"The captain's skill in conducting the engines-out glide to a successful landing averted a catastrophic accident and saved the lives of the passengers and crew," the report says.

However, the report makes clear that such heroics would not have been needed had the pilots shut down the right-side engine (where the fuel was leaking) or had not pumped tonnes of fuel from the undamaged left wing into the right-wing tanks, from where it was poured overboard at more than three kilograms a second.

"Either of these actions would have conserved the fuel in the left-wing tanks and allowed for a landing at Lajes with the left engine operating," the report says.

Instead, "opening the crossfeed valve put the fuel in the left tank at risk, and initiated a worsening of the serious fuel-leak situation."

The crew failed to comprehend that the aircraft had a major fuel leak, even after the second engine died.

"Notwithstanding indications that there had been a massive loss of fuel, the crew did not believe that there was an actual fuel leak," the report says. Instead, the crew believed they were dealing with a computer malfunction.

Details of the flight-crew conversations were lost to investigators because the pilots inadvertently recorded over the 90-minute cockpit voice tape after the landing.

Investigators established that fuel began leaking from the twin-engined, wide-bodied jet more than an hour before the pilots noticed anything amiss. When they did, they treated the problem as a fuel imbalance and failed to heed the checklist warning of fuel-leak possibility.

They did not call up the checklist on the computer screen, relying instead on memory for their actions. Fifteen minutes later, with the fuel level dropping alarmingly and below the minimum needed to reach Lisbon, the crew elected to divert to the Azores. But they continued to transfer the dwindling fuel from the left wing to the leaking right side.

At 6:13 a.m., with the aircraft more than 240 kilometres from Lajes, the right-side engine flamed out for lack of fuel. At 6:23, the crew radioed a full-scale mayday. Flight attendants were told to prepare the passengers for a ditching. Three minutes later, more than 100 kilometres from the nearest land, the left engine flamed out. During the next 19 minutes, in darkness and with only limited instruments, Capt. Piché nursed the unpowered aircraft to a landing.

Investigators determined that the fuel leak was caused by improper installation of the right-side engine nearly a week earlier. Air Transat technicians, dealing with a slightly different model of Rolls-Royce engine than they were familiar with, had improperly attached fuel and hydraulic lines to the engine. The lines chafed, eventually fracturing the fuel line.

The report says that the Air Transat flight crew were inadequately prepared to recognize and deal with fuel leaks.

"The flight crew members had never experienced a fuel leak situation during operations or training," the report says, adding the "lack of training in the symptoms of fuel-leak situations resulted in this crew not being adequately prepared."