(Bloomberg) -- An international team of investigators is combing through the wreckage of the two aircraft that collided at Tokyo Haneda airport on Jan. 2 as they seek to establish what caused the runway incursion, with the voice and data recorders set to provide vital readouts of the fateful final moments before impact. 

The cockpit voice recorder from the smaller De Havilland Canada Dash 8 was recovered a day after the accident, and local media reported the flight recorder of the much larger Airbus SE A350 operated by Japan Airlines Co. was retrieved Thursday. The JAL plane will be cleared from the runway Friday morning so that operations can resume.

Airbus has dispatched experts to Japan to aid the investigation, and the teams have begun working on the mangled remains of the aircraft, which was almost entirely destroyed by a fire following the collision. 

Pressure is building to find out exactly what led to two aircraft ending up on the same runway strip at one of the world’s busiest commercial airports, and who should be held accountable. Initial readouts from conversations with air traffic control suggest the coast-guard plane didn’t have clearance for takeoff, while the Airbus A350 had permission to land. Yet the pilot of the smaller plane, the only person of a crew of six to survive the impact, has maintained he was cleared to depart. 

Airbus said after the crash that it had sent a team of specialists to assist the investigation. The French BEA accident investigation team is also involved, given the aircraft was manufactured in France, alongside the Japan Transport Safety Board.

It’s not unusual for the black boxes — which are in fact painted bright orange — to remain undiscovered for a while after a crash. While the Airbus A350 was largely intact even after impact with the coast-guard plane, the aircraft subsequently burnt out entirely, with the fire raging for more than six hours. That, in turn, may complicate any search effort inside the charred wreck, said Darren Straker, the former head of aircraft accident investigations for the United Arab Emirates.

“Finding it will not be immediate,” Straker said of the black-box devices. “They will know roughly where it is, but they will have to sift through it. When you’re going though a debris field everything looks the same, there’s evidence preservation issues.”

When China Eastern Airlines Co. Flight 5735 crashed in March of 2022, it took two days for the cockpit voice recorder to be located, and six days for the flight data box to be found. Still, the plane crashed into remote mountains and left a crater 20 meters (65 feet) deep. The flight data recorder was buried around 40 meters from the main crash site.  

Modern aircraft have two recorders: one for cockpit voices and other atmospherics, and one for flight data. Together, they provide the most comprehensive readout of an aircraft’s performance and that of the cockpit crew. The devices are heavily fortified to withstand severe impact, fire and extensive submersion. 

The US Federal Aviation Administration requires flight recorders to be able to survive at least an hour exposed to a fire of at least 2,000F (1,100C).

Black boxes have been retrieved and found to be usable in the past even after aircraft slammed into mountainsides at high speed, or after lying at the bottom of the ocean for several years. One of the longest hunts for black boxes occurred after the crash of Air France Flight AF447 in 2009 in the Atlantic. It took several years to locate the devices, and the readout helped piece together a fuller picture of what led to the accident that killed all 228 people on board. 

Investigators will seek to determine how the accident might have been avoided. Livestreamed footage appears to show the fueled-up coast guard Dash 8 lined up on the runway, and remaining stationary for around 47 seconds before it was struck by the Japan Airlines widebody jet. All 367 passengers and 12 crew members on Flight JL516 managed to escape the burning aircraft.

Transport ministry officials have revealed a transcribed flight recording that showed the coast guard plane did not have permission to enter the runway. Separately, stop-bar lights placed on the intersections onto the runway — which indicate whether the strip is clear or not — had been out of service since Dec. 27, though pilots had been made aware of the condition.

The pilot of JAL Flight 516 recalled seeing a “shadow” in their periphery moments before impact with the coast guard plane, JAL officials said Wednesday, citing interviews with crew members.

A spokesperson for JAL declined to comment on the investigation.

The Japan Safety Transport Board — a division of the Ministry of Land, Infrastructure, Transport and Tourism — will lead efforts to recover and examine the black boxes, JAL officials said.

“We will cooperate fully with the investigation to ensure this never happens again,” Transport Minister Tetsuo Saito told reporters.

(Adds reports of JAL flight recorder found in second paragraph.)

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