The discovery of five baby rats in a cabin compartment on a Qantas jet has caused a flight to be grounded.Air crew found the rats minutes before passengers were due to board a Boeing 767 flying from Sydney to Brisbane.The airline said it was a rare occurrence and passengers were put on another plane while the rats were disposed of.Qantas has suffered several mishaps in recent months, none of them causing any loss of life.A Qantas spokeswoman said engineers had checked the plane and found the rats had done no damage."We don't know how they got there. The aircraft was at the gate for some time before departure and we are investigating," she told AFP."It is a rare occurrence. We have no record of it ever happening before."Qantas Airways warned earlier this year that profits at the company would be hurt by the recent natural disasters in Japan, New Zealand and Australia.One of Qantas' superjumbos made an emergency landing after experiencing engine trouble shortly after taking off from Singapore on its way to Sydney last November.The airline grounded all six of its fleet of Airbus A380 airliners to carry out safety inspections.Source: BBC