An Air Canada passenger jet that was forced to make an emergency landing in Toronto earlier this week likely dumped many tonnes of fuel over Lake Ontario before the aircraft touched down safely.

That’s according to Ravin Appadoo, a Montreal-based consultant who advises the International Air Transportation Association and the United Nations on aviation-fuel issues.

Air Canada did not reply to CBC News queries about the amount of fuel on the plane or how much was jettisoned. Appadoo estimates that the Tokyo-bound Boeing 777 would have been carrying between 70 and 80 tonnes of jet fuel when it took off, on what was supposed to be a 12-hour flight from Pearson International Airport on Monday.

A tonne of jet fuel sells for about $1,000 Appadoo said, meaning the airliner could have had as much as $80,000 worth in its tanks when it took off.

Shortly after takeoff, the plane had to shut down one of its engines, Air Canada said.

Pieces of metal debris from a turbine aboard the troubled aircraft fell to the ground, an investigator with the Transportation Safety Board of Canada said Tuesday. The small pieces of metal are believed to have damaged several cars in the area.

The plane eventually landed back at Pearson after circling over Lake Ontario and dumping fuel.

Weight problem

Appadoo said the intercontinental airliner isn’t designed to land with its tanks full because it would be too heavy.

"For sure, the cockpit crew did not jettison all its fuel in the tanks, but enough to lighten the aircraft" sufficiently so that landing wouldn't threaten "the structural integrity of the plane," he said.

“Making a technical stop with that amount of fuel, it would not be safe.”

The aircraft is equipped with a fuel-dumping system for emergency situations that can pump fuel out of the wings or from the tail.

Federal aviation regulations say that jet fuel should be jettisoned only if it's necessary to "ensure aviation safety" and that "all appropriate measures" must be taken to minimize danger to humans and the environment. A plane must be travelling at least 609 metres above the highest obstacle within five nautical miles, and should dump its fuel over unpopulated areas, Transport Canada says.

Appadoo added that the fuel would most likely vaporize in the air and dissipate in the atmosphere.

“I don’t think it would fall as jet fuel on the ground or whatever,” he said. “But they would have to [dump fuel] at a high altitude before descending.”

Kate Jordan, a spokesperson for the Ontario Ministry of the Environment, said the province's air-quality monitoring stations on the ground saw no elevated readings of ozone after the plane landed. Jet fuel is made up volatile organic compounds, which are ingredients in smog-causing ozone.