Passengers on an Air Canada flight had a nail-biting four hours in the sky circling on just one engine after the other one burst into flames shortly after takeoff from Madrid.

The Toronto-bound flight AC837 took off shortly after 12:30pm local time, when the captain reported multiple technical problems. The left engine of the Boeing 767-300 began expelling smoke and flames. One of the tyres also reportedly burst on take-off.

It is not clear what caused the issues with the aircraft but they both happened as the plane was leaving Barajas International Airport.

So this happened: Passenger Aaron C. reported a loud bang on takeoff. Photo / Twitter
So this happened: Passenger Aaron C. reported a loud bang on takeoff. Photo / Twitter

The trans-Atlantic service was forced to spend four hours flying holding patterns while it burned off enough fuel to attempt an emergency landing.

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One passenger captured video of flames under the left plane wing. Posting a screenshot to Twitter he wrote: "Just at take-off there was a huge bang under my seat and then I saw smoke and flames from the left engine."

Spain's defence ministry sent an F18 fighter jet to help the Air Canada Pilots assess the damage to their landing gear before they attempted an emergency landing.

Landing shortly after 7pm local time, the plane was met on the ground at Adolfo Suarez-Barajas Airport by emergency services.

"Pretty scary rough landing, but we made it," one passenger described the experience on Twitter.

"Obviously a lot of nervous tension while we were in the air, but the pilots did a terrific job landing the plane," Canadian passenger Brock Mierzejewski told Associated Press.

While the plane prepared to land, Air Canada issued a statement confirming that flight AC837 "experienced an engine issue shortly after take-off." The airline also reported the "ruptured" tire, but assured media that it was just "one of 10 on this model of aircraft," and the aircraft was designed to handle this redundancy.

"The Boeing 767-300, is designed to operate on one engine and our pilots are fully trained for this eventuality. Nonetheless, and emergency was declared in order to obtain landing priority," said the airline in a statement.

The 128 passengers all landed safely following the four-hour wait in the air.

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Madrid's international airport is the busiest in Spain, and that Monday was particularly hectic. The emergency landing of AC837 came just hours after airspace was closed following a reported drone sighting.

Holding patterns vs fuel dumps

In order to perform an emergency landing, most planes must reduce their weight. The easiest way of doing this is to reduce fuel weight.

Holding pattern: The Boeing 767-300 had to burn off four hours of fuel before it was light enough to land. Photo / Flight Radar
Holding pattern: The Boeing 767-300 had to burn off four hours of fuel before it was light enough to land. Photo / Flight Radar

Trans-Atlantic flights use up around 50 metric tonnes of fuel in a crossing, which makes them too heavy to land safely.

While some long-range planes are able to dump or 'jettison' fuel, the 767-300 does not have the ability perform a fuel dump, and so pilots had to perform holding patterns until it was deemed light enough to land.