Data anomalies and a deficiency in Tiger Airways Australia's safety management system have been cited as key contributors to an incident where an Airbus A320 aircraft flew below the limiting altitude while on approach to Melbourne's Tullamarine airport in June 2011.
The aircraft, with registration VH-VNG, was completing an approach to runway 27 on 7 June 2011 and was cleared by air traffic control to descend to 2500ft (762m), according to the final report into the incident by the Australian Transport Safety Bureau (ATSB)
The aircraft, however, was observed at 2000ft, below the limiting altitude for that segment of the approach.
Air traffic controllers notified the flight crew, who returned to 2500ft and continued their approach, landing safely a short while later.
The ATSB investigation found that an anomaly in the aircraft's flight management guidance system data meant the limiting altitude was not displayed on the aircraft's multipurpose control and display unit, although it was printed on the crew's paper charts.
"The ATSB also found there was an increased risk of inadvertent non-compliance with published instrument approach procedures because of the inconsistent application of the operator's safety management system to the identification and management of database anomalies," it says.
The report adds that as a result of the investigation, Tiger has implemented an auditable process for identifying and managing navigational anomalies in its database as part of its safety management system.
"This occurrence reinforces the safety benefits of a resilient safety management system and operator procedures in the management of safety-critical database and other information," says the ATSB.
"The accurate application of those procedures by all key personnel is also important as a safety defence," it adds.
The incident, which followed other safety breaches, led the Civil Aviation Safety Authority to ground the carrier from 2 July 2011 to 12 August 2011.