On a cold March night in 2015, as most of Halifax slept, a routine passenger flight was making its final approach to the city’s international airport. For the 138 souls onboard, what should have been an ordinary landing would become anything but.

All of a sudden, something goes terribly wrong. The aircraft strikes power lines, plunging the airport into darkness.

This is the story of Air Canada Flight 624.

It’s the 29th of March, 2015. At Toronto’s Pearson International Airport, the crew of an Airbus A320 prepare for a routine two-hour flight to Halifax. The aircraft, a reliable workhorse of Air Canada’s fleet, has served faithfully for almost 24 years.

In the cockpit sits an experienced crew – in the left seat, the captain with nearly twelve thousand flight hours, including over 5,500 on the A320, with around 1,200 in command. The captain, who had been diagnosed with obstructive sleep apnea in 2009, had been working evening shifts in the days leading up to this flight.

In the right hand seat, the first officer had over eleven thousand flight hours, around 6,000 of which were on the A320. For this trip, the captain will act as pilot flying and the first officer will be pilot monitoring.

As fate would have it, this would be the first time this particular pairing of pilots had flown together.

The weather forecast for their Halifax destination was concerning: winds at 15 knots gusting to 21 from the north, visibility just half a mile in moderate snow. The temperature was a chilly -5 degrees Celsius or 23 degrees Fahrenheit. While challenging, these conditions still fall within Air Canada’s operational limits – barely.

But besides the weather, the airport at Halifax has its own unique challenges. More on this later.

In Halifax, winter storms are a fact of life. But tonight’s combination of heavy snow, gusty winds, and a basic runway lighting system dating back to simpler times would create conditions that would test even this very experienced crew.

While these challenges would later prove critical, for now, the 138 people aboard – 133 passengers and a reduced cabin crew of just three instead of the usual four – settled in for their flight. Transport Canada had recently brought in a rule allowing one flight attendant per 50 passengers instead of the previous 1:40 bringing it into line with U.S. and E.U. standards.

This reduced cabin crew ratio of 1:50 meant flight attendants would need to manage multiple emergency exits, requiring special dual-exit training. Though Transport Canada mandated this training, airlines like Air Canada were allowed to implement the new crew ratio before actually providing the new training. And at the time of this flight, none of the cabin crew had received this required dual-exit training, nor were they aware that such training was needed.

At 10:05 PM, as Flight 624 climbed into the dark winter sky over Toronto, the real work was just beginning. While passengers settled in for the short journey east, the pilots were already planning for contingencies. They discussed amending their alternate airport from Montreal to Moncton. This change would allow more time to hold at Halifax if landing were delayed due to weather.

The aircraft climbed normally and levelled off at cruise altitude.

As part of their approach planning, the crew meticulously calculated cold temperature corrections for the Halifax approach. The final approach fix – that critical point where aircraft transition to their final descent – would require precise crossing altitudes.

So why do the crew need to concern themselves with cold temperature corrections? In severe cold like tonight’s, an aircraft’s altimeter plays tricks, reading higher than the true altitude – a deceptively dangerous error that grows larger the closer you get to the ground. Even their minimum descent altitude, that last safe height without visual reference to the runway, would need careful adjustment. As the pilots worked through their calculations, the dark night held no hints of how significant these numbers would soon become.

Meanwhile, far below their cruising altitude of flight level three five zero or 35,000 feet, a winter storm continued to build over their destination.

But this was only the beginning of their concerns. Unlike most major runways, Halifax’s Runway 05 has only basic lighting extending 1,500 feet from the threshold – an ODAL (Omnidirectional Approach Lighting) system with just five individual lights spaced 300 feet apart. In the United States, this runway wouldn’t even qualify for an approach in these conditions without an additional 900 feet of approach lighting.

Ahead of the crew lies an approach with some hidden dangers yet to reveal themselves. The runway’s upward slope creates treacherous visual illusions. And a previously undiscovered panel setup error means setting the runway lights to “setting 4” automatically reduces the approach lights to a much dimmer “setting 2” – a crucial flaw that will soon come into play.

And at the opposite end of the airport, visibility sensors record wild fluctuations – from 1,600 to 4,000 feet of visibility within fifteen-minute spans. Somehow, the flight crew don’t get informed about these pertinent readings taken at the runway’s midpoint.

Not only that, but even the Precision Approach Path Indicator lights (known as PAPI) are operating at reduced power, having been at this setting since the previous morning. PAPI lights are important visual aids for pilots no matter what the weather. The system consists of four lights alongside the runway showing white if too high and red if too low helping pilots confirm they’re on the correct glidepath during approach with 2 white and 2 red lights indicating perfect positioning along the glidepath.

At their destination in Halifax, conditions are deteriorating. Snow ploughs are at work to keep the runway clear. Given the weather situation, the flight crew makes a tactical decision to hold at a point called CETTY, knowing they have enough fuel to wait until 1:00 AM for conditions to improve. But, the question loomed, would improved weather conditions arrive in time?

At 11:34 PM, Flight 624 enters its holding pattern. As they continue circling in the darkness over Halifax, just after midnight, there’s a shift change of air traffic controllers at the tower. The crew had earlier put in a request for maximum intensity runway lights, but somehow, this request wasn’t actioned. And that’s a detail that will soon prove critical.

For the crew, the precision required tonight leaves no room for error. They methodically calculate their approach: a 3.5-degree descent angle, adjusted up from the published 3.08 degrees to account for altimeter-deceiving temperatures. Their final approach fix: 2,200 feet, factoring in a 200-foot cold weather adjustment. The minimum descent altitude: 813 feet, carefully built from the published 740 feet plus essential safety buffers. Remember, the pilots are making all these precise calculations because cold air can make their altimeters read higher than their actual height, which could be potentially dangerous.

At 12:09 AM, the tower reports visibility of one-eighth of a mile then quickly updates that to one-quarter mile. By 12:13 AM, they’re reporting an improved half a mile visibility in falling and drifting snow.

And based on this apparent improvement, the flight crew determines they can proceed with the approach. After all, they’ve got enough fuel to hold if needed.

At this point, it’s likely the crew were falling prey to a psychological condition known as “plan continuation bias.” We’ll come back to this later.

It’s now 12:16 AM and air traffic control clears Flight 624 to a point called ODKAS, eleven nautical miles from the runway, authorizing their descent to 4,000 feet. The snowfall intensifies as they descend into darkness, snowflakes hammering against the windscreen like static, further isolating the crew from the world outside.

At 12:23 AM, twelve nautical miles from the runway threshold, the aircraft levels out at 3,400 feet. The pilots initiate a left turn to intercept the localizer at eleven miles out, their eyes most likely alternating between instruments and the snow-filled void ahead hoping to catch a glimpse of any form of ground reference.

Three minutes later, at 12:26 AM, about eight miles from the runway threshold, the captain calls for the landing gear to be extended. The landing lights remain off a technique pilots use to reduce the disorienting effect of snow reflecting in their vision. At 6.7 nautical miles out from the runway threshold, the aircraft is precisely where it should be gear down, flaps set, fully configured for landing.

Through the swirling snow, the aircraft begins its descent. But something isn’t quite right. The crew has unknowingly started down just moments too soon – 0.2 nautical miles before the proper final approach fix. In aviation’s unforgiving mathematics, this seemingly tiny deviation would prove, let’s just say, “problematic”.

The winter winds aren’t helping either. Like invisible hands, persistent gusts keep nudging the aircraft away from its intended path. The Airbus A320’s autopilot, faithful to its programming but blind to the bigger picture, keeps maintaining its assigned 3.5-degree angle. When these gusts push the aircraft lower, the autopilot dutifully maintains that same angle – creating a path that mirrors the intended one, but further below it. And in the darkness below, the snow-covered ground is getting closer.

To make matters worse, the crew did NOT monitor the vertical component of their approach. But this wasn’t pilot error – they were dutifully following Air Canada’s standard procedures at the time.

Without this monitoring and without manual corrections, this deviation would only increase. It’s a bit like following a straight line that’s too low while thinking you’re on the right path, and nobody’s checking to make sure the plane is at the correct height.

Unbeknownst to the pilots, they’re now getting dangerously close to the ground.

Meanwhile, in the cabin, the passengers were probably blissfully unaware that anything was out of the ordinary. They likely couldn’t see much out of their windows, but wouldn’t have expected to either given it was dark and snowy outside. Their descent would have felt just like any other descent they were accustomed to.

12:29 AM and the synthetic voice of the radio altimeter calls out “Four hundred.” Almost immediately after, they cross their calculated minimum descent altitude at 1.2 miles out from the runway threshold.

“Minimum, lights only,” calls the first officer, straining to make sense of what can be seen out the window, or, what can’t be seen to put it more accurately. The captain responds with “Landing,” reporting visual contact with some approach lights.

The fact they can only see lights, combined with their unnoticed descent below the proper approach path, is setting up a dangerous situation where they have minimal visual references but are continuing the approach anyway.

By their own company’s procedures, seeing even one of ten specific visual references is enough for them to continue. Included among these specifically named visual references are:

the runway or runway markings
threshold or threshold markings
approach lights, or,
the runway edge or centerline lights

But there’s a catch they haven’t yet realized: they’ve already passed below the published minimum descent altitude, significantly farther back from the runway than they should be.

Under normal conditions, a runway’s lights tell a story to approaching pilots. The spacing between edge lights, their relationship to the threshold lights – it’s a precise visual language that speaks of height, distance, and position. But tonight, unfortunately for the pilots, nature has scrambled that language. That upward slope adds another layer of danger even a subtle incline can trick pilots into thinking they’re higher than they actually are.

The heavy snowfall acts like a veil, allowing the crew to see only fragments of the runway’s light pattern at a time. In this swirling white void, each snowflake, caught in what little light there is, helps to dissolve the pilots’ depth perception. Movement becomes impossible to judge. The human brain, struggling to interpret this broken visual dialogue, can no longer trust what it sees.

Yet through all this, the autopilot remains engaged – well beyond the point where pilots would normally take manual control. It’s a decision that speaks to a profound trust in automation, but one that will prove costly in these final moments.

Back in the cabin, the passengers and cabin crew likely believed they were just moments away from a regular landing. Little do they know what’s about to happen.

At 12:29 am and 47 seconds, the captain finally disconnects the autopilot, taking manual control. The radio altimeter counts down with mechanical precision:

“One hundred.” “Fifty.”

Suddenly, the first officer’s voice cuts through the darkness: “Pull up!”

But it’s too late. Power lines snap. The airport plunges into darkness. 740 feet short of the runway. The captain reacts instantly. Full power. Maximum nose-up. A textbook go-around initiation. Unfortunately, they were out of time.

12:30 am exactly. A left tire catches an approach light. Then impact. The landing gear slams into the snow-covered embankment. Violently. The aircraft hits the localizer antenna array, becomes airborne again, strikes the ground again. And again.

Darkness fills the cabin as all power cuts out. In the cockpit, both pilots’ harnesses fail. The captain’s head strikes the glare shield. The first officer’s eye is seriously injured.

The fuselage crumples. Nose gear collapses. Landing gear tears free, becoming deadly projectiles. They rip through the horizontal stabilizers. A cargo beam punches through the cabin floor. A coffee maker from the galley breaks loose, striking a flight attendant. And in the darkness of the powerless cabin, the PA system falls silent.

The evacuation must begin. Without announcements. Without lights. Without power.

Passengers initiate their own evacuation through four overwing exits, stepping into the very cold Halifax night, many of them in very light clothing like shorts, t-shirts and open-toed shoes obviously more suitable for much warmer weather. Some passengers also brought their carry-on baggage despite being told not to. Emergency services arrive quickly but face challenges evacuating people in dark, snowy conditions.

Miraculously, there were no lives lost. Many of the injuries were consistent with passengers not being in the brace position, as no emergency was expected and there simply wasn’t time to prepare. There was one serious injury, twenty-four minor injuries, and amazingly, 113 uninjured – numbers that clearly mask how incredibly close they came to total catastrophe.

Following a detailed investigation, the probable cause was the flight crew’s continuation of an unstable approach in deteriorating weather conditions. Multiple critical factors emerged that contributed to this outcome.

At the heart of the accident was a systemic issue: Air Canada’s procedures didn’t require crews to track their altitude and distance from threshold after passing the final approach fix a procedure that contradicted both Air Canada’s and Airbus’s own manuals. This significant oversight went unnoticed by Transport Canada, the regulatory body responsible for reviewing and approving Air Canada’s Aircraft Operating Manual and Standard Operating Procedures.

The pilots, while following their company’s procedures, never detected they had drifted below the planned descent profile. The flight path angle guidance mode wasn’t providing true vertical guidance it was simply maintaining an angle in 3D space, exactly what it was designed to do.

The situation was further compromised by the airport’s lighting system settings. When the crew requested maximum runway lighting (setting 5), they instead received setting 4, which provided only 25% of the maximum brightness. Even worse, this automatically reduced the approach lights to setting 2, making them less than one-third as bright as they could have been. In these challenging weather conditions, this significant reduction in lighting would have made it extremely difficult for the crew to visually judge their position relative to the runway.

Plan continuation bias that deep-seated human tendency to stick with the original plan even when conditions change emerged as a significant contributing factor. This psychological factor delayed the crew’s recognition that something was wrong, and by the time they initiated a go-around, it was already too late.

Regarding the captain, who was earlier diagnosed with sleep apnea, the report found no evidence that fatigue played a causal role in this accident.

We study accidents like these so aviation can become even safer. In the aftermath of Flight 624, Air Canada revised its flight operations procedures and pilot training, Halifax International Airport Authority upgraded its runway lighting systems, and NAV CANADA issued new directives regarding runway lighting settings.

📄 SOURCES Final report: https://finalreports.net/2015/air-canada-flight-624-final-report.pdf