N314

HISTORY OF FLIGHTOn August 24, 2020, about 1747 Pacific daylight time, a Kaman K-1200 helicopter, N314, was substantially damaged when it was involved in an accident near Pine Grove, Oregon. The pilot was fatally injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 133 external load flight.

The helicopter was operated under an exclusive-use contract with the United States Forest Service (USFS) and had been conducting water bucket/fire suppression activities for the White River fire at Mt. Hood National Forest, Oregon. The air attack controller, who was in radio contact with the pilot, reported that the pilot indicated that he needed to return to the heliport to refuel after “one more bucket.” The pilot provided no further transmissions to the air attack controller. About 15 minutes later, the air attack controller contacted dispatch and learned that the helicopter had not returned to the heliport. The air attack controller then flew to the dip site, where he observed the helicopter lying on its right side in the river at the dip site. No “mayday” radio call was received from the accident pilot.

Onboard GPS instrumentation revealed that, about 1745 on the day of the accident, the helicopter was about 0.75 miles southwest of the accident dip site. The helicopter returned to the dip site and began to slow down and descend over the dip site. The last recorded data point was about 138 ft above ground level at 0 knots and was about 15 ft from the location of the main wreckage; see figure 1.

Figure 1. Flightpath showing the helicopter’s height above ground level and speed.

Note: The spacing between each vertical line represents a 1-second interval. PERSONNEL INFORMATIONAccording to a family member, the pilot had about 10 years of flight experience in the helicopter make and model, and he performed the “more difficult operations” for the operator. AIRCRAFT INFORMATIONThe K-1200 helicopter had two counterrotating, side-by-side, intermeshing rotors with two blades per rotor (for a total of four blades). The rotors were out of phase by 90° and were tilted outward to allow each blade to clear its opposing rotor hub. The two rotor systems were mounted to, and driven by, a common transmission. When viewed from above, the left rotor system turned counterclockwise, and the right rotor system turned clockwise. The two blades for each rotor system comprised a matched set that was balanced at the helicopter manufacturer’s factory; each set had an “A” blade (colored white at the tip) and a “B” blade (colored red at the tip). Figure 2 shows the accident helicopter. The helicopter was not equipped with, or required to be equipped with, a flight data recorder.

Figure 2. Accident helicopter (Source: Central Copters).

The K-1200 rotor system used servo-flaps to control rotor blade pitch changes. The Kaman K-1200 Maintenance and Servicing Instructions document states the following about servo flaps:

A servo-flap is mounted on each blade near the 3/4 radius and is controlled by [control] rods which transfer conventional cockpit flight control inputs through the azimuth assemblies to each servo flap. The servo-flap controls the pitch of the rotor blade and acts as an aerodynamic stabilizer. Because the servo-flap uses energy drawn from the air stream to twist the blade, control forces need only be high enough to deflect the small servo-flap.

The accident helicopter was maintained under the manufacturer’s approved airworthiness inspection program. Recurring inspections for the rotor blade servo flaps in the K-12 maintenance manual included the preflight inspection and the 100 hour/annual or zone one progressive inspection. A review of the maintenance logbooks revealed that the last zone one inspection occurred on February 25, 2020. AIRPORT INFORMATIONThe K-1200 helicopter had two counterrotating, side-by-side, intermeshing rotors with two blades per rotor (for a total of four blades). The rotors were out of phase by 90° and were tilted outward to allow each blade to clear its opposing rotor hub. The two rotor systems were mounted to, and driven by, a common transmission. When viewed from above, the left rotor system turned counterclockwise, and the right rotor system turned clockwise. The two blades for each rotor system comprised a matched set that was balanced at the helicopter manufacturer’s factory; each set had an “A” blade (colored white at the tip) and a “B” blade (colored red at the tip). Figure 2 shows the accident helicopter. The helicopter was not equipped with, or required to be equipped with, a flight data recorder.

Figure 2. Accident helicopter (Source: Central Copters).

The K-1200 rotor system used servo-flaps to control rotor blade pitch changes. The Kaman K-1200 Maintenance and Servicing Instructions document states the following about servo flaps:

A servo-flap is mounted on each blade near the 3/4 radius and is controlled by [control] rods which transfer conventional cockpit flight control inputs through the azimuth assemblies to each servo flap. The servo-flap controls the pitch of the rotor blade and acts as an aerodynamic stabilizer. Because the servo-flap uses energy drawn from the air stream to twist the blade, control forces need only be high enough to deflect the small servo-flap.

The accident helicopter was maintained under the manufacturer’s approved airworthiness inspection program. Recurring inspections for the rotor blade servo flaps in the K-12 maintenance manual included the preflight inspection and the 100 hour/annual or zone one progressive inspection. A review of the maintenance logbooks revealed that the last zone one inspection occurred on February 25, 2020. WRECKAGE AND IMPACT INFORMATIONThe dip site, where the helicopter came to rest, was lined on three sides by trees with a height of about 100 ft. No evidence indicated an in-flight impact with any of the trees surrounding the accident site.

The entire airframe was found at the accident site, and no evidence indicated an in-flight fuselage breakup. The nose of the helicopter had crushed aft and inward, which was consistent with contacting the river in an inverted attitude. The tailboom exhibited deformation on its underside immediately aft of the horizontal stabilizer, resulting in downward bending of the aft portion of the tailboom. The left horizontal stabilizer remained installed. The right horizontal stabilizer had fractured and separated but was found next to its normally installed location. The main and nose landing gears remained attached to the fuselage. The vertical fin remained attached to the tailboom, but its top end was impact damaged.

The 140-ft-long line, which remained attached to the cargo hook of the helicopter, had wrapped around the fuselage in a direction consistent with the fuselage rolling to the left around the long line (or, conversely, the long line wrapping above and to the right of the fuselage). The water bucket remained attached to the end of the long line and was found about 40 ft upstream of the accident site. The long line was not damaged, and the water bucket sustained minor damage.

The engine and transmission remained attached in the helicopter. Both left and right transmission pylons had separated from the main transmission center housing and were found adjacent to the main transmission. Examination of the engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

Examination of the rotor blades found damage that included (but was not limited to) root end fractures on the left main rotors and contact marks on the left and right rotors. All blade dampers separated from their respective rotor systems; one was recovered. Both the left and right blade sets exhibited damage consistent with the blades leading and lagging beyond the stops.

Flight control continuity was established for the cyclic, collective, and pedal controls. The control tubes and bellcranks from the cockpit controls to the azimuth control installation exhibited impact fractures but no evidence of disconnection. The left and right azimuth controls remained attached to the lower side of the main transmission.

Left Rotor System

The white rotor blade fractured into three sections and separated from the hub near the root ends. The largest section of the white blade was found in a wooded area about 560 ft from the main wreckage. The tip section was located near the largest blade section and exhibited significant deformation in multiple locations. The inboard section of the white blade remained attached to its rotor head grip.

The white blade’s servo flap spar remained attached to the blade, but the servo-flap afterbody had completely fractured and separated from the spar and was found about 192 ft from the main wreckage. Both the upper and lower fractures of the servo-flap afterbody were nearly straight in the spanwise direction.

The red blade fractured into two locations. Most of the red blade was found in a wooded area about 500 ft from the main wreckage. The tip section was found in the wooded area about 570 ft from the main wreckage. The underside of the blade exhibited a dark-colored triangular-shaped rub mark, similar in color to the leading-edge coating of the rotor blades, as well as impact marks on the spar, core, and skin, consistent with a scuff and blunt impact marks along the leading edge of the right white blade. The inboard section of the left red blade remained attached to its rotor head grip. The red blade servo flap was whole and remained attached to the blade.

Right Rotor System

The right white blade remained attached to the rotor head but fractured and partially separated in four locations. Most of the right white blade was found adjacent to the main wreckage. The right white servo flap was whole and remained attached to the blade.

The right red rotor blade fractured in one location, with most of the blade found about 81 ...