The pilot of the helicopter that crashed near Los Angeles, killing nine people on board including NBA great Kobe Bryant, told air traffic controllers in his last radio message that he was climbing to avoid a cloud layer before plunging more than 1,000 feet (305 meters) into a hillside, an accident investigator said.
Radar indicated the helicopter reached a height of 2,300 feet (701 meters) on Sunday morning before descending, and the wreckage was found at 1,085 feet (331 meters), Jennifer Homendy of the National Transportation Safety Board (NTSB) said.
NTSB investigators went to the crash site in Calabasas on Monday to collect evidence.
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"The debris field is pretty extensive," Homendy said. "A piece of the tail is down the hill. The fuselage is on the other side of that hill. And then the main rotor is about 100 yards (91 meters) beyond that."
Some experts suggested the pilot might have gotten disoriented because of fog, but Homendy said investigating teams would look at everything from the pilot's history to the engines.
"We look at man, machine and the environment, and weather is just a small portion of that," she said.
"The pilot had asked for and received special clearance to fly in heavy fog just minutes before the crash and was flying at 1,400 feet (427 meters) when he went south and then west.
"The pilot then asked for air traffic controllers to provide flight following radar assistance but was told the craft was too low for that assistance.
"About four minutes later, the pilot advised they were climbing to avoid a cloud layer. When air traffic controllers asked what the pilot planned to do, there was no reply. Radar data indicates the helicopter climbed to 2,300 feet (701 meters) and then began a left descending turn. Last radar contact was around 9.45am."
Two minutes later, someone on the ground called 911 to report the crash.
Some experts raised questions of whether the helicopter should have even been flying. The weather was so foggy that the Los Angeles Police Department and the county sheriff's department had grounded their own choppers.
The Sikorsky S-76 killed the retired athlete along with his 13-year-old daughter Gianna and everyone else aboard, scattering debris over an area the size of a football field.
Crews recovered three bodies on Sunday and resumed the effort on Monday amid an outpouring of grief and shock around the world over the loss of the basketball great who helped lead the Los Angeles Lakers to five NBA titles during his dazzling 20-year career.
The pilot was identified as Ara Zobayan. He was the chief pilot for Island Express Helicopters, the aircraft's owner, the company said in a statement.
"Ara has been with the company for over 10 years and has over 8,000 flight hours," the company said, adding that it was working closely with the NTSB to investigate the crash.
"Zobayan was commercially certified as a pilot and certified as a flight instructor," Homendy said.
Several aviation experts said it is not uncommon for helicopter pilots to be given such permission, though some thought it unusual that it would be granted in airspace as busy as that over Los Angeles.
But Kurt Deetz, who flew for Bryant dozens of times in the same chopper that went down, said permission is often granted in the area.
"It happened all the time in the winter months in LA - you get fog," Deetz said.
The helicopter left Santa Ana in Orange County, south of Los Angeles, shortly after 9am, heading north and then west. Bryant was believed to be headed for his youth sports academy in nearby Thousand Oaks, which was holding a basketball tournament on Sunday in which Bryant's daughter, known as Gigi, was competing.
Air traffic controllers noted poor visibility around Burbank to the north and Van Nuys to the northwest. At one point, the controllers instructed the chopper to circle because of other planes in the area before proceeding.
The aircraft crashed about 30 miles (48 kilometers) northwest of downtown Los Angeles. When it struck the ground, it was flying at about 184 mph (296 kph) and descending at a rate of more than 4,000 feet per minute, according to data from Flightradar24.
Bryant had been known since his playing days for taking helicopters instead of braving the notoriously snarled Los Angeles traffic. "I'm not going into LA without the Mamba chopper," he joked on Jimmy Kimmel Live in 2018, referring to his own nickname, Black Mamba.
On Sunday, firefighters hiked in with medical equipment and hoses, and medical personnel rappelled to the site from a helicopter. About 20 investigators were on the site early on Monday. The Los Angeles County medical examiner, Dr. Jonathan Lucas, said it could take at least a couple of days to recover the remains.
Among those killed in the crash were John Altobelli, 56, longtime head coach of Southern California's Orange Coast College baseball team; his wife, Keri; and daughter, Alyssa, who played on the same basketball team as Bryant's daughter; and Christina Mauser, a girls' basketball coach at a Southern California elementary school.
Meanwhile, investigators in Los Angeles said on Tuesday that it was proving "very difficult" to recover the bodies and officially identify them at the scene of the helicopter crash.
Los Angeles County sheriff Alex Villanueva stated this was due to the "rugged terrain" of the hillside close to the Californian city.
Mr Villanueva said: "The coroner... started recovering human remains last night and they're continuing [that process] for the next several days.
"It's rugged terrain and it's a very steep hill. In fact, they had to bulldoze a road just to get a normal-size vehicle to the location, so it is very difficult."
Investigators from LA County coroner's office said they had recovered the first three bodies from the crash site and were searching for more remains.