Four hours after an Air France flight in September 2017 Paris to The angel, one of the aircraft’s four engines exploded spontaneously.
“Is there a problem?” Read the message from air traffic controllers to the pilots.
The aircraft, with over 500 people on board, was flying 1,200 meters below its previous altitude, and indeed there was a problem.
The front part of an engine fell off and fell more than seven miles in the frozen direction Greenland Ice Sheet below.
The pilots were greeted by a couple of flashing warning lights, but they didn’t understand the scope of the problem until one of the flight attendants walked into the cockpit, according to a report from French regulators about the incident.
They brought a phone from one of the passengers and it had a photo of the engine failure that was clearly visible from the passenger windows on the right side of the cabin.
The plane, a Airbus A380, which was supposed to travel comfortably at 11,000 meters, landed two hours later in an emergency in Canada and nobody was injured.
However, regulators warned that the incident could have been different if debris from the explosion had hit the plane instead of falling to the ground.
The ordeal put the French authorities on a year-long mission to find the lost engine parts and pinpoint the root cause of the problem. Investigators had to investigate miles of areas made dangerous by deep, invisible cracks in the Greenland ice sheet and the constant threat of polarity bear attacks.
The endeavor was also hampered by months of inhospitable storms, limited daylight, and poor visibility.
The researchers finally found the key piece of the debris by accident – the engine’s fan – when a crevasse-mapped robot rolled over the spot where it was buried almost two years after it fell from the sky, Austin Lines, an American A citizen engineer who assisted the restoration effort said.
It was packed in four feet of snow and ice.
The excavation efforts proved crucial, the authorities said last month.
Examination of the salvaged debris revealed that the engine was not damaged during maintenance, as investigators originally predicted.
Rather, the problem appeared to be related to the weakness of the metal used to make the engine’s giant front fan – which may not have been considered an isolated case, according to a September report from France Office for Investigation and Analysis of Civil Aviation Security (BEA), who led the investigation.
Engine manufacturers have already worked to address the problem, but the BEA is now urging regulators in the US and Europe to dig deeper into the design, manufacture and certification of aircraft engines for flight – in the hope that a more precise one Examination of this problem can resolve defects before they occur.
According to the US and European authorities, engine failures during the flight are still extremely rare.
However, the unexpected conclusions from the BEA’s investigation show that an agonizing 21 months’ search for a lost engine part was key to understanding how to prevent the same disaster from happening twice.
Search Greenland’s tundra
The day after the Air France 2017 flight, BEA investigators and representatives from aircraft and engine manufacturers, including Airbus, General Electric and Pratt & Whitney, gathered at the Canadian airport to investigate the damage to the aircraft.
“It was determined quite early in the investigation that the restoration of the missing parts, and particularly the fragments of the fan hub, is essential in determining the circumstances and factors that explain this accident,” the BEA report said.
Investigators examined the data in the aircraft’s flight recorder – or “black box” – to find out exactly when the explosion took place and determined that the debris landed probably about 97 kilometers from Narsarsuaq in southwest Greenland.
Within a few days, helicopters were dispatched and investigators searched the pure white landscape for signs of the large fan.
But after a week and three unsuccessful search flights, the area was already buried in fresh layers of snow.
Given the months of harsh winter weather, investigators decided to continue their search the following spring.
They would use aircraft equipped with synthetic aperture radar (SAR) – the same type of radar used to create 3D maps of the earth – that would try to search for invisible objects beneath the surface of the ice sheet.
A team of investigators would also join the effort on foot and deploy ground penetrating radar, a device that looks like a lawn mower and is commonly used by archaeologists looking for buried artifacts.
They focused on places where the airborne radars may be the resting place of engine debris as they brace themselves against the freezing temperatures and dodge large and often hidden cracks in the ice sheets called crevasses.
Both initial efforts failed, however, in part because the radars did not search deep enough under the icy surface.
The search was interrupted again with another brutal winter.
Lines told CNN Business that investigators once threw a replica of the engine fan in the snow to make sure the radars they used to search could accurately spot the buried metal.
But they couldn’t. And the replica debris was lost for months.
The French Onera research laboratory, which was behind the effort to use SAR radar on planes to find the debris, also found that the data it collected was too chaotic – or technically “noisy” – and the Onera team For months, developed new analysis methods for the information before the search field is finally narrowed down to a handful of possible locations, according to the BEA report.
Mr Lines, who developed a four-wheeled robot called FrostyBoy that was designed to map crevasses, was used by the BEA to aid in the recovery effort – but the robot was the linchpin of the whole project.
While looking for cracks, the rover’s sensors detected an abnormal reading and determined that the robot had accidentally rolled over the exact resting place of the engine fan.
“We’re ridiculously happy that it happened the way it did,” Lines said of FrostyBoy’s accidental detection.
It gave his robot, a project he was working on during his PhD in Dartmouth, a small but bizarre claim to fame.
“I don’t think anyone would care that much if some guys went out with a robot and didn’t do much with it,” he joked.
However, actually getting the Fan Hub fragment came with its own problems.
It was buried less than six meters from a four meter wide crevasse that, according to BEA documents, could have been hundreds of meters deep.
Last June, a team of five, including Mr Lines and a team of Icelandic mountain guides, flew to the excavation site by helicopter.
A small dome-shaped tent designed to withstand the strong winds protected them during their three days of excavation.
At night, they slept with guns next to their sleeping bags – a precautionary measure for a polar bear attack.
Hidden crevasses presented the constant risk of the ground collapsing beneath the crew’s feet, and they used metal rods to check the ice depth before breaking new ground.
An invisible crevasse could even have been hidden under the excavation site, so they wore belts with ropes that they attached to a nearby anchor point while they shoveled snow.
Mr. Lines, who had previously helped dig the replica of the engine fan out of the ice sheet, was the only member of the five-man salvage crew who had been part of the effort and knew how strenuous the work would be.
The first few feet of snow and ice above the engine fan shoveled out easily, but Mr. Lines used a chainsaw to hack apart the thick, compacted layers of frost below.
The crew carved a ramp into the excavation site so that about 20 tons of snow could be smuggled out of the pit with a sled operated by a pulley system.
“We had a lot of sunshine because the sun doesn’t really set [that time of year]”Said Mr. Lines.
“So we just worked through the night and then went to bed for a few hours and then woke up and just started digging again.”
On the third day, the tips of the engine’s fan blades finally came into view.
An industrial heater was used to melt ice away from the fan before the makeshift pulley system pulled it out at surface level.
In footage of the excavations recorded by the team, Mr. Lines and the rest of the crew lift the huge fan fragment that was maimed and slightly warped by the 2017 explosion, but is still largely intact.
The battered chunk of debris later proved crucial in understanding what actually went wrong on the 2017 Air France flight.
Investigators determined that it was not a maintenance issue as previously believed.
The engine actually failed due to a phenomenon known as “cold lingering fatigue,” which caused the metal in the engine fan to fail much earlier than expected.
Part of the problem could be due to the fact that engine designers did not fully understand the limitations and weaknesses of the type of titanium used in this engine – called Ti-6-4.
The material is also extremely common in the aerospace industry.
According to the final BEA report, “The mechanisms that triggered the onset of indwelling cold-dwelling fatigue cracks were not fully understood at the time of the accident and are still unknown to this day.”
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