Pilots on a Singapore Airlines (SIA) flight en route to Canberra, Australia, in February have been found guilty of flouting safety procedures.

The Boeing 777 aircraft that they were piloting flew not once, but twice, below the stipulated lowest safe altitude, Australia's aviation safety body said in a report yesterday.

After an investigation, the Australian Transport Safety Bureau (ATSB) said that while none of the 235 passengers and 13 crew on board were hurt, and there was no damage to the aircraft, the incident uncovered some operational lapses.

Flight SQ291 was approaching Canberra Airport on Feb 22 when the incident took place about 20km from the airport.

The pilots were preparing to descend when air traffic control instructed them to make some changes to the arrival path.

As the initial and new paths were very similar, the pilots did not take all the necessary steps to reprogram the systems.

This eventually led to the aircraft descending below the stipulated altitude at one point. When the flight crew realised this, the pilots immediately disconnected the autopilot and took the aircraft to 7,500 ft.

A few minutes later, the plane again flew to below the stipulated altitude. The flight eventually landed safely at the airport. ATSB said in its report: "This incident highlights the importance of preparation and communication prior to commencing a phase of flight."

It also underlines the importance of adhering to standard operating procedures, the authority said.

A spokesman for SIA told The Straits Times: "We will use the findings from the ATSB report to educate and raise awareness among our crew." The safety of passengers and crew is always the top priority, he said. SIA did not say if any action had been taken against the pilots.

For all flights, pilots have to ensure that the aircraft does not fly below the stipulated lowest safe altitude, experts say. This is to keep the plane at a safe height above an obstacle or terrain when landing approaches, they add.

The actual altitude depends on flight rules set by different air traffic regulators, and the highest obstacle or terrain along the flight path.

Typically, it is at least 1,000 feet above the highest obstacle.