Las Vegas, NV, USA
N225JM
Robinson R44
The pilot rented the helicopter to make a local personal flight. Radar data indicated that, after maneuvering around the area of a nearby national conservation, the helicopter flew along a road back toward the airport. The helicopter continued at an altitude between 500 to 700 ft above ground level (agl) for about 30 seconds then radar data ended 1 nautical mile from the accident site. A witness observed the helicopter impact the ravine adjacent to the road and break apart on impact. Ground scar analysis and wreckage fragmentation revealed that the helicopter collided with terrain in a tail-low attitude, consistent with the pilot performing an autorotation before impact. Postaccident examination revealed evidence that the engine was running at the time of impact. The white exhaust signatures were consistent with lean operation. Examination of the engine compartment revealed that one magnet in the main rotor tachometer indicating system was separated from its housing from the yoke assembly; the other magnet assembly remained secured to the yoke assembly. The yoke assembly was not damaged, but there was evidence of slight damage to both senders, consistent with the magnet contacting the senders. With only one magnet installed, the main rotor tachometer rpm would indicate about 50% of the actual rotor rpm and the low rotor rpm horn would sound. It could not be determined if the magnet came free from the housing prior to impact. Examination of the magnet assembly revealed signatures consistent with compliance with a manufacturer service bulletin requiring the use of adhesive to secure the magnets. The helicopter was refueled the morning of the accident, and the fuel was sumped by a pilot receiving instruction and a flight instructor. The fuel samples from the main fuel tank were dirty and they opted to cancel the flight and have a mechanic flush the tanks. The mechanic never flushed the tanks, but the flight instructor reportedly took more samples later in the day until they were clean. When the accident pilot arrived before the flight, he was told that the helicopter had completed maintenance and was informed that an earlier flight was canceled because a pilot had found sediment in the fuel tanks. The accident pilot’s preflight actions could not be determined, but it is likely he would have sumped the tanks and found them to be clean, given that he was aware of an issue earlier in the day. Investigators took samples of the liquid in the gascolator while at the accident site. The color was an orange-yellow and there was some debris in the bowl that displayed a gelatinous consistency; the screen was clear. The remainder of the fuel found in the system was free of contamination. An analysis of the fuel was consistent with that of normal aviation fuel with the presence of iron and brass consistent with that of corrosion. A further examination of the remaining fuel showed the presence of fillers in a polymeric material. The origin of the material found is unknown and the effect, if any, on the helicopter performance could not be determined. The reason the pilot conducted an auto-rotation could not be determined. It is feasible that if the magnet from the rotor tachometer separated inflight, the pilot would hear the magnet contact the airframe, have the low-rotor warning horn sound, the main rotor tachometer rpm would display 50%, and in response he would perform an autorotation. This scenario could not be determined because of the damage incurred to the airframe during the accident sequence. Because there was evidence that the engine was running at the time of impact, it could also not be determined if the fuel contributed to an inflight event that resulted in the pilot’s decision to make an autorotation.
HISTORY OF FLIGHTOn October 23, 2019, at 1553 mountain standard time, a Robinson R44 II Raven, N225JM, was substantially damaged when it was involved in an accident near Las Vegas, Nevada. The airline transport pilot and passenger were fatally injured. The helicopter was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight. The pilot contacted the fixed based operator (FBO) that rented the helicopter in the early afternoon on the day of the accident and asked office personnel if the helicopter was available to rent later that afternoon. One of the schedulers responded that the helicopter was undergoing maintenance, and the pilot stated that he would stop by the office anyway to check if the maintenance was done and put money on his account. The pilot and passenger arrived about 10 minutes later. The pilot asked why the helicopter was in maintenance and the office personnel told him that an earlier flight was canceled because that pilot had found sediment in the fuel tanks. The accident pilot stated that he was happy to wait, and about 20 minutes later, the flight instructor who had canceled the earlier flight called, stating that the maintenance was done, and the helicopter was ready to fly. The pilot and passenger planned to take a 1-hour flight. (see figure 1.) Figure 1: Airport to Accident Site A witness, who was also a pilot, stated that while riding his motorcycle, he initially saw the helicopter in the upper right-corner of his vision at an estimated 100 to 200 feet above ground level (agl) in a nose-up attitude and in a very steep descent angle heading opposite his direction of travel. He estimated that the helicopter was moving about the same speed as the traffic (about 50 mph). He witnessed the helicopter impact the ravine adjacent to the road (about 200 ft ahead of him and 100 ft to the right) and break apart on impact. A review of radar flight track data indicated that the helicopter departed and continued west-southwest toward the Red Rock Retention Basin checkpoint. After clearing the Class Bravo airspace, the returns showed a left 360° orbit over Blue Diamond Road, consistent with the pilot circling over a remote control (RC) airpark and the Desert Sportsman’s Rifle Club. Thereafter, the track was consistent with the pilot loosely following the road around Calico Basin and climbing up to 4,700 ft mean sea level (msl), about 400 ft agl. The helicopter then made a left turn and serval maneuvers over the Red Rock National Conservation Area washes, including a possible touchdown, during which the forward airspeed speed was reduced to 0 kts. After performing serval low-level maneuvers, the track was consistent with the helicopter following Blue Diamond Road toward the north-northeast. The last radar return was at 1553:23 about 1 nautical mile (nm) west-southwest of the accident site. The last 30 seconds of the track data indicated an airspeed of about 100 to 120 kts at an altitude between 500 to 700 ft agl. (see figure 2 below.) Figure 2: Radar Track Data PERSONNEL INFORMATIONThe pilot held an airline transport pilot certificate with a rating for airplane multiengine land, and commercial privileges for airplane single-engine land and rotorcraft-helicopter. According to information compiled from Federal Aviation Administration (FAA) records, as of the date of the accident, he had approximately 15,000 total hours of flight experience. The pilot’s rotorcraft logbook indicated that the pilot began flying helicopters in 2013 with a majority of his earlier experience acquired in a Schweizer helicopter. His last flight was recorded on March 3, 2019, during which he received a 0.9-hour checkout in an R44, including practice autorotations, low rotor rpm recovery, and settling with power. The flight included 6 daytime landings and occurred 234 days before the accident flight. The pilot’s total rotorcraft experience was 352.1 hours, of which 8 flights were in the R44 helicopter, totaling 12.3 hours. The logbook indicated that he had flown the accident helicopter once before on February 8, 2019, for 1.5 hours during which he flew from North Las Vegas to Henderson, Nevada, and back; there were no other recorded helicopter flights from North Las Vegas. A logbook endorsement dated July 2016 stated that the pilot had completed the awareness training in accordance with paragraphs "(b)(2)(ii)(a-d) " of Section 2 of Special Federal Aviation Regulation (SFAR) No. 73. The currency requirements provided in the SFAR state that no person may act as pilot-in-command of an R44 helicopter carrying passengers unless the pilot in command has met the recency of flight experience requirements of §61.57 in an R44. In pertinent part, § 61.57 (a)(1) states that “Except as provided in paragraph (e) of this section, no person may act as a pilot in command of an aircraft carrying passengers … unless that person has made at least three takeoffs and three landings within the preceding 90 days and -(i) The person acted as the sole manipulator of the flight controls; and(ii) The required takeoffs and landings were performed in an aircraft of the same category, class, and type (if a type rating is required)…” The exceptions did not pertain to the accident flight because the pilot was not conducting the flight operation under a part 119 certificate holder. AIRCRAFT INFORMATIONThe Robinson R44 Raven II helicopter was manufactured in 2005 and was equipped with its original Lycoming IO-540-AE1A5 engine. The tachometer time at the accident site was 3,231.3 hours. According to inspection and maintenance records, the last 50-hour engine inspection was completed on October 08, 2019, at a tachometer time of 3,195.4 hours, 35.9 hours before the accident; the last 100-hour airframe inspection was completed on September 28, 2019, at a total time of 3,144.5 hours. Governor and Tachometer System The collective control for the accident helicopter was conventional and included a twist grip throttle. When the collective control is moved upward, the engine throttle is opened automatically by an interconnecting linkage. The helicopter was equipped with an engine governor system, which sensed engine rpm and applied corrective input forces to the throttle to maintain engine rpm as needed. The governor system comprised a solid-state electronic controller, which determined engine rpm from the tachometer points in the engine's right magneto. When the governor sensed the need to adjust engine rpm, it activated a motor which drove the throttle directly. The governor system was designed to assist the pilot in controlling the rpm in the normal operating range. It may not prevent over- or under-speed conditions generated by aggressive flight maneuvers. The helicopter was equipped with one electronic dual (engine and rotor) tachometer. The sensor for the engine tachometer is the same set of magneto breaker points used by the governor. The sensor for the rotor tachometer is an electronic Hall effect device, which senses passage of two magnets attached to the main rotor gearbox input yoke assembly. (see figures 3 and 4 below.) Robinson personnel reported that, with only one magnet installed, the main rotor tachometer rpm would indicate about 50% of the actual rotor rpm and the low-rotor rpm horn would sound. The normal rotor/engine rpm is 102% on the tachometer and the lowest numeric marking is “50,” with two graduated lines beneath. Figure 3: Rotor Tachometer Assembly Picture 4: Location of Rotor Tachometer Assembly Low Rotor RPM Recovery Procedure According to the R44 Pilot’s Operating Handbook (POH), the recommended procedure to recover from a low rotor rpm warning condition (warning horn and caution light) was as follows: To restore rpm, lower collective, roll throttle on and, in forward flight, apply aft cyclic. According to Robinson, lowering the collective lever will reduce the power required by the rotors to aid the recovery of rotor rpm; however, in the R44 helicopter, the correlator will decrease the throttle when the collective is lowered and reduce engine rpm (by a few percent) unless the pilot or rpm governor system rotates the twist grip to roll throttle on. AIRPORT INFORMATIONThe Robinson R44 Raven II helicopter was manufactured in 2005 and was equipped with its original Lycoming IO-540-AE1A5 engine. The tachometer time at the accident site was 3,231.3 hours. According to inspection and maintenance records, the last 50-hour engine inspection was completed on October 08, 2019, at a tachometer time of 3,195.4 hours, 35.9 hours before the accident; the last 100-hour airframe inspection was completed on September 28, 2019, at a total time of 3,144.5 hours. Governor and Tachometer System The collective control for the accident helicopter was conventional and included a twist grip throttle. When the collective control is moved upward, the engine throttle is opened automatically by an interconnecting linkage. The helicopter was equipped with an engine governor system, which sensed engine rpm and applied corrective input forces to the throttle to maintain engine rpm as needed. The governor system comprised a solid-state electronic controller, which determined engine rpm from the tachometer points in the engine's right magneto. When the governor sensed the need to adjust engine rpm, it activated a motor which drove the throttle directly. The governor system was designed to assist the pilot in controlling the rpm in the normal operating range. It may not prevent over- or under-speed conditions generated by aggressive flight maneuvers. The helicopter was equipped with one electronic dual (engine and rotor) tachometer. The sensor for the engine tachometer is the same set of magneto breaker points used by the governor. The sensor for the rotor tachometer is an electronic Hall effect device, which senses passage of two magnets attached to the main rotor gearbox input yoke assembly. (see figures 3 and 4 below.) Robinson personnel reported that, with only one magnet installed, the main rotor tachometer rpm would indicate about 50% of the actual rotor rpm and the low-rotor rpm horn would sound. The normal rotor/engine rpm is 102% on the tachometer and the lowest numeric marking is “50,” with two graduated lines beneath. Figure 3: Rotor Tachometer Assembly Picture 4: Location of Rotor Tachometer Assembly Low Rotor RPM Recovery Procedure According to the R44 Pilot’s Operating Handbook (POH), the recommended procedure to recover from a low rotor rpm warning condition (warning horn and caution light) was as follows: To restore rpm, lower collective, roll throttle on and, in forward flight, apply aft cyclic. According to Robinson, lowering the collective lever will reduce the power required by the rotors to aid the recovery of rotor rpm; however, in the R44 helicopter, the correlator will decrease the throttle when the collective is lowered and reduce engine rpm (by a few percent) unless the pilot or rpm governor system rotates the twist grip to roll throttle on. WRECKAGE AND IMPACT INFORMATIONThe accident site was located in desert terrain about 10 nm from the departure airport on a bearing of 250°. The wreckage was found distributed in a ravine over a 200-ft distance on a median magnetic heading of about 070°. The ravine and debris field ran parallel to the road and was located about 4 to 5 ft below the pavement. The first identified area of impact was an approximate 5-inch line (oriented parallel to the road) of scraping and maroon-colored paint transfer across a rock and orange torque stripe buried in the dirt before the rock. Adjacent to that line was another parallel line of paint transfer that was red in color. The orientation and colors were consistent with the tail rotor guard and tailskid making contact first, indicative of a nose-high attitude at the time of impact. Airframe and Engine The mixture control was in the full-rich position. The collective was in a full-up position and the collective friction bolt center was at the top of the slider slot. The pilot’s throttle twist grip was in a position close to full off (idle). Examination of the control systems revealed no evidence of pre-impact mechanical malfunction or failure that would have precluded normal operation. Rotational signatures on the aft surface of the engine cooling fan, starter ring gear and oil cooler, alternator, and the belt tension actuator vertical tube surfaces were consistent with the engine producing power at the time of impact. An external visual examination of the engine revealed crush damage to the bottom of the crankcase, with the majority of damage to the oil pan. The spark plugs were removed. No mechanical damage was noted and the electrodes and posts exhibited a light, white ash coloration, which according to the Lycoming representative, was consistent with very lean operation(s). The crankshaft was rotated by hand utilizing the ring gear. The crankshaft rotated freely and easily in both directions. "Thumb" compression was observed in proper order on all six cylinders. The valve train operated in proper order, and appeared free of any pre-mishap mechanical malfunction. Uniform lifting action was observed at each rocker assembly. Clean, uncontaminated oil was observed at all six rocker box areas. Mechanical continuity was established throughout the rotating group, valve train, and accessory section during hand rotation of the crankshaft. The cylinder combustion chambers were examined through the spark plug holes using a lighted borescope. The combustion chambers remained mechanically undamaged, and there was no evidence of foreign object ingestion. The valves were intact and undamaged. There was no evidence of valve-to-piston-face contact. The piston faces all displayed a whitish coloration and the valve faces were white and orange, consistent with a lean operation. White residue/soot was seen throughout the remainder of the exhaust system. The sides of the piston heads were dark black in color and the rings displayed dark discoloration. The ignition harnesses from both magnetos to their respective spark plugs remained intact. The magnetos were secured to their respective mounting pads. The right magneto was timed at 20°; the left magneto was at 18°. Removal of the right magneto revealed that the bearing cage had broken; the broken piece was found in the oil sump. The magnetos were put on a test bench; the left magneto operated normally and the right magneto vibrated, but operated normally with even spark at each post. Both magnetos were rotated by hand and moved freely. It could not be determined the amount of vibration the engine would have been subjected to as a result of the magneto bearing cage being broken. Rotor Tachometer System Examination of the engine compartment revealed that one magnet from the main rotor tachometer indicating system was separated from its housing on the yoke assembly; the magnet was located on the fuselage frame near the firewall. Both the housings showed a color consistent with a dark residue and a yellow/orange mark was on both housings and senders. (see figure 5 below.) The yoke assembly was not damaged. Figure 5: Magnet Housing on Yoke Assembly The National Transportation Safety Board Materials Laboratory completed an examination of the yoke, magnet assembly, and senders. Examination of the damaged magnet housing revealed that the deformation and fracture to the magnet housing was not consistent with that of impact directly with the magnet housing body. The fractured side exhibited deformation consistent with an object pushing from the inside of the housing radially outwards through the cylindrical wall. The intact side of the magnet housing did not exhibit deformation or contain any witness marks consistent with a strike. Deformation was also observed in the magnet housing perpendicular to its direction of motion, consistent with an internal force pushing through the magnet housing side wall. There was orange residue in a shape consistent with a circular outline on the exterior of the magnet housing’s cylindrical wall. (see figures 6 and 7 below.) There were additional areas on the open end of the magnet housing’s
An undetermined inflight event that resulted in the pilot performing an autorotation to uneven terrain for reasons that could not be determined due to the extent of impact damage.
Source: NTSB Aviation Accident Database
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