The National Transportation Safety Board (NTSB) has made public the factual report and supporting material involving the Aug. 5, 2008 fatal crash of a Sikorsky S-61N (N612AZ) in Weaverville, CA.

The crash resulted in the deaths of seven firefighters and two crewmembers. The copilot and three firefighters received serious injuries when the helicopter crashed at an elevation of around 6,000 feet in the mountains. The U.S. Forest Service was operating the S-61N, which was registered to Carson Helicopters of Grants Pass, OR.

The preliminary accident report said the S-61N experienced a loss of power to the main rotor during takeoff initial climb, and subsequently impacted trees and terrain. Post- impact fire destroyed the helicopter.

Visual meteorological conditions prevailed for the cross-country flight that was originating at the time of the accident. A company visual flight rules (VFR) flight plan had been filed. The helicopter was departing from Helispot 44 (H-44, elevation 5,935 feet) en route to Helispot 36 (H-36, elevation 2,516 feet) when the accident occurred.

The helicopter had been assigned to transport approximately 50 wild land firefighter helitack crewmembers out of the Trinity Alps Wilderness of the Shasta Trinity National Forest due to forecasted worsening weather conditions. The helicopter had completed two trips, and had gone to Trinity Helibase to refuel. After it had refueled, it returned to H- 44 for its third load of passengers. During departure, the helicopter impacted trees and subsequently terrain, coming to rest on its left side. A post-crash fire consumed the aircraft.

The factual report states:

After the pilots were notified of the manifested weight of the firefighters and cargo, the co-pilot stated that the performance load calculation numbers indicated a maximum payload at 2,552 lbs at 32 degreesC. He added that because the temperature was 12 to 13 degrees cooler and their payload was 200 lbs less, the helicopter would be able to perform.

Both pilots restated that they were indeed 200 lbs lighter than the previously calculated weight and the copilot affirmed that the helicopter was "good to go." At no time in the CVR recording do the pilots discuss the fact that the engine reached topping on the previous two departures from H-44.

The PIC began to increase the collective for takeoff and the co-pilot was verbally informing the pilot that the helicopter was clear from the trees to the right. The copilot stated "okay, just nice and smooth here," and he called out the engine torque was increasing through 75 percent torque to 80, and then to 85. About four seconds later he called out 90 percent [torque] and then 103 percent. About nine seconds later he informed the PIC that NR had decreased to 100 percent and was drooping. The recording ended 20 seconds later.

The sound-spectrum analysis of the CVR recordings indicated that the engines reached topping 20 seconds after departure, with an NG of 102.1-percent and 101.5 percent on the individual engines until the end of the recording. During this time, the NR began a slow droop from 106.6-percent to 91-percent over 60 seconds.

Witnesses stated that as the helicopter began to lift off, the vertical ascent appeared very slow and the helicopter moved as though it was labored. The helicopter began to move forward in a nose-low configuration, and was drifting right with the nose still pointing in the same direction. The flight path of the helicopter continued forward and then began losing altitude as it continued down slope. The helicopter collided with the trees and subsequently impacted the down sloping terrain, coming to rest on its left side.