AIRASIA X has defended the conduct of its pilots amid a probe into why two passenger flights dropped below safe altitudes over the Gold Coast.
The Australian Transport Safety Bureau (ATSB) says the incidents are "serious" and subject to a full investigation.
Registration records show one of the planes was an AirAsia X plane, enroute from Kuala Lumpur in Malaysia.
The 330-seat Airbus dropped "below the radar lowest safe altitude" over the Gold Coast at 7.30am (AEST) on May 4, the ATSB said.
At the the time, the plane was flying on instruments due to poor visibility.
The ATSB said it was also investigating a similar incident involving the same aircraft type on May 3.
AirAsia X chief executive officer Azran Osman-Rani said passenger safety was never at risk during either incident.
"We do not believe that passenger safety was compromised at any time and landings were performed normally under guidance from air traffic controllers," he said.
"AirAsia X has been advised by the ATSB that this is a routine investigation only.
"We have supplied our flight data which they will then analyse and compare with air traffic control data to find any anomalies."