N873HL

On September 10, 2023, about 1345 Pacific daylight time, a Bell 212 helicopter, N873HL, was destroyed when it was involved in an accident near Balch Camp, California. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 133 firefighting flight.

The flight was operated by Rogers Helicopters Inc. under contract with the United States Forest Service.

The helicopter was equipped with a Simplex 304 Fire Attack System, composed of a 375-gallon belly-mounted tank, a hover refill pump, and cockpit controls for dispensing the tank’s contents. According to the pilot, he successfully completed eight water drops at altitudes between 6,000 ft and 7,000 ft msl and then returned to his departure airport in Sanger, California, to refuel. The pilot noted that during two separate water pickups that day the pump continued to run after he filled his tank and withdrew the snorkel from the water; however, the pump ceased running after he jostled the switch. At 1315, he departed towards Pine Flat Reservoir to pick up his first load of water at a site about 2,000 ft msl. After he reached the reservoir, the pilot hovered over the water, deployed the snorkel and activated the pump as prescribed by the operating procedure, but immediately noticed that water was spilling from the tank. The pilot disengaged the pump and activated the water tank doors, but did not observe any movement. After he climbed to about 20 ft above the water, he observed the doors move after he cycled the tank power switch on the center console. Subsequently, he reengaged the pump and performed a successful test opening of the tank doors. He ran the pump until he loaded the desired amount of water and then proceeded to the fire area.

The fire was located between 7,000 ft and 8,000 ft msl, surrounded by 100-ft-tall pine trees. During a subsequent orbit of the area the pilot decided to approach the fire from higher terrain. As he approached the fire area he noticed that the helicopter required more power than expected. Although he was not initially concerned, he decided to approach the fire from a direction that would ensure a downhill escape. The pilot then slowed the helicopter; however, he felt that the helicopter still required more power than he expected and decided to jettison the water load. The pilot depressed the drop switch twice, but the water tank doors did not open. The pilot then elected to fly towards a meadow, but when he increased collective control and began the turn the low rotor rpm horn activated and the main rotor contacted a tree. He immediately applied aft cyclic control as the helicopter rapidly descended before it impacted the ground and a post-crash fire ensued.

The helicopter was destroyed by post-crash fire, which consumed the majority of its airframe and components. The main drive shaft to the input quill (between the combining gearbox and the main transmission) were intact but exhibited thermal damage. Circumferential scoring was observed through the input drive shaft tube adjacent to both splined ends. The main rotor blades did not display any evidence of a preimpact failure.

The tail rotor drive shaft was mostly consumed by post-crash fire. A portion of the tail rotor drive shaft remained attached to the intermediate gearbox. Continuity of the drive was confirmed through the intermediate gearbox and rotation of the tail rotor resulted in a corresponding rotation of the tail rotor gearbox input pinion.

Continuity of the flight control system could not be established due to significant fragmentation and post-crash fire.

Both engines had separated from the airframe and were subsequently examined at the engine manufacturer’s facility with oversight from the National Transportation Safety Board (NTSB). Neither engine exhibited any evidence of a preimpact mechanical anomaly that would have precluded their normal operation.

The pilot completed a load calculation before the accident flight, which had the date and time of September 9, 2023, 0930 for the mission “initial attack fire.” The load calculation performance reference was for Bell 212HP helicopters equipped with the Boundary Layer Research FastFin (BLR FF), which was installed on the accident helicopter in 2018. The BLR FF incorporates physical changes to the vertical fin and adds tail boom strakes to improve aerodynamic efficiency during hover. A rotorcraft flight manual supplement (RFMS) for helicopters equipped with the BLR FF contains revised performance charts. The total calculated helicopter weight with equipment, personnel and fuel was 8,642 lbs and the jettisonable allowable payload for hovering out of ground effect (HOGE) was 1,858 lbs. The pilot also listed the “actual payload” as 1,858 lbs.

The pilot estimated that he had about ¼ to ½ tank of water (about 90-180 gallons) onboard at the time of the accident. He remarked that he estimated water quantity by observing the amount of engine torque required to maintain rotor speed at his desired altitude. Once he reached about 75% and 78% torque he discontinued the water collection. The pilot reported that an updated load calculation was not completed and that he took on less water instead to accommodate for the higher altitude at his destination.

An NTSB computation determined a total helicopter weight, without payload, of 8,741 lbs based on a helicopter-equipped weight of 7,141 lbs, a flight crew weight of 200 lbs, and a fuel weight of 1,400 lbs at water collection. Performance calculations were completed at a pressure altitude of 2,000 ft and a temperature of 30° C, the estimated dipping altitude and temperature at the time the pilot refilled his water tank. According to the helicopter manufacturer, at 75% and 78% torque, the hover in ground effect (HIGE) weight at pickup was 9,965 lbs and 10,280 lb, respectively. The water payload at pickup was calculated at 1,224 lbs at 75% torque and 1,539 lbs at 78% torque. The operating weight at the accident site was computed using this calculated water payload at pickup, along with a pressure altitude of 8,000 ft and a temperature of 20° C, and an estimated total fuel consumption of 120 lbs. At 75% torque the helicopter operating weight would have been 9,845 lbs and at 78% torque the weight would have been 10,160 lbs.

According to the BLR FF HOGE charts, based on the pressure altitude of 8,000 ft and a temperature of 20° C, the helicopter weight limit was 10,000 lbs.

According to the pilot, before the accident flight he had been notified by Air Attack that he would need to perform a water drop over another spot fire. The pilot had sufficient power margin while operating at higher altitudes all day and didn’t feel he needed to recalculate his load before completing this drop.

According to the flight manual supplement,

“The Simplex Fire Attack System is used on the Bell 205A-1, 205B, 212, 412 and 412EP helicopters series for the purpose of fighting fires. The tank system is filled via ground fill or either a 3" standard hover refill pump or optional 5" hover refill pump. The 5" hover pump offers decreased fill times in comparison to the 3" standard hover refill pump. Simplex Fire Attack System allow for independent filling, unloading, and delivery of fire retardant and/or water.”

The supplement also contains delivery instructions that require the operator to “pull and hold the DOORS OPEN switch aft the cyclic control box.” The doors close once the switch is released. A note states that the DOORS OPEN switch must be in the open position to ensure a full release of the water load.

For an emergency jettison the instructions state,

“In the event of an aircraft emergency or if difficulty is experienced in controlling the helicopter, the water load should be dumped immediately using the DOORS OPEN switch on the CCB [cyclic control box]. The pilot should hold the door open for a minimum of 3-5 seconds and visually check that the load has been dumped. If the doors fail to open turn off MASTER switch on CDB [cockpit display box], the doors will remain open until the MASTER switch is turned ON.

There were no historical maintenance records that showed abnormal performance of the Simplex system on the accident helicopter.