History of Flight
On October 23, 2019, at 1553 mountain standard time, a Robinson R44 II Raven helicopter, registration N225JM, was involved in an accident near Las Vegas, Nevada. The helicopter sustained substantial damage, and the airline transport pilot and passenger were fatally injured. The flight was conducted as a Title 14 Code of Federal Regulations Part 91 personal flight.
The pilot contacted the fixed based operator (FBO) that rented the helicopter in the early afternoon to inquire about availability. The helicopter was undergoing maintenance due to sediment found in the fuel tanks during a previous flight. The pilot arrived with the passenger and waited. About 20 minutes later, the maintenance was reported complete, and the helicopter was ready for a planned 1-hour flight.
A witness, also a pilot, observed the helicopter in a nose-up attitude and steep descent at an estimated 100-200 feet above ground level. The witness estimated the helicopter's speed at about 50 mph and saw it impact a ravine adjacent to the road, breaking apart on impact.
Review of radar data showed the helicopter departed and flew west-southwest, performed maneuvers including orbits and low-level flight over the Red Rock National Conservation Area, and then followed Blue Diamond Road north-northeast. The last radar return was at 1553:23, about 1 nautical mile from the accident site. The final 30 seconds of data indicated an airspeed of 100-120 knots at 500-700 feet agl.
Personnel Information
The pilot held an airline transport pilot certificate with ratings for airplane multiengine land and commercial privileges for airplane single-engine land and rotorcraft-helicopter. He had approximately 15,000 total flight hours. According to his rotorcraft logbook, he began flying helicopters in 2013 and had 352.1 total rotorcraft hours, with 12.3 hours in the R44, including a 0.9-hour checkout 234 days before the accident. He had flown the accident helicopter once before, for 1.5 hours in February 2019.
A logbook endorsement from July 2016 indicated completion of awareness training per SFAR No. 73. The pilot's recency of flight experience did not meet the requirements of 14 CFR 61.57 for carrying passengers in an R44, as he had not performed three takeoffs and landings in the preceding 90 days.
Aircraft Information
The helicopter was a 2005 Robinson R44 Raven II with a Lycoming IO-540-AE1A5 engine. The tachometer time at the accident was 3,231.3 hours. The last 50-hour engine inspection was on October 8, 2019, and the last 100-hour airframe inspection on September 28, 2019.
The helicopter was equipped with a conventional collective control with twist-grip throttle and an engine governor system. The governor used tachometer points from the right magneto to adjust throttle. The helicopter had one electronic dual tachometer for engine and rotor rpm. The rotor tachometer sensor used Hall effect devices sensing two magnets on the main rotor gearbox yoke. Robinson reported that with only one magnet installed, rotor rpm indication would read about 50% of actual and the low-rotor rpm horn would sound.
The R44 Pilot's Operating Handbook recommended for low rotor rpm recovery: lower collective, roll throttle on, and in forward flight, apply aft cyclic. Robinson noted that lowering collective reduces power required but the correlator decreases throttle unless the pilot or governor rotates the twist grip to roll throttle on.
Wreckage and Impact Information
The accident site was 10 nm from the departure airport at a bearing of 250°, in desert terrain. Wreckage was distributed over 200 ft in a ravine parallel to the road. First impact marks included paint transfer consistent with the tail rotor guard and tailskid contacting the ground, indicating a nose-high attitude.
The mixture control was full-rich, collective full-up, and pilot's throttle twist grip near full-off. Control systems showed no pre-impact mechanical malfunction. Rotational signatures on engine components indicated power at impact.
Engine examination revealed crush damage to the crankcase bottom. Spark plugs had light white ash coloration, consistent with lean operation. Crankshaft rotated freely with compression on all cylinders. Valve train operated normally. Combustion chambers showed no damage, with whitish piston faces and orange valve faces, also consistent with lean operation. The right magneto had a broken bearing cage; the left magneto operated normally. It could not be determined the vibration level from the broken bearing cage.
Examination of the rotor tachometer system found one magnet separated from its housing on the yoke assembly. The magnet was located on the fuselage frame. The housing showed deformation consistent with an internal force pushing outward. Orange residue resembling paint was present, consistent with a marker for compliance with Service Bulletin 86, which required adhesive application. However, the aircraft records did not contain entries related to the service bulletin. Analysis of residue suggested it was similar to cured or degraded Loctite adhesive.
Tests and Research
Fueling records showed the accident helicopter was fueled twice the day before the accident and once on the morning of the accident, with no reported contaminants. The fuel truck had been refilled and tested clean.
The NTSB database review noted two previous accidents involving magnet separation in Robinson helicopters: ERA17LA163 (April 2017) and CEN13LA194 (March 2013). Both involved separation of a magnet from the rotor tachometer assembly, leading to low rotor rpm warnings and subsequent autorotations. In CEN13LA194, the probable cause was total loss of engine power due to rapid throttle change during autorotation, with contributing factors including the instructor's aft cyclic input. Robinson issued Service Bulletin 86 after that event.