MONTREAL -- A Boeing 747 test plane owned by Pratt & Whitney that was having technical problems was forced to dump 20,000 litres of fuel before landing.

The fuel was dumped into the Macaza region of Quebec's Laurentian Mountains.

According to results from a preliminary investigation that was obtained by QMI Agency, the plane was having problems with its second engine and its compressor when the pilot was ordered to fly north and dump the fuel from the airplane. At the same time, the control tower at Mirabel airport informed the plane that smoke could be seen coming from the plane's engines.

Investigators told QMI Agency that the aircraft had to dump the fuel or it would not have been safe to land.

The amount of fuel dumped, 20,000 litres, is the same amount of fuel that an oil tanker holds.

Following procedure, the plane turned off the second engine and then climbed to 16,000 feet to dump the fuel, minimising the environmental impact. A study conducted by the Canadian Armed Forces says that if fuel is dropped from this height, only 1.5% to 9% of the fuel will hit the ground. The rest will evaporate.

The plane, which had 14 passengers on board, landed about an hour after the incident began.

Nancy German, a spokesperson with Pratt & Whitney, told QMI Agency that "there was a small abnormality on takeoff." German also said that it was impossible to "precisely state the amount of fuel that was dumped mid-air, but that practically no fuel" actually hit the ground.