Associated Press

WASHINGTON (AP) -- The copilot of a helicopter ferrying firefighters implored "Fly darlin', fly darlin', fly darlin', fly darlin ...'" as the chopper lost power and fell out of the air in a rugged area of Northern California last year, according to a cockpit voice recording transcript released Wednesday. Nine of 13 people aboard were killed.

The transcript was among dozens of documents made public in the National Transportation Safety Board's investigation of the accident. The documents represent the facts gathered by investigators, but don't contain any conclusion on the cause of the Aug. 5, 2008 crash.

The Sikorsky S-61N had been airborne less than a minute when the chopper's main rotor lost power during takeoff. It hit trees and crashed into a remote mountainside in Shasta-Trinity National Forest.

The transcript indicates the pilots thought all was going well, but then suddenly the pilot in charge, Roark Schwanenberg, exclaimed: "Oh, God."

Copilot William Coultas swore and began pleading with the aircraft to regain power.

Schwanenberg was among those killed in the crash, one of the deadliest incidents involving firefighters in the U.S. in recent decades. Coultas was among four injured survivors.

The helicopter was carrying firefighters away from the front lines of a stubborn wildfire just before dusk. Worsening weather conditions forecast for the area prompted the decision to fly about 50 firefighters out of the Trinity Alps Wilderness.

The helicopter had completed two trips and just refueled before it picked up the third group and made the ill-fated takeoff. At the time of the accident, visibility was good enough that the pilots did not need to rely on instruments to make the flight.

Among the information undercovered by crash investigators is that there were several incidents prior to the crash of power fluctuations in or slow acceleration of General Electric CT58-140 engines of the type on the helicopter involved in the accident, according to one of the NTSB documents. The problem was traced to tiny bits of contamination lodged in an engine fuel control valve which caused the valve to bind or seize, the document said.

Earlier on the day of the crash, the Sikorsky attempted to land in another spot, but dust churned up by its rotors caused a "brownout" -- a condition in which visibility is limited by dust or sand -- and forced the helicopter to circle around before attempting another landing. Some of the chopper's mechanical workings recovered by investigators were covered with dust.

Copyright 2009 The Associated Press.

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