” Is there a problem? »Read the message from the air traffic controllers to the pilots.
The plane, with more than 500 people on board, was flying 1200 meters below its previous altitude and, indeed, there was a problem.
The front end of an engine had fallen, falling more than 7 miles towards freezing Greenland Ice Cap below.
The pilots were greeted with a handful of flashing lights, but did not grasp the extent of the problem until one of the flight attendants made it to the cockpit, according to a report into the incident from the French regulators.
They brought a phone from one of the passengers with a photo of the engine damage on it, easily visible from passenger windows on the right side of the cabin.
The plane, a Airbus A380, which was supposed to sail comfortably at 11,000 meters, made an emergency landing in Canada two hours later and no one was injured.
But regulators warned that the incident could have played out in a very different way if the debris from the explosion had struck the plane instead of plunging to the ground.
The ordeal put French authorities on a multi-year mission to find the lost engine parts and identify the root cause of the problem, forcing investigators to study miles of terrain made perilous by deep, invisible cracks in the ice cap. of Greenland and the constant threat of bear attacks.
This business was also hampered by months of inhospitable storms, limited daylight and poor visibility.
Researchers eventually discovered the key piece of debris – the motor fan – by accident, when a robot mapping glacial crevasses found itself rolling over where it had been buried nearly two years after it fell from the sky, Austin Lines, a company based in the United States. engineer who aided the recovery effort, said.
It was wrapped in four yards of snow and ice.
The search effort was crucial, authorities revealed last month.
Study of the recovered debris showed that the engine was not damaged during maintenance, as investigators initially predicted.
Rather, the problem appeared to be with the weakness of the metal used to create the engine’s giant front fan – indicating that what initially appeared to be a freak accident may not have been an isolated incident, according to a report. September from France. Civil aviation safety investigation and analysis office (BEA) who conducted the investigation.
Engine makers have already worked to fix the problem, but the BEA is now calling on regulators in the United States and Europe to take a closer look at how aircraft engines are designed, manufactured and certified for flight – in hoping that closer examination can eliminate flaws before they arise.
In-flight engine failure remains extremely rare, according to US and European authorities.
But the unexpected findings of the BEA investigation highlight just how critical an excruciating 21-month search for a lost engine part was to understanding how to prevent the same disaster from happening twice.
In search of the Greenland tundra
The day after the Air France flight in 2017, BEA investigators and representatives of aircraft and engine manufacturers, including Airbus, General Electric and Pratt & Whitney, gathered at the Canadian airport to monitor the damage. to the plane.
“It was determined early in the investigation that the recovery of the missing parts and in particular the fragments of the fan hub, was essential to establish the circumstances and the factors explaining this accident”, according to the BEA report.
Investigators looked at data from the aircraft’s flight data recorder – or “black box” – to determine exactly when the explosion occurred and determined that the debris likely landed about 97 kilometers from Narsarsuaq in southwest Greenland.
Within days, helicopters were dispatched and investigators scoured the pure white landscape for signs of the great fan.
But after a week and three unsuccessful search flights, the ground was already buried under new layers of snow.
With harsh winter months ahead, investigators decided to resume their research the following spring.
They would use planes equipped with Synthetic Aperture Radar (SAR) – the same type of radar used to create 3D maps of the Earth – that would attempt to search for unseen objects beneath the surface of the ice caps.
A team of investigators would also join the effort on foot, using ground-penetrating radar, a device that resembles a lawn mower and is commonly used by archaeologists to search for buried objects.
They focused on places that airborne radars believe could be the resting place for engine debris while preparing for freezing temperatures and avoiding large cracks often hidden in ice caps called crevasses.
But those two initial efforts failed, in part because the radars weren’t looking deep enough below the icy surface.
With another brutal winter approaching, the search was once again suspended.
Mr Lines told CNN Business that at one point investigators threw a replica of the engine fan in the snow, just to make sure the radars they were using for the search could accurately detect the metal. buried.
But they couldn’t. And for months, aftershock debris was also lost.
The French research laboratory of Onera, which was behind the effort to use SAR radar on planes to locate debris, also found that the data collected was too muddled – or “noisy” in engineering terms – and the Onera team spent months developing new analytical methods. information before ultimately narrowing the search box to a handful of possible locations, according to the BEA report.
Mr Lines, who developed a four-wheeled robot called FrostyBoy designed to map crevices, was approached by the BEA to help with the recovery effort – but the robot ended up being the backbone of the entire project. .
While searching for cracks, the rover’s sensors picked up an abnormal reading, revealing that the robot had – by sheer chance – rolled over to the exact resting place of the engine fan.
“We are ridiculously lucky that it turned out the way it did,” Mr. Lines said of FrostyBoy’s random detection.
This gave his robot, a project he worked on while pursuing his doctorate at Dartmouth, a small but bizarre claim to fame.
“I don’t think anyone would care much if a bunch of guys went out with a robot and didn’t do much with it,” he joked.
In fact, recovering the Fan Hub Shard presented its own set of issues, however.
He was buried less than six meters from a four-meter-wide crevasse that could have reached hundreds of meters deep, according to BEA documents.
In June last year, a team of five, including Mr Lines and a team of Icelandic mountain guides, traveled by helicopter to the excavation site.
A small, dome-shaped tent built to withstand the high winds sheltered them during their three-day excavation effort.
At night, they slept with guns next to their sleeping bags – a precaution for a polar bear attack.
The hidden crevices posed the constant risk of the ground beneath the crew’s feet collapsing, and they used metal rods to check the depth of the ice before stepping into new territory.
An invisible crevasse might even have been hidden under the excavation site, so they wore harnesses with ropes tying them to a nearby anchor point while they shoveled snow.
Mr. Lines, who had previously helped extract the replica motor fan from the ice cap, was the only member of the five-crew recovery team to participate in this effort and knew how grueling the job would be.
The first few feet of snow and ice above the engine’s fan unrolled easily, but Mr. Lines used a chainsaw to cut through the thick layers of frost compacted below.
The crew dug a ramp into the excavation site so that a sled operated by a pulley system could be used to haul approximately 20 metric tons of snow out of the pit.
“We had a lot of sun because the sun doesn’t really go down [that time of year]Mr. Lines said.
“So we just worked all night, then we went to bed for a few hours, and then we woke up and just started digging again.
Finally, on the third day, the tips of the engine fan blades appeared.
An industrial heater was used to melt the ice away from the fan before the makeshift pulley system carried it to surface level.
In footage of the excavation captured by the team, Mr. Lines and the rest of the crew scream and clap as a helicopter lifts the giant fan fragment, which was mutilated and slightly deformed by the blast of 2017 but still largely intact.
The battered piece of debris subsequently proved crucial to understanding what was wrong with the 2017 Air France flight.
Investigators determined this was not a maintenance issue, as previously thought.
The engine actually failed due to a phenomenon called “cold fatigue,” which caused the metal in the engine fan to fail much sooner than expected.
Part of the problem could be that jet engine designers did not fully understand the limitations and weaknesses of the type of titanium – called Ti-6-4 – used in this engine.
The material is also widely used in the aerospace industry.
Indeed, according to the BEA final report, “the mechanisms at the origin of the initiation of a fatigue crack by cold contact were still not completely understood at the time of the accident and are still not. today “.