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The helicopter carrying Kobe Bryant and eight other passengers that crashed into a hillside on Sunday in Calabasas, California, reached a climbing height of 2,300 feet before it dove to the ground, an accident investigator said.

Jennifer Homendy of the National Transportation Safety Board said Monday that the pilot of the helicopter told air traffic controllers in his last radio message that he was climbing to avoid a cloud layer. Then the helicopter plunged more than 1,000 feet into a hillside. NTSB investigators arrived on the scene Monday.

"The debris field is pretty extensive," Homendy said.

"A piece of the tail is down the hill," she said. "The fuselage is on the other side of that hill. And then the main rotor is about 100 yards beyond that."

The pilot was identified as Ara Zobayan, 50, who was among those killed in the crash.

The helicopter did not have a black box, and the recording device was not required for the aircraft, NTSB investigators said Monday afternoon. The NTSB also said it recovered an iPad that might have information from the flight.

Some experts suggested that the pilot might have become disoriented because of fog. Homendy said investigating teams would look at everything, from the pilot's history to the helicopter's engines.

"We look at man, machine and the environment," she said. "And weather is just a small portion of that."

The pilot 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, Homendy said.

The chopper went down in Calabasas, about 30 miles northwest of downtown Los Angeles, after departing John Wayne Airport in Orange County at 9:06 a.m. PT. The first 911 call reporting the crash was received at 9:47 a.m.

Audio reviewed by ESPN indicated that, a few minutes before the crash, an air traffic controller told Zobayan that he was "still too low level for flight following," meaning the aircraft was below the level at which it could be picked up by radar due to the area's hilly terrain. That audio came from recordings posted on LiveATC.net, which has partial audio of the communication between the pilot and air traffic controllers.

Additional recordings between Zobayan and air traffic controllers posted on the site indicate that the pilot was getting guidance from controllers as he navigated what was reported to be dense morning fog.

Air traffic controllers noted poor visibility around Burbank, to the north, and Van Nuys, to the northwest. After holding up the helicopter for other aircraft, the controllers cleared the Sikorsky S-76 to proceed north along Interstate 5 through Burbank before turning west to follow U.S. Route 101, the Ventura Freeway.

Shortly after 9:40 a.m., the helicopter turned again, toward the southeast, and climbed to more than 2,000 feet above sea level. It then descended and crashed into a hillside at about 1,400 feet, according to data from Flightradar24.

When it struck the ground, the helicopter was flying at about 160 knots (184 mph) and descending at a rate of more than 4,000 feet per minute (45 mph), the Flightradar24 data showed.

Authorities said nine people were aboard the helicopter and presumed dead. Bryant, a basketball great who spent his entire 20-year career with the Los Angeles Lakers, was among the victims. Bryant's 13-year-old daughter, Gianna, also was killed, a source told ESPN.

The National Transportation Safety Board sent a team of investigators to the site. The NTSB typically issues a preliminary report within about 10 days of a crash that gives a rough summary of what investigators have learned. A ruling on the cause of an aviation crash can take a year or more.

Zobayan was certified to fly commercial helicopters and had no record of accidents, incidents or enforcement actions with the Federal Aviation Administration.

An FAA aircraft-registration database showed that the helicopter was a 1991 Sikorsky S-76B model owned by a company named Island Express Holding Corp. It was previously owned by the state of Illinois, according to the database.

"The S-76 is a pretty expensive, sophisticated helicopter. ... It's certainly a quality helicopter," said Justin Green, an aviation attorney in New York who flew helicopters in the Marine Corps.

On Sunday morning, Colin Storm was in his living room in Calabasas when he heard what sounded to him like a low-flying airplane or helicopter.

"It was very foggy, so we couldn't see anything," he said. "But then we heard some sputtering and then a boom."

Storm could see smoke rising from the hillside in front of his home.

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Firefighters hiked in with medical equipment and hoses, and medical personnel rappelled to the site from a helicopter but found no survivors, Los Angeles County Fire Chief Daryl Osby said.

Firefighters worked to douse flames that spread through about a quarter-acre of dry brush, Osby said.

Los Angeles Police Department spokesman Josh Rubenstein said the department's Air Support Division grounded its helicopters Sunday morning due to foggy conditions and didn't fly until later in the afternoon.

"The weather situation did not meet our minimum standards for flying," Rubenstein said, adding that the fog "was enough that we were not flying."

LAPD's flight minimums are 2 miles of visibility and an 800-foot cloud ceiling, he said. The department typically flies two helicopters when conditions allow, one in the San Fernando Valley and one in the L.A. basin, he said.

The LAPD Air Support Division is the largest municipal airborne law enforcement organization in the United States, according to the department.

The Associated Press contributed to this report.