The Associated Press

REDDING, Calif. — Witnesses of a fiery helicopter accident that killed nine people told investigators the aircraft had lifted off more slowly than normal before it struck a tree and crashed in a remote Northern California forest, officials said Friday.

After the chopper's nose hit the tree about 40 to 50 feet above ground, its rotor blades struck trees and branches before the aircraft plummeted to the ground Tuesday night, said National Transportation Safety Board member Kitty Higgins, citing accounts from 10 witnesses.

The aircraft came to rest on its left side about 150 yards from its takeoff site and then "quickly filled with very dense, thick black smoke" before igniting in a fiery blaze, Higgins said at a news conference in Redding, about 40 miles southeast of the crash site.

The Sikorsky S-61N was ferrying 10 firefighters, two pilots and a U.S. Forest Service employee back to base camp when it crashed in the Shasta-Trinity National Forest. Four of those aboard were rescued and taken to hospitals.

Investigators said Friday that they had recovered the cockpit voice recorder from the wreckage and that the device was bound for an NTSB laboratory in Washington.

It was unclear whether the recorder contained useful information, but it "is in better condition than we hoped, given the condition of the crash site," Higgins said.

Investigators plan to survey the treetop heights and topographical features of the crash site, take fuel samples, and review the aircraft's maintenance records.

They also plan to analyze the chopper's "escape windows, seat belts and other factors that would tell us something about the difficulties passengers would have had evacuating the aircraft," Higgins said.

Those killed included seven contract firefighters employed by Grayback Forestry Inc., one pilot who worked for Carson Helicopters Inc. and one U.S. Forest Service employee, who on Friday was identified as Jim Ramage, assigned to the agency's fire and aviation division.

Grayback on Friday released the name of its seventh employee killed in the crash, 21-year-old Steven Renno of Cave Junction, Ore., after locating his family at an Oregon campground.

Rick Charlson, whose son Scott Charlson was killed in the crash, said his son had called his parents in Eugene, Ore., the morning of the crash.

"He was excited," said Charlson, a salesman for a fertilizer and irrigation store. "He'd never been in a helicopter before. So he was really looking forward to that, too."

"We said all our 'I love yous, that was the end of every conversation," Charlson said Friday.

Authorities at the crash site worked to remove the victims' remains Friday.

Investigators plan to interview the survivors, three firefighters and a pilot, when they're "medically available," Higgins said.

Firefighters Michael Brown, 20, and Jonathan Frohreich, 18, were in good condition Friday morning at the University of California Davis Medical Center in Sacramento. Co-pilot Bill Coultas, 44, who suffered burns on about a third of his body, was in critical condition.

Firefighter Rick Schroeder, 42, was released from the hospital Friday after suffering a cracked shoulder and vertebra along with scratches, bruises and a badly cut lip.

The helicopter was made in 1964 and had more than 35,000 flight hours. One of its two engines had more than 1,000 hours and the other had about 200 hours. Carson Helicopters had owned the aircraft for about one year, Higgins said.

Reports indicate that there was clear visibility and "very light winds" up to 5 mph when the helicopter crashed.

The crew had taken its first flight of the day at 4:30 p.m. Tuesday. It had performed two water drops, completed two crew pickups and refueled before the accident at 7:45 p.m.

Investigators hope to complete their report on the accident in one year.

Hundreds of S-61s were built for military and civilian use. The helicopter has been in commercial service for more than 40 years and is one of the two models used to carry the president.

According to NTSB records, there have been 11 accidents involving civilian S-61s since 1983.

Investigators attributed one to "corrosion pitting" that caused a rotor to disintegrate in 1983 and another to a malfunction of an input freewheeling unit. The other crashes were blamed on pilot error, faulty maintenance or remained under investigation by foreign governments because they happened outside the U.S.

The Federal Aviation Administration reported another four accidents; two were blamed on mechanical failures.

In April, the FAA proposed a new "airworthiness directive" for S-61s, saying it was prompted by Sikorsky's "re-evaluation of the retirement life" for the main rotor shaft.

The proposed directive was "intended to prevent main rotor shaft structural failure, loss of power to the main rotor, and subsequent loss of control of the helicopter," the FAA said in announcing it.

The announcement included a public comment period, which ended on June 23; the agency is still weighing the proposed rule, said FAA spokesman Les Dorr.

Dorr said it was premature to speculate on whether the proposed directive had any connection to this week's crash.

Wayne Coulson, the CEO of Canada-based Coulson Group, said he has a fleet of five Sikorsky firefighting helicopters identical to one that crashed.

"We have a 110,000 safe flight hours on them. They're a superior aircraft," Coulson said.

Carson Helicopters "is a competitor of ours, a very safe company and a good competitor so it's very unusual that something like this happened," Coulson said in an interview with Associated Press Television News.