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N34698 accident description

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Tail numberN34698
Accident dateAugust 17, 2004
Aircraft typeBell 206B
LocationMead, WA
Near 47.788889 N, -117.349444 W
Additional details: None

NTSB description

On August 17, 2004, at 0940 Pacific daylight time, a Bell 206B helicopter, N34698, was destroyed when it impacted terrain following a loss of control while hovering out of ground effect with an external load near Mead, Washington. The airline transport pilot, the sole occupant, was fatally injured. The helicopter was registered to and operated by the United States Department of Energy (DOE). The purpose of the public use flight conducted under Title 14 CFR Part 133 was to assist in stringing power lines for the Bonneville Power Administration (BPA). Visual meteorological conditions prevailed, and a company flight plan was filed. The flight departed from Spokane International Airport in Spokane, Washington at 0655.

INFORMATION FROM FAA

According to information gathered by FAA inspectors who responded to the accident site, the helicopter was pulling sock line (rope) that was to be used to install a static wire at the top of 220-foot-tall towers supporting a 500-kV power line. (The stringing of sock line is a Class C external load operation, meaning an operation in which the external load is jettisonable and remains in contact with land or water during the rotorcraft operation.) The sock line was attached to the helicopter's remote cargo hook and played out of a truck mounted reel machine. The reel machine operator provided a written statement to the FAA inspectors stating that "suddenly the rope wrapped over another rope or pulled down in the drum, causing the rope to reverse on the drum." The reel machine operator immediately moved the machine's shift lever from "OUT" to "NEUTRAL," but by the time he had accomplished this, the rope between the reel and the helicopter went taut. Numerous witnesses, who were all members of the line crew installing the wires, reported that when the rope went taut, the helicopter pitched up and rolled right. The helicopter descended, impacted the ground and came to rest on its right side. A small fire erupted near the engine compartment, which the line crew extinguished with their fire extinguishers. They then used a winch to raise the helicopter upright to gain access to the cabin and render first aid.

Examination of photos and a diagram provided by the FAA inspectors revealed that the 500-kV power line was oriented east-west, and the helicopter was pulling the sock line from the east towards the west. The helicopter came to rest about 700 feet west of the reel machine, near the base of a 13.8-kV power line that ran perpendicular to and beneath the 500-kV power line. One of the wooden towers supporting the 13.8-kV power line was damaged. Pieces of the wooden cross arms were broken off the tower, and there was evidence of a main rotor blade strike to one of the tower's poles about 18 feet agl. The right side of the helicopter's fuselage was crushed inward. The main rotor system, the vertical fin, the forward cross tube, the left skid, and one tail rotor blade were separated from the helicopter. All of the damage to the helicopter appeared to be impact related. The helicopter's 25-foot long line was severed about 5 feet below the helicopter's belly hook. The shackle on the upper end of the long line was still attached to the belly hook; however, the long line's electrical plug was disconnected from the mating plug on the belly of the helicopter. The other section of the long line ending with the remote hook to which the sock line was still attached was found hanging from a chain link fence about 70 feet east of the helicopter.

INFORMATION FROM DOE

Personnel with the DOE conducted witness interviews, examined the accident site, and prepared a report of their observations. According to the DOE report, the helicopter was being used to string sock line to enable the subsequent stringing of new conductors and static wire on the 500-kV power line. The helicopter was needed in order to pass the sock lines over nine energized power lines that crossed under the 500-kV line. (These nine energized power lines were in addition to the 13.8-kV line described above which was de-energized.) The sock line would later be used by the line crew to pull the heavier conductors and static wires.

The first part of the job involved pulling sock line from a triple drum puller/tensioner (reel machine) for the three conductor wires. The second part of the job involved pulling sock line from a single drum puller/tensioner for the two static wires. Interviews conducted by DOE personnel revealed that on August 12, 2004, the pilot met with the line crew to discuss the sock line pull. The triple drum operator and the pilot discussed the operation of the puller/tensioners and whether to free-wheel or power payout the sock line. The pilot indicated that he had been told by the BPA Chief Helicopter Pilot that as long as the line would come off the reel at a fast walking pace, it would be adequate for the operation. The triple drum operator paid out the sock line under power from the triple drum puller as the pilot walked with it at a fast pace. As a result of this test, the pilot was satisfied with the speed of power payout. This test was not repeated with the single drum puller.

The Chief Pilot later reported to the DOE investigators that he intended the reel to be freewheeling and assumed the pilot understood this. The DOE report noted that in the freewheel mode, when a snag occurs, at worst, the reel stops. In the power payout mode, when a snag occurs, the line can double back on the reel and begin to pull back in.

On August 16, 2004, the pilot and the line crew attended an in-depth briefing of the work at a "tailboard" meeting. The tailboard meeting included a helicopter safety briefing given by the job foreman that covered ground crew safety. According to the DOE report, the helicopter briefing did not include a general discussion of "such topics as how to respond to emergency situations like sock line hang-ups, other hazards specific to Class C loads, or other detailed helicopter operational procedures." However, conversations between the pilot and individual crewmen took place during which some of these issues were discussed.

Witnesses interviewed by the DOE investigators reported that the helicopter landed at the work site about 0700 on the day of the accident. The pilot shut down the helicopter and attached a 25-foot long line with a 31-pound ballast and remote cargo hook to the helicopter's belly hook. The pilot and one of the linemen (a heavy mobile equipment mechanic) physically checked the range of motion in all directions of the belly hook with the long line attached to ensure that it would not interfere with the remote hook's electrical connection at the belly of the helicopter. The pilot and a lineman then tested the remote hook to ensure that it operated electrically and mechanically.

Later examination of the helicopter by the DOE investigators revealed that the pilot did not wrap electrical tape around the remote cargo hook's electrical connection at the belly of the helicopter. The investigators found that there was no written requirement in the BPA Aircraft Services External Load Manual to perform this task. They noted that experienced pilots conducting external load operations commonly take this precaution to prevent inadvertent disconnection of the remote hook's electrical connection, which disables the pilot's remote cargo hook electrical jettison switch. (The remote cargo hook electrical jettison switch is one of three methods the pilot can use to jettison an external load. The other two methods are the belly hook electrical jettison switch and the belly hook manual release handle.)

Prior to commencing the work, the pilot discussed the use of the triple drum puller with an equipment operator. Approximately 0850, the helicopter began the conductor sock line pulls from the triple drum puller with the puller in the power payout mode. These three pulls were accomplished without incident.

During the morning, in preparation for the static sock line pulls, a lineman and the equipment operator of the single drum puller were in the process of placing the machine in free-wheel mode when they were stopped by another lineman who informed them that the pilot wanted the puller in the power payout mode. The ground crew then walked the sock line off as the operator power paid it out to establish the adequacy of the payout speed. While walking out the sock line, a ground crew member experienced a tug on the line that spun him around and pulled him back towards the machine. The equipment operator told the ground crew member that he had a snag in the line, which resulted in the line doubling back and pulling onto the reel. According to the DOE report, "such a snag is not uncommon in the use of puller/tensioner equipment and when not using a helicopter is not considered a safety hazard."

Approximately 0935, the pilot maneuvered the helicopter to a position to initiate the static sock line pulls. The pilot did not land the helicopter and discuss this part of the work with the ground crew before proceeding. After the sock line was hooked to the remote hook, the helicopter began to move backward. (The BPA Aircraft Service's technique for pulling sock line with a Bell 206B is to position the helicopter with the nose 15 degrees left of centerline and then fly rearwards.) Evidence collected by the DOE investigators indicates that the helicopter had traveled approximately 700 feet from the single drum puller when a snag on the reel occurred. Due to the snag, the line started to pull in, even though the reel rotation was in the proper (out) direction. The puller operator sensed the machine lugging down, noticed the snag and attempted to shift the power lever to neutral. Measurements taken by the DOE investigators indicated that for approximately 6 seconds, the machine pulled about 36 feet of sock line back onto the reel. The operator overshot the neutral detent and shifted into reverse. The sock line again snagged and doubled back on itself. Before the operator shifted the machine to neutral, an additional 9 feet 7 inches of sock line were pulled back onto the reel.

The DOE investigators determined that the combination of the snagged sock line and the helicopter's motion away from the puller removed all slack from the sock line and the helicopter's long line, resulting in "a sudden jolt that rocked the aircraft back on its tail." They further determined that "this jolt more than likely unplugged the power source to the remote-hook release, preventing the pilot from jettisoning the sock line remotely." Witnesses reported that the helicopter nosed down and turned about the mast centerline pulling the long line taut against the belly of the helicopter, trailing aft. The DOE investigators found physical evidence indicating the helicopter's left skid then struck the upper wooden cross arm of the 13.8-kV power line, and the long line contacted one of the two static wires on this power line. The helicopter pivoted around the static wire and pitched nose down, the long line was severed by the static wire, and the helicopter fell to the ground.

The DOE investigators examined the belly hook in an attempt to determine why the pilot did not jettison the external load using either the belly hook's electrical jettison switch or its manual release handle. The cargo suspension system installed on the helicopter was a Bell Kit 206-706-35, which included a 1,500-pound capacity cargo hook manufactured by Breeze Eastern Corporation, a suspension system frame, a mechanical release cable, an electrical connection, and associated hardware. On the forward-facing side of the cargo hook was a plastic housing where a cannon plug was mounted for connection of the wiring to the pilot's belly hook electrical jettison switch. On the aft-facing side of the cargo hook was another plastic housing where a manual release knob attached to a shaft that, when turned by hand, opened the hook. The DOE investigators found that when the belly hook was pulled full forward, the plastic housing where the cannon plug mounted contacted the cargo suspension frame. They also found that when the belly hook was pulled full aft, the manual release knob contacted the frame.

Examination of the belly hook by the DOE investigators revealed that the plastic housing around the cannon plug was damaged, the cannon plug was dislodged from the housing, and two wires were pulled out of the cannon plug. Once this damage occurred, it rendered the pilot's belly cargo hook electrical jettison switch inoperative. Additionally, it was found that the manual release knob had been knocked off its shaft. Damage to a rubber bumper on the cargo suspension frame indicated the exposed shaft had been pushed into the bumper. The investigators held the cargo hook in the full aft position such that the shaft was embedded in the rubber bumper and activated the electrical solenoid that opens the hook. With the shaft embedded in the bumper, the solenoid would not open the hook. Under these conditions, the manual release handle was still functional and when activated, would open the hook. The investigators concluded that either the damage to the cannon plug or the shaft being pushed into the bumper prevented the pilot from jettisoning the load from the belly hook electrically. The investigators could not determine why the pilot did not release the load manually; however, the DOE report stated that due to the rapidity of the event, "it is highly unlikely that the pilot had enough time to use the manual load release lever."

The DOE investigators conducted surveys and interviews with other North American operators utilizing helicopters equipped with belly-mounted cargo hooks to determine what rigging they use when conducting Class C loads. The responses were that they have learned to use heavy ballast when pulling sock line with a belly mounted cargo hook, regardless of the make or model of helicopter. The pilot maneuvers the helicopter to control the ballast, and the ballast weight's momentum pulls the sock line. The shorter the long line, the more ballast they use. As an example, one operator stated he used 600 pounds of ballast when using a 20 foot long line, but on a 100 foot long line, he used 200 pounds of ballast. These combinations of ballast weight and long line length are used to provide a warning to the pilot of an impending shock load due to a snag and allow for a timely response. If the long line and ballast departs more than 15 degrees from vertical, it is released.

According to the DOE report, the pilot had accumulated 21,803 hours of rotorcraft flight experience including 16,000 hours in Bell 206 series aircraft over a 36-year career. In the last 30 and 90 days, the pilot had flown 34 and 116 hours, respectively, all in the Bell 206. According to his company (BPA) flight records, the pilot had accumulated 4,000 hours conducting external load operations including 3,000 hours conducting long-line operations. The records indicated that on June 28, 1996, the BPA Chief Helicopter Pilot observed the pilot conducting a Class C operation with 50-, 100-, and 150-foot long lines. The company records indicated the pilot's most recent Class C load operation occurred on May 6, 1999. His most recent external load experience was in Class B operations and occurred in April 2003.

MEDICAL AND PATHOLOGICAL INFORMATION

An autopsy of the pilot was performed at the Spokane County Medical Examiner's Office in Spokane, Washington. Toxicological tests performed by the FAA's Toxicology and Accident Research Laboratory were negative for carbon monoxide, cyanide, and ethanol. Diliazem, a prescription medication used to treat certain cardiovascular conditions, including hypertension, was detected in the pilot's blood. A review of the pilot's FAA medical revealed that the pilot had reported the use of this medication on his most recent application for a medical certificate, dated September 23, 2003. The records further revealed that the pilot had a history of hypertension controlled by medication. In 1998, 2001, and 2002, the FAA had reviewed medical records pertaining to the pilot's hypertension and determine

(c) 2009-2011 Lee C. Baker. For informational purposes only.