The Australian air safety authority has launched a probe into an incident involving a Singapore Airlines (SIA) aircraft.
Flight SQ291 was approaching Canberra Airport on Feb 22 when the pilot brought the Boeing 777 below the stipulated lowest safe altitude.
The incident happened about 20km from the airport.
While there were no injuries and the plane was not damaged, the Australian Transport Safety Bureau (ATSB) was alerted to the incident and is investigating, a spokesman told The Straits Times.
SIA confirmed that it has been approached by the authority.
"We are extending our full co-operation on this incident," said SIA spokesman Nicholas Ionides.
It is unclear how the lapse occurred and whether it was detected by the cockpit crew themselves or by air traffic controllers.
Neither the authority nor airline would shed more light on the matter, citing ongoing investigations.
For all flights, pilots have to ensure that the aircraft does not fly below the stipulated lowest safety altitude.
This is to keep the plane at a safe height above an obstacle or terrain during landing approaches, said qualified pilot and founder of Revion (flight) Ground School, Toh Youhao.
The actual altitude depends on flight rules set by different air traffic regulators and also the highest obstacle or terrain along the flight path.
Typically, it is at least 1,000 feet above the highest obstacle.
The safety buffer is critical as it allows for errors in the air by including an additional area that a pilot might stray into, experts noted.
Mr Toh said: "It is the job of the pilots to find out what the lowest safety altitude is.
"The information is provided in the pre-flight package and also available in flight charts that pilots can access."
The Australian authority is expected to complete its probe into the SIA incident and issue a report by June.
The report will likely detail the circumstances that led to the incident and point out lapses that should be rectified
The ATSB gets thousands of reports each year but investigates only those that are deemed more serious.
It is currently probing 112 aviation incidents.
This article was first published on March 1, 2017.
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