Qantas sources said they did not know how five rats found their way aboard a jet yesterday.

Qantas sources said they did not know how five rats found their way aboard a jet yesterday. Photo: Louie Douvis

QANTAS has been forced to ground one of its passenger jets after rats were found on board.

Flight attendants found five rats in the cabin of a Boeing 767 aircraft due to leave Sydney on Tuesday afternoon while making a routine safety and security inspection.

The rodents were discovered in emergency medical equipment carried on the aircraft, 10 minutes before passengers were due to board. Qantas was unsure last night how the rats got there.

The airline grounded the plane at Sydney Airport while staff killed the rats and searched the cabin to ensure no more were on board.

The passengers, bound for Brisbane on the 5pm flight from Sydney on Tuesday, were transferred to another aircraft.

Engineers were still inspecting the 767 yesterday to determine whether any damage had been caused to wiring and the aircraft systems.

But Qantas said it expected the jet to return to service this morning.

''We still don't know how they got on board but it is obviously not a common occurrence,'' a Qantas spokesman said last night.

''They are pretty confident we can get it back into service [today].''

Industry insiders said rats could damage aircraft wiring.

''Once they get into an aircraft they are hard to get rid of because of all the nooks and crannies,'' one said.

The Civil Aviation Safety Authority is understood to have been informed of the temporary grounding.

But Qantas said last night that the 767 was unlikely to have to be stripped down to determine whether the rats had caused more extensive damage.

It is the latest setback for Qantas, which faces questions over its decision to drop flights to San Francisco in favour of a non-stop leg between Australia and Dallas.

A Qantas 747 jumbo was forced to make an unscheduled stop on the Pacific island of New Caledonia this week when it was found to be running low on fuel.

The 13,816-kilometre route, which Qantas launched two weeks ago, is at the upper limit of the 747-400 jumbo's flying range.

The Dallas service is one of the longest non-stop routes in the world and the longest flown by 747 jumbos.