[caption id="attachment_12107" align="aligncenter" width="572" caption="The position of the Tiger flight at 9.01.59 pm about when it breached the safe minimum altitude"]
The approach and departure air space traffic controllers at Melbourne Airport last night warned a Tiger Airways A320 that it was too low as it descended over Epping prior to turning toward its final approach to the runway at the end of a flight from Brisbane.
The incident is now under investigation by the ATSB, which has classed it as an 'operational occurrence' rather than a 'serious incident', and timed it at 9.02 pm.
The air safety investigator says the jet, an A320 which carries up to 180 passengers and at least six crew, descended below the safe minimum height for the approach it was flying to the airport while close to the airport.
The incident occurred during a burst of cold and rainy, even sleety conditions in the area.
A review of the community aircraft tracking web site archive for last night shows the Tiger flight promptly descending from 10,000 feet, when it becomes visible on the service, and flying a path that airliners are typically given when lining up to land from the east on the east-west runway.
The jet descended to at least 2182 feet (above sea level) while more or less aligned with the Epping Road and flying south at 9.02 pm, which is in breach of the minimum altitude requirement at that point, and then, as it turned toward the airport, climbing to more than 2500 feet over Thomastown before resuming its descent over Campbelltown.
If the altitudes shown in the web track archive are compared to terrain altitudes found on Google Earth (and neither can be relied upon as being accurate to within a metre) it appears that the Tiger flight could have been somewhere between 1500 and 1700 feet above ground in the vicinity of Epping, or notably lower than normal or legal in that area for a passenger carrying jet.
The exact values, and the reasons why Tiger busted the safe minimum altitudes, may take a year to determine according to the ATSB website, which posts estimates of the time needed to complete its current investigations based on its work load.
It isn't know if the ground proximity warning system on the A320 was triggered during this incident. Tiger Airways has issued a brief statement saying that it reported the incident, was cooperating with the ATSB, and would not comment further at this stage.