Several established federal criminal investigations are under way into the events surrounding the August 2008 helispot takeoff crash of a Carson Helicopters Sikorsky S-61N operating under contract to the U.S. Forest Service that killed nine near Weaverville, Calif. The pilot, a U.S. Forest Service check airman, and seven firefighters were killed; the copilot and three firefighters survived.
Last month the NTSB found that the crash's probable cause was Carson's intentional understatement of the helicopter's empty weight; alteration of the power-available chart to exaggerate the helicopter's lift capability; practice of using unapproved, above-minimum specification torque in performance calculations that, collectively, resulted in the pilots' relying on performance calculations that significantly overestimated the helicopter's load-carrying capacity and did not provide an adequate performance margin for a successful takeoff; and insufficient oversight by the U.S. Forest Service (USFS) and the FAA.
The NTSB said contributory crash factors included the flight crew's failure to note the helicopter's approach to maximum performance (engine topping) from the same helispot on two previous takeoffs "because they were accustomed to operating at the limits of the helicopter's performance." It also noted the role of the helicopter's non-crash-resistant fuel tanks in the intense post-crash fire, non-crash-resistant seats and seat mountings and an aerobatic-style harness with a rotary belt latch on the passenger seat harnesses that was cumbersome to operate.
During the hearing, the Board also noted the regulatory no-man's land for private aircraft operated on public-use contracts. By law, the primary responsibility for guaranteeing safe operation of those aircraft is with the contracting agency and not the FAA. USFS pilot inspector Jim Ramage was among those killed in the accident. However, he was not typed in the S-61N and had limited specific knowledge of the aircraft.
During the NTSB's two-year crash investigation, Carson admitted that one of its managers, who it said was acting alone, altered the flight operations manual's emergency five-minute power-available chart. According to the NTSB, this eliminated a safety margin of 1,200 pounds for emergency reserve power that had been provided in the load calculations. Investigators assumed this was done to secure the "performance-based" contract from the USFS. The actions of that unnamed manager, since fired by Carson, are believed to be the primary focus of the ongoing federal criminal probes that began in 2009.
However, in separate interviews with AIN following last month's NTSB hearing, Carson president Frank Carson and William Coultas, the surviving copilot of the crashed S-61N, both strongly disputed that those charts or the helicopter's misstated weight were primary causes of the crash.
Carson continues to question the role played in the accident by a contaminated fuel control unit on the aircraft's Number Two GE CT58-140-1 engine. Shortly after Coultas was hospitalized he said he saw a torque split on the gauges for the number-two engine and engaged the emergency throttle for that engine in the moments before impact. Post-crash investigation found that throttle half-way engaged. Coultas confirmed this statement to AIN on Dec. 13, 2010. He also disputed the NTSB's temperature data as well as Sikorsky's acoustic modeling of the cockpit voice recorder, which concluded that he and pilot-in-command Roark Schwanenberg flew the S-61 to engine topping before the crash.
The NTSB Materials Lab report on the components revealed significant scoring of, and contaminants in, the pressure regulating valve (PRV) of both FCUs. Contaminants in an FCU's PRV can cause it to stick and the engine it serves to lose power. A Transport Canada investigation of a Hayes Helicopter S-61N crash in 2002 faulted a sticking PRV as a contributor to that crash. Further blurring the matter, Carson continues to assert that key components of the suspect FCU went missing during the investigation.
While the NTSB acknowledged and investigated the circumstances surrounding the missing parts, it discounted the role of the FCU in the crash. However, it did find that new 10-micron airframe fuel filters reduce the risk of sticking PRVs and recommended their future use on CT58 engines. Memos between GE, Sikorsky and FCU overhauler Columbia Helicopters related to long-standing problems with sticky FCU PRVs, and subsequent power losses, were released by the NTSB as part of the public docket of the investigation.
In the aftermath of the 2008 crash, Carson stood down and did not resume Part 135 flights. It recently relinquished its certificate after selling the last helicopter enrolled on it. Frank Carson told AIN that the decision to surrender the 135 certificate had been made well before the NTSB hearings and was based on Carson's decision to concentrate on its refurbishment and engineering businesses.
Frank Carson said he completely disagrees with the NTSB's findings and that he and the company are cooperating fully with the ongoing criminal investigation. He plans another reenactment of the crash flight this summer and will invite the NTSB to witness it. Carson said that the Board declined to participate in two previous reenactments in S-61Ns, one performed by Carson and the other by VIH Helicopters. Carson claims the results showed that the crash helicopter should have been able to take off successfully at the altitude, weight and temperature conditions at the time of the crash.
Coultas continues to recover from his injuries. He cannot definitively say if the S-61 could have flown off with reduced power had it been operating at a lighter weight. However, Coultas did say that a successful autorotation, given the helicopter's 15 knots transition forward speed and tree-top altitude, was not possible.
The full NTSB report is expected to be published later this month.