Boise, ID, USA
N8366F
Hughes 369D
The commercial pilot, who had 900 hours PIC flight time in the make/model, and an FAA check pilot, who had 40 hours PIC flight time in the make/model, departed on a Part 135 check flight in the McDonnell Douglas (Hughes) 369D rotorcraft. After returning to the Boise airport, the commercial pilot (examinee in the left seat) transferred control of the aircraft to the check pilot (right seat) who then demonstrated a simulated 180-degree autorotation. After the check pilot rolled off power, the GEN OUT caution light illuminated followed by the ENG OUT warning light. The check pilot noted rotor RPM in the green but decelerating engine RPM, and the commercial pilot reported that he felt the check pilot's flare was premature. The rotorcraft landed hard during which time the main rotor blades flexed down impacting and severing the tailboom. Post-crash examination revealed that the left and right seat throttle/collective controls to the engine fuel control unit had been misrigged, and a test run of the engine confirmed a flameout condition when the right seat throttle was retarded to the idle position. A review of the rotorcraft's maintenance log showed that the right seat controls had been installed two days previous and signed off as "all rigging found to be within limits." The McDonnell Douglas MD500D Rotorcraft Flight Manual discusses throttle rigging in the Normal Procedures Section noting that a throttle rigging check must be performed prior to autorotation training, and the check must be performed on both left and right seat throttle controls if dual controls are installed. The Rotorcraft Flight Manual also provided a warning that "Misrigging of the throttle control may result in inadvertent flameout during rapid closing of the twistgrip to the ground idle position."
On December 24, 2002, at 1050 mountain standard time, a McDonnell Douglas (Hughes) 369D rotorcraft, N8366F, registered to Silverhawk Aviation LLC, operated by Pathfinder Helicopters Inc., and being flown by a commercial pilot and a Federal Aviation Administration (FAA) check pilot, sustained substantial damage during a hard landing following a loss of power during the recovery phase of a simulated autorotation landing. The accident occurred approximately 1,000 feet east of the threshold of runway 28L at the Boise Air Terminal, Boise, Idaho. Neither pilot was injured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was a Federal Air Regulations (FAR) Part 135.293 VFR check ride being conducted by the check pilot on the commercial pilot, was operated under 14 CFR 91, and originated at Boise at 1000. The commercial pilot (left seat examinee), who had 900 hours pilot in command time in the accident rotorcraft make/model, reported that after operating in the practice area, he and the FAA check pilot returned to the Boise airport and continued the check flight, executing a number of simulated autorotations. He then executed a simulated 180-degree autorotation and at its conclusion, and at the check pilot's request, control of the helicopter was transferred from the commercial pilot to the check pilot. The check pilot then set up for a demonstration of a simulated 180-degree autorotation. The commercial pilot further reported that about 90 degrees into the autorotation he observed the "GEN OUT" caution light followed by the "ENG OUT" warning light and commented that the check pilot had good control of the airspeed and rotor RPM. He noted that the check pilot completed the last 90 degrees of turn arriving approximately 200 feet above ground. The check pilot then initiated a flare, which the commercial pilot felt was premature; followed by a collective pitch pull, which he felt was initiated at a higher than normal altitude. Upon touchdown the main rotor blades contacted and severed the tail boom and the helicopter came to rest in an upright attitude. The check pilot (right seat), who had 40 hours total/pilot in command time in the accident rotorcraft make/model, reported that upon their return to the Boise airport he commenced a demonstration of a simulated 180-degree autorotation and initially noted the illumination of the "GEN OUT" caution light. The check pilot further reported that the rotor RPM was still in the green (arc), but engine RPM was observed spooling down shortly before ground contact. Upon touchdown the main rotor blades flexed downward impacting the helicopter's tail boom. Post-crash examination of the aircraft and engine revealed no mechanical malfunctions or discontinuities with the exception of a misrigging condition between the left and right seat throttle/collective controls and the engine fuel control unit. A test run of the engine was performed starting with a successful engine start. The engine was then stabilized at 100% N2 and the pilot's throttle (left seat position) was abruptly reduced to the idle detent. The engine decelerated and then stabilized at 63% N1. The right seat throttle was then retarded to the idle detent and the engine then flamed out (refer to Attachment RR-I). A review of the helicopter's logs revealed that on December 22, 2002, a number of maintenance items were signed off. Specifically, the following entry was noted: "Installed dual controls per Hughes Maintenance manual section 67-10-00 and 67-20-00. Controls freedom of travel found to be good. All rigging found to be with in limits of Hughes Maintenance manual section 67-10-00 and 67-20-00." The log entry was concluded with a reference to a flight test performed (refer to Attachment RR-II). The McDonnell Douglas MD500D Rotorcraft Flight Manual discusses throttle rigging in the Engine Runup Section of the Normal Procedures Section. Specifically, the section states: *THROTTLE RIGGING CHECK NOTE: "If the flight will involve rolling the twistgrip to the ground idle position while airborne (Autorotation training, maintenance test flight, etc.) this check must be performed even thought [sic] it may not be the first flight of the day." The procedure also contains the following "If dual controls are installed, repeat procedure using copilot's twistgrip." (Refer to Attachment RFM-I). The McDonnell Douglas MD500D Rotorcraft Flight Manual also addressed this issue in the same section under "Practice Autorotations with the following warning: WARNING: Perform throttle rigging check prior to attempting practice autorotations (paragraph 4-4). Misrigging of the throttle control may result in inadvertent flameout during rapid closing of the twistgrip to the ground idle position." (Refer to Attachment RFM-II).
The failure of the operator's maintenance personnel to properly rig the left/right seat twistgrip throttles to the engine fuel control, the pilot in command's failure to adhere to the rotorcraft flight manual, and the check pilot's premature flare during the autorotation resulting in a hard landing.
Source: NTSB Aviation Accident Database
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