N911VC

History of the Flight

On June 30, 1993, at 1035 hours Pacific daylight time, a Bell 206L-3 helicopter, N911VC, was destroyed during a controlled burn operation, about 3 miles north of Agoura Hills, California. The helicopter was being operated as a visual flight rules (VFR) public use flight when the accident occurred. The helicopter, operated by the Ventura County Sheriff's Department, Ventura, California, was destroyed by a ground fire. The certificated commercial pilot received minor injuries. A non-certificated crew chief was not injured. Visual meteorological conditions prevailed. The flight originated from Camarillo, California, at 0530 hours.

The crew reported that the helicopter was assisting ground fire units in a controlled burn of about 500 acres of grassland in the Santa Monica Mountains National Recreational Area. The aircraft was dispensing small plastic balls onto the grass from an aerial ignition device (AID) that was positioned at the rear door of the helicopter. All of the helicopter's doors were removed for the flight. After completing a dispersal pattern about 100 feet above the ground, the pilot selected a nearby unburned hill for a landing.

Prior to leaving the burn area, the crew chief reported that he turned off the AID unit and cleared the mechanism of any ignition balls by rotating the mechanical operating knob on the right side of the unit. The pilot landed on the hill in about 3 foot high grass for a short break and positioned the engine throttle at flight idle. About 5 minutes later, the crew chief noticed flames on the ground on the right side of the aircraft. He exited the helicopter and attempted to extinguish the flames with a fire extinguisher and a jug of water. The ground fire quickly spread under and around the aircraft, and began curling into the interior. At the start of the fire, the crew chief and pilot both reported that they did not notice any fire in the interior of the helicopter.

The crew chief, while outside the aircraft, was unable to contain the fire and notified the pilot to take off. The pilot reported that he rolled the engine throttle toward the full open position; however, did not notice any immediate increase in engine power. The flames were beginning to burn the pilot, and both crew members made an emergency egress from the fire scene. The helicopter's engine and rotors continued to run.

A ground witness reported observing the helicopter land on the hill. About 5 minutes later, he noticed about an 8 foot diameter burn area under the helicopter with flames about 4 feet high. Other witnesses observed the flight crew evacuate the right side of the aircraft and called for another helicopter to respond to the accident scene.

Another helicopter (aircraft number 7) equipped with an aerial water tank was called to the scene and arrived within about 2 minutes. An aerial drop of water onto the fire scene that now measured about 20 by 20 feet, and the running helicopter, failed to extinguish the fire. The aerial tanker helicopter continued to make 5 to 6 aerial drops on the scene in about 1 minute intervals. The aircraft was subsequently destroyed by the ground fire.

The accident occurred during the hours of daylight at latitude 34 degrees 12.11 minutes north and longitude 118 degrees 44.39 minutes west.

Damage to Aircraft

The helicopter (Ventura County aircraft number 4) was destroyed by the ground fire. The estimated value of the aircraft was 700,000 dollars.

Other Damage

The brush fire at the accident site consumed about 10 acres of grassland before being contained by Ventura County and U.S. National Park Service fire fighters.

Crew Information

The pilot holds a commercial pilot certificate with a rotorcraft helicopter rating and private pilot privileges with airplane single engine land and glider ratings. The most recent second class medical certificate was issued to the pilot on December 23, 1992 and contained the limitation that correcting lenses be worn while exercising the privileges of his airman certificate.

The crew chief does not hold an FAA airman certificate. He has been assigned to the aviation unit for the past 2 and 1/2 years. The Ventura County Aviation Unit does not utilize permanently assigned crew chiefs. Crew chiefs are normally assigned to various units within the Sheriff's Department and report for duty with the aviation unit only part time, usually about 6 days a month.

The pilot and crew chief reported that the accident flight was the first time that either had actually used the AID unit on a fire. The crew chief indicated that he was introduced to the AID in January, 1991, and was given 4 to 6 hours of training in its operation. The crew chief again familiarized himself with the unit in 1992 and also before the accident flight. The pilot was familiar with aerial tactics and procedures utilized in control burn situations and had used other aerial ignition devices (Heli-torch) in the past. Both crew members indicated that they discussed the procedures that would be utilized with the AID unit before the flight.

Aircraft Information

The helicopter had accumulated a total time in service of 2,008.5 flight hours. Examination of the maintenance records revealed that the most recent annual inspection of the airframe and engine was accomplished on April 2, 1993, 38.4 flight hours before the accident. Examination of the maintenance and flight department records revealed no unresolved maintenance discrepancies against the aircraft prior to departure.

The helicopter was last fueled with 45 gallons of Jet-A fuel from a mobile fuel tender that was parked at the staging area. The pilot estimated that the helicopter contained about 58 gallons of fuel at the time of the accident.

The aerial ignition device utilized by the crew was a Premo MK-3, manufactured by Aerostat Inc., Leesburg, Florida. The unit utilizes small plastic balls that contain powered potassium permanganate. The balls produce heat and flame after being pierced by a needle that injects ethylene glycol into the ball. The percent of glycol (mixture can be diluted by water) injected into the ball will produce a varied ignition time. A 100 percent solution of glycol will initiate burning of the ball in about 30 seconds and a 50/50 mixture of glycol and water will produce ignition in about 60 seconds. The unit incorporates a water tank that is available to extinguish any fire occurring in the machine. The crew reported that the unit had about a 75 percent glycol and 25 percent water mix. The balls reportedly cannot ignite unless glycol has been injected, and by themselves (without injection) are not a source of ignition. When subjected to fire, without glycol injection, the plastic outer case of an un-pierced ball melts, and produces a clump of potassium permanganate powder residue.

The balls are fed into the machine from a hopper positioned above four loading chutes. The balls are held in the chutes and prevented from dropping into the machine by a pivoting mechanical lever. If the lever is positioned in the up position, the balls drop into four sliding shuttle blocks. If the lever is down, the balls are held in the chutes and cannot enter the machine; however, as many as eight balls may still be in the machine below the lever once it is placed in the down position.

Once inside the machine, the balls drop into a hole in one of 4 sliding shuttle blocks. The blocks, powered by an electric motor, move a ball forward where it contacts a spring loaded plunger adjacent to the glycol injection needle. As the plunger is compressed, this allows glycol to flow through the needle after it pierces the plastic ball. The block then moves the ball rearward, away from the needle, and the plunger extends to shut off the glycol. The rearward movement of the shuttle allows the ball to be positioned over the vertical discharge chute that hangs over the lower door sill of the helicopter. When installed, the discharge chute hangs down about 2 feet below the bottom of the fuselage, between the fuselage and skid tube, and about 18 inches above the ground. The ball drops down the chute and onto the ground where it ignites. If a ball that has been pierced gets caught in the machine and burns, the fire can be extinguished by utilizing the water spray button, or by pouring water down the loading chute.

Ethylene glycol is supplied to the needle/plunger from an internal tank by a small electric pump. Activation of the pump pressurizes the line from the tank to the plunger. If the pump switch is "OFF", after being previously in the "ON" position, pressure is still present in the glycol line. Activation of the shuttle blocks (either electrically or manually) and piercing of the plastic balls, will still produce a small flow of glycol into the ball due to residual pressure in the glycol line.

The aerial ignition device normally receives continuous electrical power from an auxiliary power receptacle installed in cockpit area of the helicopter. The power to the unit would therefore be controlled by the rear seat crew member utilizing unit mounted switches. The unit in the accident aircraft, received its electrical power from an electrical circuit receptacle that was installed for use with U.S. Forest Service equipment (Heli-torch) that normally is suspended from the helicopter's cargo hook. The electrical circuit incorporates a button mounted on the pilot's collective control. The pilot must keep the button depressed to energize the circuit, thereby providing power to the unit. If he lets the button up, electrical power is removed.

The pilot reported that when the collective electrical switch was initially installed by maintenance personnel, a small metal guard was fabricated to provide protection from inadvertent activation of the switch. He indicated that some time prior to the accident flight, the guard was misplaced or broke and had not been...