HALIFAX -- As Air Canada Flight 624 made its final, ill-fated approach toward Halifax's main airport in a raging blizzard, no one in the cockpit was checking the plane's altitude or distance from the runway.
The pilots had no idea the aircraft, carrying 133 passengers and five crew, had strayed from its intended flight path and was flying too low.
"It was only in the last few seconds of the flight, after the pilots disengaged the autopilot to land manually, that they then realized the aircraft was too low and too far back," the Transportation Safety Board of Canada concluded in a final investigation report released Thursday, more than two years after the crash landing.
The report cited several other factors in the 2015 crash, including problems with runway lighting and something the board called "plan continuation bias."
And it described in gripping detail what happened when the flight crew realized the aircraft was about to hit the ground.
The captain poured on the thrust and pulled back on the stick to gain altitude for a go-around, but it was too late.
A second later, one of the jet's tires hit an approach light about 260 metres from the runway threshold, and the aircraft clipped some power lines, knocking out power to the airport. The jet's main landing gear and left engine then struck a snowbank and the Airbus 320-211 smashed into an antenna array before bouncing twice along the Runway 05 for another 600 metres amid a shower of sparks and leaking fuel.
The landing gear collapsed, an engine was torn off, but there was no fire.
The crash, described at the time as a "hard landing" by Air Canada, left 25 passengers injured. The aircraft was destroyed.
"Because no emergency was expected, the passengers and cabin crew were not in a brace position at the time of the initial impact," the report says. "Most of the injuries sustained by the passengers were consistent with not adopting a brace position."
The board's report says the aircraft, en route from Toronto, was circling the airport just after midnight on March 29, 2015, when the crew received word from the tower that visibility in the snowstorm had improved to just under one kilometre -- the minimum requirement for a landing.
As the plane approached the airport, it was placed in autopilot mode. As well, the flight crew was relying on the "localizer" radio beacon near the runway, which provides only lateral guidance to align the aircraft with the centre line.
In this configuration, the autopilot adjusts the aircraft to maintain its flight path approach angle -- in this case 3.5 degrees -- and the localizer tells the pilots whether to steer left or right to keep in line with the runway.
Neither device provides information about altitude or distance.
"What a localizer does not provide is vertical guidance," said senior investigator Doug McEwen. "That is up to the flight crew. They must refer to their instruments to ensure they are at the correct height relative to the distance from the runway."
Kathy Fox, chairwoman of the TSB, said the pilots did not take into account that a headwind was pushing the plane off of its intended flight path.
"Because the wind was pushing the airplane back, it ended up being lower and farther out," she said. "They did not notice that they had moved away from where they needed to be."
Under Air Canada's standard operating procedures, the captain and first officer were not required to cross-check their altitude and distance, which Fox described as a procedural "gap" that has since been closed. Fox noted the flight crew operating manuals used by Air Canada and Airbus do call for cross-checking of altitude and distance.
"(But) the pilots weren't trained to do it," she said in an interview. "It happens. Sometimes it takes something like this to make people realize that there's a gap."
The report said the pilots likely delayed disconnecting the autopilot system because of the challenges they faced maintaining the visual cues from the airport.
Air Canada has already provided its pilots with more guidance on visual references, and it has issued explicit warnings on the limitations of the autopilot system in a certain mode. As well, Air Canada now requires instrument monitoring during all approaches when below a certain altitude, the TSB said.
In a statement released Thursday, Air Canada confirmed it has already made many changes, including upgrades to some Airbus aircraft, reaching out to other airports about improving runway lighting, and reviewing emergency response plans.
The board also found that when the crew requested the runway lights be adjusted to their maximum setting, that didn't happen because a tower controller was "preoccupied" with snowplows on the runway and an aircraft on a taxiway.
Fox said the lights, which can blind snowplow operators, are typically turned down a notch until an aircraft makes its final approach.
The Halifax International Airport Authority issued a statement Thursday saying it is reviewing the report, but it said officials wouldn't be commenting because of ongoing litigation.
Late last year, a Nova Scotia Supreme Court justice certified a class action lawsuit that names Transport Canada, Air Canada, the Halifax International Airport Authority, Nav Canada and Airbus SAS, the French company that built the jet.
Fox confirmed that the localizer beacon on Runway 05 has been replaced with a more advanced satellite-based system that provides suitably equipped aircraft with altitude and distance data. Other runways at the airport have long used a so-called Instrument Landing System, which also provides that information.
Meanwhile, the airport authority has also upgraded the approach lighting for Runway 05, reviewed its emergency response plan and upgraded its backup power, the TSB said.
After the crash, some passengers said they waited for more than an hour for emergency responders as they stood outside huddled against blowing snow and temperatures hovering around -6 C. The airport has said passengers waited up to 50 minutes for help and that firefighters were on scene within 90 seconds.
The TSB said recovery of the uninjured passengers was delayed by the severe weather and the failure of the airport's two standby generators. Without backup power, the airport's radio network failed, making it difficult to arrange for transportation after emergency responders declared the site clear for an evacuation.