has, in a preliminary report, found that a discrepancy between descent guidelines led to a Tiger Airways Airbus A320 having a lower descent altitude than recommended while landing at Melbourne Airport on 7 June.
The aircraft, with the registration VH-VNG, was en-route from Brisbane and was cleared by Melbourne Airport air traffic control (ATC) to conduct an Arbey One Alpha arrival to land on runway 27.
The captain handed over controls to the co-pilot about 10 minutes before descent. He then referred to instrument navigation charts that were supplied by Jeppesen in paper format, and entered the arrival approach and landing procedures into the flight management guidance and envelope system (FMGS) via the Multifunction Control and Display Unit (MCDU).
The FGMS calculated the approach path using its internal navigational database. The commander briefed the co-pilot on the planned approach by reading out the details of the approach from the MCDU, and the co-pilot checked that against the paper format approach.
"The flight crew did not notice that the documented arrival procedure had a lowest descent altitude of 2,500ft, while the data from the FGMS's navigational database that was displayed on the MCDU had a lowest descent altitude of 2,000ft," said the ATSB.
The aircraft continued to descend to 2,500ft, shortly before turning from downwind to base on the arrival procedure. The chief pilot reported that as that happened, the MCDU showed that the planned altitude of descent was 2,000ft, and he set that on the flight control unit (FCU). He notified the co-pilot, who was still in control, by calling "two thousand" and that was confirmed. This was also verified on both the FCU and MCDU.
"The aircraft was approaching 2,000ft, when ATC advised the flight crew that they should be at 2,500ft and instructed them to climb to 2,500ft. The flight crew climbed the aircraft to 2,500ft and continued the approach and landed on runway," said the ATSB.
Investigations into the navigational database found that the FMGS included two copies of a commercial navigational database, which was updated on a 28-day cycle as a part of normal scheduled maintenance.
"The investigation established that the navigational database that was current for the flight included a lowest descent altitude for the Melbourne Arbey One Alpha runway 27 arrival of 2,000ft," said the ATSB.
The ATSB added that investigations will continue. These will include the analysis of recorded flight data, recorded air traffic control data, examination of the operator's procedures, and investigation on of the data integrity management system for the navigational database. It did not say when a final report will be released.