At 2102 Eastern Standard Time on 7 June 2011, an Airbus A320 aircraft, registered VH-VNG and operated by Tiger Airways, was on an approach to runway 27 at Melbourne Airport, Victoria. Air traffic control (ATC) had cleared the aircraft to descend to 2,500 ft. Shortly after, ATC identified that the aircraft had descended to 2,000 ft, which was below the limiting altitude for that segment of the approach. ATC notified the flight crew of the deviation. The crew re-established the aircraft at 2,500 ft, then continued the approach and landed.
What the ATSB found
The ATSB found that the flight crew had based the descent profile on information displayed on the aircraft’s Multipurpose Control and Display Unit (MCDU). The MCDU drew on information stored in the aircraft’s flight management guidance system (FMGS). The FMGS information included data provided through a third party that had a missing altitude limitation; that limitation was, however, included in the paper charts also used by the crew. The data error was not identified by the crew during their preparation for the approach.
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. In addition, different assumptions by the data suppliers and the operator compromised the quality assurance of the navigational data.
The action by ATC to alert the flight crew triggered their recovery from the descent below the required flight profile.
What has been done as a result
In response to this occurrence, the operator implemented an auditable process for identifying and managing any navigational database anomalies in its aircraft fleet.
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. The accurate application of those procedures by all key personnel is also important as a safety defence.