The Australian Transport Safety Bureau is investigating an incident involving a Tiger Airways Airbus A320. Flight TT 5207 with approximately 150 people on board had flown from Brisbane to Melbourne where the incident occurred at 9:02pm, yesterday.

The Australian Transport Safety Bureau says the aircraft "descended to a level below the lowest safe altitude" during an instrument approach.

An online aircraft tracker shows the aircraft had descended to 2201 feet over the northern suburbs of Melbourne where minutes later, the altitude of aircraft on similar flight paths in the same area is around 1000 feet higher.

In March this year, the Civil Aviation Safety Authority (CASA) issued Tiger with a show cause notice, believed to be focussed on pilot training standards and aircraft maintenance.

An airline spokesperson said yesterday, "Tiger Airways is fully cooperating with the investigation."