NTSB Identification: ANC08FA053
Nonscheduled 14 CFR Part 135: Air Taxi & Commuter
Accident occurred Tuesday, April 15, 2008 in Chickaloon, AK
Probable Cause Approval Date: 03/03/2010
Aircraft: EUROCOPTER AS 350 B2, registration: N213EH
Injuries: 4 Fatal,1 Serious.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The commercial pilot was on a Part 135 passenger flight transporting telecommunication technicians to remote sites. A technician was left at one site, and when the helicopter did not return, he contacted his employer. His employer contacted the helicopter operator. Unable to make contact with the helicopter, the operator contacted the FAA, and reported the helicopter overdue. A search for the helicopter was initiated based on a position report from the helicopter's onboard commercial satellite tracking system. A snowstorm in the search area precluded the use of aircraft in the search, and ground searchers were unsuccessful.
A State Trooper helicopter found the crash site the next morning when the weather improved. The pilot and three passengers were found dead; the fourth passenger, the minor stepson of one of the technicians, had head injuries and hypothermia. According to the operator and survivor, after transporting the first technician, the helicopter landed at a rest area near the highway and picked up another technician and his stepson prior to going to the next site. The stepson was in the left front seat, and the three technicians were in the rear seats. The destination site was about 2.5 miles from the rest area across a ravine. A motorist on the highway saw the helicopter depart from the rest area, and then make a steep descent into a ravine. He said he thought the descent was unusual, but he did not see any impact, and thought the helicopter was working in the ravine. He said the visibility was about 2 miles, and it was snowing lightly.
The helicopter impacted terrain approximately in a level attitude in a near vertical descent, about three-quarters of a mile from the rest area. The terrain at the accident site was rough and uneven, covered with trees, high brush, and snow. The accident flight lasted less than 2 minutes. The surviving front seat passenger recalled the liftoff and departure, then said he felt like he was falling, and that the pilot told everyone to "hold on we're going to crash."
An examination of the helicopter's engine showed free turbine blade shedding consistent with an engine overspeed. The floor mounted fuel flow lever was found captured by fuselage crush in the forward emergency position, and the emergency fuel shutoff lever was captured in the aft shutoff position. During impact, the removable acrylic left chin-bubble popped out, and was found about 3 feet in front of the helicopter's nose. A backpack belonging to the surviving passenger was found between the chin bubble and the nose of the helicopter. All other baggage/cargo was found stowed aft and secured.
The rotor system and drive train had damage consistent with impact. No evidence of any preimpact mechanical failures were discovered other than the turbine blade liberations.
According to the manufacturer, inadvertent movement of the floor-mounted fuel flow lever into the forward emergency position can cause the engine to overspeed within seconds. The fuel flow lever is on the helicopter’s cabin floor, situated near the front seat passenger’s right foot, and is easily moved with minimal pressure. In 1994 a Canadian-registered Eurocopter AS-350-B helicopter crashed after a passenger inadvertently moved the floor mounted fuel flow control lever to the closed position while trying to adjust a knapsack. In 1998 an AS-350-B2 crashed in France when a passenger seated on the floor inadvertently moved the fuel flow control lever to the closed position. Two large US helicopter operators also reported information about passengers accidentally interfering with the floor mounted controls.
As a result of the 1994 crash in Canada, the Canadian Transportation Safety Board (TSB) forwarded an Aviation Safety Information letter to Transport Canada (TC) regarding the possibility of inadvertent manipulation of the fuel flow lever on the AS-350-B helicopter. According to the TSB report, Transport Canada and the industry were investigating the feasibility of installing a control quadrant guard to reduce the likelihood of inadvertent fuel control lever movement. The manufacturer stated that they studied, and proposed, a guard to be installed in a helicopter configuration involving an Emergency Medical Service (EMS) litter installation, but said that due to lack of interest by the operators, the guard was withdrawn as an option in 2007.
In this accident, due to the close proximity of the passenger’s right foot to the unprotected fuel control lever, as well as finding his loose backpack forward of the main wreckage, it is likely that either the passenger’s right foot, or his placement of the backpack, inadvertently moved the fuel control lever into the emergency range, resulting in an engine overspeed and loss of engine power. Given the rough and uneven terrain and the helicopter's low altitude, a successful autorotation landing was improbable. Also the operator's failure to closely monitor the flight's progress, and to make timely inquiries into its welfare, delayed the search and rescue of the survivor or potential survivors, and may have added to the severity of their injuries.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The loss of engine power due to an overspeed of the helicopter’s turbine engine, precipitated by the inadvertent movement of the fuel flow control lever by the passenger. Also causal was the manufacturer's design and placement of the fuel control lever which made it susceptible to accidental contact and movement by passengers. Contributing to the accident was the pilot’s failure to properly secure/stow the passenger’s backpack. Likely contributing to the severity of the occupant's injuries was the helicopter operator’s failure to properly monitor their satellite flight following system and to immediately institute a search once the system reported the helicopter was overdue. Full narrative available
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