History of Flight
On August 25, 2017, about 1850 Pacific daylight time, a Robinson R-44 Raven II helicopter, registration N61NM, was substantially damaged when it encountered a dynamic rollover during a forced landing in Eldorado Hills, California. The commercial pilot and his passenger received minor injuries. The helicopter was registered to A M Helicopter Services, LLC and operated by a private individual as a personal flight under 14 CFR Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight that departed Auburn Municipal Airport (AUN) at 1830.
The pilot, who also held an airframe and powerplant mechanic certificate, flew the helicopter once in the traffic pattern and then taxied to the fuel island. After adding 20 gallons of 100 low lead aviation gasoline, the pilot and his passenger departed. The magnetos were checked prior to departure, but the pilot did not recall if he allowed the rpm to stabilize. They flew near a soccer field for photographs, then to a nearby lake for a practice autorotation. During the maneuver, both occupants heard the low rotor rpm horn and saw the annunciator light. The pilot increased engine power, raising the rpm.
They then changed course to a friend's home. The pilot decelerated into an in-ground effect hover over the backyard, where downwash blew debris into a pool. Despite the friend signaling to land on a concrete block, the pilot chose an alternate site. He flew backwards into and out of ground effect over a solar panel array. The main rotor rpm decayed, and the low rotor rpm horn activated. The pilot applied full power, achieving 28 in Hg manifold pressure and 96% rotor rpm, but the helicopter began to descend. Lowering the collective restored normal rpm. After a 360° right pedal turn to search for another landing site, the helicopter began sinking again. The pilot decided to land on the solar panels. As the left skid impacted a panel, the passenger exited and ran to a grassy area. The helicopter then ascended about 20 ft before descending toward the grassy area. The right skid contacted the ground, followed by the left, resulting in a dynamic rollover, and the helicopter came to rest on its left side.
The property owner reported that the passenger had asked permission to land about 4 minutes before the helicopter arrived. He observed single puffs of smoke every 3-4 seconds. He directed the pilot to the pool deck, but the helicopter entered a hover over foliage, turned 90° east while sliding left, emitting more smoke. After ascending over the solar panels, it entered a pedal turn and descended. It briefly reappeared, turned southeast with a constant stream of very dark gray smoke, then settled out of view. The engine sounded continuous throughout.
The passenger stated he did not hear an engine or rotor harmonic during the rollover. Neither occupant observed engine roughness.
Personnel Information
The pilot had accumulated 3,985 total flight hours and 66.5 hours in the accident helicopter make and model. He estimated 3 hours in the same make and model within the 90 days preceding the accident and about 500 total hours in Robinson R-22s, with none in the last 90 days.
Aircraft Information
The helicopter was manufactured in 2006 and registered to A M Helicopter Services on May 20, 2008. It was powered by a Lycoming IO-540-AE1A5, a direct drive, air cooled, 260 hp engine. The most recent 100-hour airframe inspection was completed on May 21, 2017, at 1,991.3 flight hours. At the accident, total time was 2,095 flight hours.
The engine's most recent 100-hour inspection was by IA Maintenance in Woods Cross, Utah. The mechanic recorded a differential compression check, spark plug cleaning and gapping, magneto and tachometer inspection, and magneto timing check, and compliance with Lycoming Service Bulletin 301B. The previous 100-hour inspection record (January 1, 2017) was identical except for hobbs times. The owner reported no top overhaul had been completed.
The owner leased the helicopter to Utah Helicopters for 2 years beginning in 2015 for flight instruction. A flight school representative reported accumulating about 500 hours. It was returned on August 21, 2017, with a report from the ferry pilot that the helicopter was underpowered—a description not communicated to the accident pilot.
The two ferry pilots, who had about 300 hours in the helicopter with the school, commented it had been underpowered since receipt, but it passed inspections, so they managed the deficiency.
Meteorological Information
The 1855 recorded weather at AUN (13.5 nm north) included wind from 250° magnetic, calm, visibility 10 statute miles, clear skies, temperature 32°C, dew point 26°C, and altimeter 29.86 inches of mercury.
Wreckage and Impact Information
Postaccident examination revealed substantial damage to main rotor blades and cockpit. Scuff marks and longitudinal scoring were present on the nose, belly, chin, and belly. The left roof, door frames, and fuel tank forward edge sustained impact damage; the left windshield was shattered. Minor dents were on tailcone bay nos. 4 and 5. The strobe light lens was shattered; left navigation antenna was damaged. The upper vertical stabilizer had leading edge damage; the horizontal stabilizer had trailing edge damage. The tail skid was bent upward; the tail rotor guard was broken during recovery.
Flight control continuity was confirmed from the cockpit to the main and tail rotors. All three main rotor servos operated smoothly. One main rotor blade displayed upward bowing near the tip, chordwise creasing, and bending opposite rotation; tree residue was on the leading edge. The other main rotor blade showed similar bowing, creasing, and a 5-foot section of afterbody separated from the spar; tree residue was on the leading edge and lower surface. Both tail rotor blades remained attached, with dents, scuff marks, and tree residue.
The main and auxiliary fuel tanks had no breaches or leaks; caps were secure; vent tubes clear. The gascolator screen had trace debris; fuel odor and color were consistent with 100LL. The auxiliary fuel pump did not engage when tested.
Engine rotational continuity was established; light compression was felt on all cylinders. Ignition harness leads showed arcing; leads to cylinders 3 and 5 were loose; the cylinder 1 upper plug rim had corrosion. Spark plugs displayed excessive contamination with carbon deposits and debris causing electrode bridging, classified as severely fouled. Lower plugs to cylinders 1, 3, and 5 showed oil fouling consistent with the helicopter's resting position.
Magneto timing measured 10° before top dead center, versus the manufacturer's specification of 20° BTDC.
During an engine run, the engine idled roughly at 64% for 2 minutes with gray smoke; at 100% rpm it continued to run rough. A magneto check at 75% rpm showed drops to 61% on left and 55% on right. Cylinder 5 was cooler; cylinder 3 intake pipe was loose. Compression tests at 80 psi yielded: no.1: 28, no.2: 34, no.3: 52, no.4: 38, no.5: 36, no.6: 54. Air leaked from the exhaust during each test. A second run with clean spark plugs gave similar results.
An examination of intake valve movement revealed that both intake valves for cylinders 5 and 6 extended only about one-third of normal travel. A visual inspection of the camshaft showed severe wear and spalling on the intake cam lobes for cylinders 5 and 6.
Additional Information
Two instructors from Utah Helicopters reported the performance issues during company meetings and to mechanics. The company did not employ a full-time mechanic and used contractors. A maintenance flight typically revealed the same issues. One instructor was told by a mechanic that the engine was "old and tired" and unlikely to produce more power. The instructors managed the problem by flying with reduced load and at lower terrain elevations.
The mechanic who performed the most recent service performed about 12 inspections per year to maintain his inspection authorization. He did the work after hours or on weekends, as he was employed full-time by a U.S. government agency, not as a mechanic. He normally verified valve movement via compression check rather than visual inspection of rocker arms. He had not complied with Service Bulletin 301B in recent years, as it was not required and the owner instructed no additional maintenance unless necessary.
Lycoming Service Bulletin 301B (1977) mandates that rocker box covers be removed and the engine rotated every 400 hours to verify normal valve lift. FAA Part 43 Appendix D requires a cylinder compression check during 100-hour inspections. FAA AC 43.13-1B states that a cylinder with less than 60/80 on differential test gauges on a hot engine must be removed and inspected.