Qantas landing 'very serious'

Qantas has stood down two pilots pending an investigation into why they didn't activate the landing gear on a Boeing 767 when approaching Sydney airport from Melbourne last Monday.

The plane was less than 300 metres above the ground when its onboard computer system warned the pilots with the words "too low - gear, too low - gear".

The pilots regained altitude and circled the airport before landing safely shortly after.

The Australian Transport Safety Bureau confirmed to AAP it was investigating the incident.

This is "what we call a routinely reportable event," a spokesman for the bureau told AAP.

Australian and International Pilots Association president and Qantas pilot Barry Jackson said it was "very serious" if the enhanced warning system was activated.

"It's designed to go off when an aircraft is close to the ground. It's not configured for landing."

While not commenting specifically on the incident being investigated, Mr Jackson said the busiest parts of any flight were take off and landing.

"You're dealing with air traffic, you're dealing with slowing the aircraft down, you're dealing down, configuration changes, changing frequencies," he said.

Mr Jackson said several details were unclear, including whether the plane started to climb immediately after the warning.

Qantas has issued a statement describing the incident as a "brief communications breakdown".

The safety bureau is expected to deliver a preliminary factual report in about a month.