Helicopters are used by logging companies in the Alaska panhandle to harvest timber in areas that otherwise are inaccessible and/or unfeasible for conventional logging (because of rugged terrain, steep mountain slopes, environmental restrictions, or high cost). The National Transportation Safety Board (NTSB) investigated six helicopter crashes related to transport of logs by cable (i.e., long-line logging*) that occurred in southeastern Alaska during January 1992-June 1993 and resulted in nine fatalities and 10 nonfatal injuries. This report presents case investigations of these incidents. Incident Reports

Incident 1. On February 23, 1992, a helicopter crashed while transporting nine loggers. The copilot and five loggers died; five others were seriously injured. The NTSB investigation revealed that a long-line attached to the underside of the helicopter became tangled in the tail rotor during a landing approach, causing an in-flight separation of the tail section (1). Passenger flights with long-line and external attachments are illegal (2) and violate industry safety standards.

Incident 2. On March 6, 1992, a helicopter crashed while preparing to pick up a load of logs with a long-line. The pilot and copilot were seriously injured. According to the pilot and copilot, the engine failed, and the pilot immediately released the external log load and attempted autorotation **.

Incident 3. On November 10, 1992, a helicopter crashed while attempting to land at a logging site, sustaining substantial damage. The solo pilot was not injured. NTSB investigation revealed that the helicopter's long-line had snagged on a tree stump during the landing and that the company had no documented training program (1).

Incident 4. On February 19, 1993, a helicopter crashed from a 200-foot hover after transporting two logs to a log-drop area. The pilot and copilot were killed. NTSB investigation revealed in-flight metal fatigue of a flight-control piston rod.

Incident 5. On May 2, 1993, a helicopter crashed during an attempted emergency landing after using a long-line to lift a log 1200 feet above ground level followed by rapid descent to a 75-foot hover. The pilot died, and a logger on the ground was injured. NTSB investigation revealed an in-flight separation of the tail rotor and tail rotor gear box from the helicopter. The company had been using a flight procedure that would have heavily loaded the helicopter drive train (1).

Incident 6. On May 8, 1993, a helicopter crashed after attempting to lift a log from a logging site with a long-line. The pilot and copilot sustained minor injuries, but the aircraft was substantially damaged. NTSB investigation found that the engine failed because machine nuts had come loose from the engine or its housing and became caught in the engine. The helicopter crashed when the pilot attempted autorotation. Investigation Findings

Statewide occupational injury surveillance in Alaska through a federal-state collaboration was established in mid-1991, with 1992 being the first full year of comprehensive population-based occupational fatality surveillance for Alaska. During the time these incidents occurred, an estimated 25 helicopters in Alaska were capable of conducting long-line logging operations; approximately 20 were single-engine models from one manufacturer (Federal Aviation Administration {FAA}, unpublished data, 1993). Approximately 50 helicopter pilots were employed in long-line logging operations in southeastern Alaska (FAA and Alaska Department of Labor, unpublished data, 1993). Using these denominators, the events in this report are equivalent to an annual crash rate of 16% (six crashes per 25 helicopters per 18 months), 0.24 deaths per long-line helicopter in service per year (nine deaths per 25 helicopters per 18 months), and an annual fatality rate for long-line logging helicopter pilots of approximately 5000 deaths per 100,000 pilots (four pilot deaths per 50 pilots per 18 months). *** In comparison, during 1980-1989, the U.S. fatality rate for all industries was 7.0 per 100,000 workers per year; Alaska had the highest overall occupational fatality rate of any state (34.8 per 100,000 per year) for the same period (4).

According to NTSB investigations to determine probable cause, all six crashes involved "...improper operational and/or maintenance practices" that reflected a lack of inspections of long-line helicopter logging operations (1). In incidents 4, 5, and 6, investigative evidence also indicated that log loads routinely exceeded weight and balance limits for the aircraft. Following increased inspections, no additional logging-related helicopter crashes were reported through June 30, 1994.

Reported by: G Bledsoe, Occupational Injury Prevention Program, Section of Epidemiology, Div of Public Health, JP Middaugh, State Epidemiologist, Alaska Dept of Health and Social Svcs; D Study, Labor Standards and Safety Div, Occupational Safety and Health, Alaska Dept of Labor. National Transportation Safety Board, Anchorage, Alaska. Alaska Activity, Div of Safety Research, National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: The incidents in this report demonstrate that long-line helicopter logging is a technology application with an unusually high risk for occupational fatalities. General aviation regulations restrict the number of hours pilots can fly during given time periods; however, long-line helicopter logging involves carrying loads outside the rotorcraft, and there are no legal limitations on crew flight hours. Although flight-crew work schedules and daily flight hours vary greatly by logging company, flight-crew duty periods can exceed 10 hours per day for 10 consecutive days.

Helicopter logging operations often place heavy demands on helicopter machinery and associated equipment. The highly repetitive lift/transport/drop cycles are frequently conducted at or beyond maximum aircraft capacity in remote areas, where rugged terrain, extremely steep mountain slopes (as great as 70 degrees), and adverse weather conditions prevail. Complex operations under such circumstances may increase the likelihood of both human error and machine failure (5). In addition, conditions are unfavorable for successful autorotation during most helicopter long-line logging operations.

Regardless of where helicopter logging operations are conducted, the jurisdictional responsibility for inspection rests with the FAA office nearest the main or registered corporate office for the helicopter company (in all of the cases in this report, these offices were in the contiguous United States). This necessitates travel of great distances to conduct helicopter logging inspections, and remote operations may escape or evade inspection for long periods. The NTSB has recommended that operational and maintenance oversight responsibilities for remote sites be assigned to the nearest FAA office (1).

In response to these incidents, the Alaska Federal-State Interagency Collaborative Working Group on the Prevention of Occupational Traumatic Injuries **** met in a special session on July 8, 1993, to discuss approaches for reducing the number of such crashes and ameliorating the outcome of crash injuries. Based on these and other findings, the working group made the following recommendations (6):

All helicopter logging pilots and ground crews should receive specific training in long-line operations.

Companies should follow all manufacturers' recommendations for more frequent helicopter maintenance (because of intensity of use) and for limits on maximum allowable loads.

Companies should establish and observe appropriate limits on helicopter-crew flight time and duty periods.

Companies should consider using multi-engine rotorcraft. Specific industrywide operating standards and procedures should be developed.

Companies should provide training in on-site emergency medical care for helicopter logging crews at all work locations.

State, regional, and local agencies involved in emergency medical services education should make low-cost emergency medical training available to persons likely to work in a helicopter logging environment.

All flights over water should include appropriate survival equipment for all crew and passengers, who should wear personal flotation devices at all times during flights over water.

References

1. National Transportation Safety Board. NTSB safety recommendation A-93-78 through -80. Washington, DC: National Transportation Safety Board, June 17, 1993.

2. Office of the Federal Register. Code of Federal Regulations, Vol 14, part 133. Washington, DC: US Department of Transportation, Federal Aviation Administration, January, 1992.

3. Roland HE Jr, Detwiler JF. Fundamentals of fixed and rotary wing aerodynamics. Los Angeles: University of Southern California, November 1967.

4. Jenkins EL, Kisner SM, Fosbroke DE, et al. Fatal injuries to workers in the United States, 1980-1989: a decade of surveillance. Atlanta: US Department of Health and Human Services, Public Health Service, CDC, NIOSH, 1993.

5. Aircraft accident investigation manual. Los Angeles: University of Southern California, Institute of Safety and Systems Management, December 1992.

6. Helicopter logging: Alaska's most dangerous occupation? State of Alaska Epidemiology Bulletin, August 16, 1993; bulletin no. 32.

* A typical long-line logging helicopter carries an approximately 200-foot load cable (i.e., long-line), which is attached by a hook to the underside of the helicopter. A second hook is fixed to the free end of the cable, where a choker cable (an apparatus designed to cinch or choke around suspended logs) is connected to one to four logs per load. 

** Autorotation allows a helicopter to make an unpowered descent by maximizing on the windmilling effect and orientation of the main rotor forward airspeed and altitude can be converted to rotor energy to reduce the rate of descent. Successful autorotation depends on helicopter airspeed and altitude when the maneuver is attempted (3). Most helicopters conduct long-line logging operations with minimal or no forward airspeed at less than 400 feet above ground level, while optimal conditions for autorotation require an altitude of at least 500 feet above ground level and airspeed of more than 60 knots per hour. 

*** These rates refer to the period of intense collaborative investigation and may not represent incidence over a longer period of time; however, they accurately reflect the high risk of helicopter long-line logging during that interval. 

**** Representatives from the Alaska Department of Health and Social Services, Alaska Department of Labor, FAA, CDC's National Institute for Occupational Safety and Health, NTSB, Occupational Safety and Health Administration, U.S. Coast Guard, and the U.S. Forest Service.

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