N911VC – Bell Textron 206L-3 – 1993-06-30 NTSB Accident Report

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 replaced. The pilot indicated that he was more comfortable with controlling the AID unit from the pilot's position as he was not comfortable that the crew chief had sufficient knowledge of aerial fire control procedures.

The pilot reported that the crew chief would notify him that the AID unit was ready to dispense the balls and he would control the dispensing of the balls by depressing the electrical switch on the collective. After finishing a dispensing pattern, the pilot would announce to the crew chief that he was stopping dispensing, and the crew chief would turn off the AID unit switches and clear the machine of any plastic balls.

Switches on the right side of the unit allow the operator to select glycol ON/OFF, power ON/OFF, and a speed selector switch that has a FAST/SLOW position. A button on the right side energizes the emergency water injection. The unit also incorporates a knob on the right side of the housing that allows the operator to manually move the shuttle blocks to clear the blocks of any balls. Visual inspection of the contents of the shuttle blocks and status of the discharge chute is prevented by the position of the loading chute housing.

The crew chief reported that after completing the last aerial dispensing pattern and before landing at the accident site, he turned off the AID unit and cleared the shuttle blocks of any balls by manually rotating the knob on the side of the machine. After landing, while the helicopter was sitting at flight idle, he prepared the AID unit for the next pattern. He reloaded the hopper with plastic balls, turn the power and glycol switches to the ON position and opened the manual gate that allows the balls to fall into the shuttle blocks. He did not communicate the status of the AID unit to the pilot.

Meteorological Information

The closest official weather observation station is Camarillo, California, which is located about 20 nautical miles west of the accident site. At 1046 hours, a surface observation was reporting in part:

Sky condition and ceiling, clear; visibility, 10 miles; temperature, 74 degrees F; dew point, 62 degrees F; wind, 200 degrees at 7 knots; altimeter, 29.79 inHg.

The weather conditions at the accident scene were reported by the crew to be:

Sky condition and ceiling, clear; visibility, 20 miles; temperature, 85 degrees F; wind, 240 degrees at about 5 knots.

Wreckage and Impact Information

Safety Board investigators examined the helicopter wreckage at the accident site on June 30, 1993. The wreckage examination revealed that the helicopter had landed on a grass covered hill on about a 180 degree heading (all heading/bearings noted in this report are oriented toward magnetic north). The grass was an average height of about 3 feet and was consumed in the immediate area around the helicopter for about a 100 foot radius.

All of the helicopter's components were found at the main wreckage area. The helicopter was consumed by fire from the nose to the tail boom forward attach point. During the structural collapse of the fuselage, the upper deck components of the aircraft, including the engine, main rotor transmission, and hydraulic servos were found positioned lying to left side of the fuselage.

The main rotor blades were attached to the rotor hub and rotor mast/transmission were lying on its left side. The blades were oriented parallel to the longitudinal axis of the helicopter. A circular ground scar was found on the left side of the wreckage consistent with the main rotor blade tip path. The engine was attached to the engine mounts and was also lying on its left side.

The nose section of the helicopter was lying to its left side with the cockpit area consumed by fire. Examination of the pilot's collective control revealed that the forward end of the control that normally contains engine start buttons, RPM control, landing light switches, and the electrical power switch utilized to energize the aerial ignition device, was completely consumed by fire.

The lateral landing gear cross tubes were melted at the fuselage. The left landing gear skid tub was fractured about 6 inches aft of the forward cross tube attach point. The interior cockpit and cabin area was consumed by fire. The rear fuel tank structure under the rear seat was visible along with the forward left side fuel cell that is positioned under the left side rear facing seat. The forward right side fuel cell under the right aft facing seat, along with the adjacent lower aircraft structure, was consumed. The aerial ignition device was located lying on its left side, adjacent to the right cabin door, just forward of the right rear flight step.

The tail boom was intact from the forward fuselage attach point aft and was lying on the ground. Fire damage and blistering of the paint was noted on the upper and lower surface of the tail boom from the forward attach point to the horizontal stabilizers. Heat damage with peeling and blistering of paint was present on the lower surface of the tail boom from the horizontal stabilizers to the aft end of the boom. The left horizontal stabilizer exhibited heat damage and peeling of the outer, bottom surface. A semi-circular impression oriented parallel to the longitudinal axis of the aircraft was noted on the ground under the tail rotor blades tip path.

Examination of the ground under the belly of the helicopter revealed that the grasses were completely burned with no visible unburned areas. Examination of the ground under the right landing gear skid tube revealed areas of unburned grass under the skid.

Examination of the aerial ignition device revealed that the loading hopper was consumed by fire. Residue from the supply of ignition balls was present next to the machine. The machine exhibited fire damage and melting on the rear (inside end) and left side of the unit. The loading chutes, shuttle blocks, and discharge chute were smoke damaged but not melted. The locking lever was in the up, non-locking position. The glycol switch was in the ON position; the power switch in the ON position; and the speed select switch in the SLOW position.

Inspection of the shuttle blocks after removal of the loading chute housing revealed that powder residue was visible in the number 2 and 4 (from left to right) blocks. The number 3 block was empty. The number 1 block, positioned over the discharge chute, had residue adhering to the left side of the block. Residue was found at the lower end of the discharge chute.

Fire Aspects

A Ventura County Fire Protection District arson investigator accompanied Safety Board investigators and examined the accident scene. He reported that the burn patterns in the grass indicated that the fire originated at the point were the helicopter had landed. The grass fire spread in a northeasterly direction. He also indicated that the fire was ignited by a ball from the dispensing unit in the helicopter.

Survival Aspects

Both crew members were wearing non-flammable flight suits, helmets, boots and nomex gloves. Their protection from the flames and egress from the fire was added by the use of this equipment. The pilot did receive facial burns when flames curled into the cockpit area.

Tests and Research

Portions of recovered powder residue were examined by the Ventura County Sheriff's Department Criminalistics Laboratory, for the presence of potassium permanganate and ethylene glycol. The laboratory reported that the recovered material was potassium permanganate. Due to the numerous variables as a result of the fire, the presence of ethylene glycol could not be determined.

Additional Information

Safety Board investigators reviewed the training syllabus and standard operating procedures utilized by the U.S. Department of the Interior for the employment of the Premo Mark III Aerial Ignition Device on departmental or contracted aircraft. The syllabus involves 6 to 8 hours of training on the function of the unit, normal and emergency operation, maintenance of the unit, an actual in-flight operation of the unit, and a written test. The training syllabus also includes verbal commands that are to be used between the pilot/burnboss and the operator. In section III, Installing Machine in Aircraft, of the training syllabus, step 4 states:

"Connect power supply cord to the machine. Warn trainees that under no circumstances will the power supply cord be connected to the helitorch power supply source or to any other power source that can be activated or deactivated by anyone other than the operator."

Safety Board investigators also reviewed the Ventura County Sheriff's Aviation Unit's standard operating procedures (SOP), and the crew chief training syllabus. Crew chief training does not include any structured training on the AID unit. The crew chief training syllabus does contain a rating system on each of the training areas; however, does not have any provision for entry of a completion date or recurrent training. The syllabus does not contain any training in crew coordination or crew communication.

Safety Board investigators did not locate any pilot training, or recurrent training records. The Aviation Unit's SOP is not a formally adopted document by the Sheriff's Department administration. The unit has not designated a safety officer, training officer, chief/senior pilot, or chief/senior mechanic.

Wreckage Release

The Safety Board released the wreckage, located at the Ventura County Sheriff's Department, to departmental personnel on August 31, 1993. No parts or components were retained by the NTSB.