Myrtle Beach, SC, USA
N828RD
ROBINSON HELICOPTER R44
The commercial pilot and two passengers departed in the helicopter for a commercial air tour flight. The pilot reported that, shortly after takeoff, the helicopter started shaking like a "minor kick," which he thought might be due to a stuck engine valve. He immediately radioed the operator and requested that maintenance personnel meet the flight after the tour ended. He chose to continue the tour and attempted to maintain about 70 knots with the engine operating at 25 inches manifold pressure, which resulted in a descent rate of 300 ft per minute. When the helicopter was near the helipad location, company personnel reported seeing white smoke trailing from the helicopter, and the pilot noted that the alternator light was on. When the pilot started to slow the descent, the low rotor rpm horn sounded, and the engine rpm spiked. After realizing the helicopter would not be able to reach the helipad, the pilot turned the helicopter parallel to the slope of an adjacent field and fully pulled the collective pitch to cushion the landing, but the helicopter landed hard. Postaccident examination of the engine revealed that the No. 5 cylinder exhaust valve pushrod and housing were fractured, which allowed about 2.5 quarts of engine oil to drain from the engine; the oil had coated the V-belts that transmitted power from the engine to the main rotor system. The pushrod and housing likely failed due to a stuck exhaust valve that occurred at engine startup and then became unstuck once the engine was warmed up. The subsequent release of oil onto the V-belts, of which the pilot was unaware, likely resulted in the V-belts slipping and the main rotor rpm decreasing. A service bulletin recommending a procedure every 300 hours or earlier to determine exhaust valve and guide condition was last accomplished on the helicopter 298.3 hours since overhaul.
On July 24, 2017, about 1316 eastern daylight time, a Robinson R44, N828RD, registered to KHGK LLC, operated by Helicopter Solutions, Inc., dba Helicopter Adventures, was substantially damaged during a hard landing near Myrtle Beach, South Carolina. The commercial pilot and 2 passengers were not injured. The helicopter was operated under the provisions of 14 Code of Federal Regulations Part 91 as a commercial air tour flight, on a company visual flight rules flight plan. Visual meteorological conditions prevailed at the time of the local flight, which originated about 1310 from the operator's facility.The pilot stated that after departure while on the Boardwalk Adventure tour flight when near the Sky Wheel, the helicopter started shaking like a "minor kick" which he initially thought was a stuck valve. Near that location he made a radio call to advise company personnel that a mechanic would be needed to meet the flight. He elected to continue the tour, and attempted to maintain about 70 knots with the engine operating at 25 inches manifold pressure (he did not report engine rpm), which resulted in a descent rate of 300 feet-per-minute. When he was near the departure helipad location, company personnel reported seeing white smoke trailing the helicopter, and the pilot noticed the alternator light was on. He started pulling power to slow the descent, but the low rotor rpm horn came on and the engine rpm spiked. Realizing he was unable to reach the intended helipad, he turned the helicopter with the slope of an adjacent field, and pulled full collective to cushion the landing, but landed hard. The helicopter's drive train consisted of a V-belt sheave bolted directly to the Lycoming reciprocating engine's crankshaft. Four double V-belts transmit power to the upper sheave, which has an overrunning clutch in its hub. The clutch shaft transmits power forward into the main rotor gearbox and mast assembly. According to the operator, the planned route was 7-8 miles, flown at 100 knots and about 900 feet. GPS tracking data indicated that the highest altitude attained was 898 feet mean sea level (msl), which occurred about 2 minutes 30 seconds after takeoff. After that time, the pilot continued on the tour route but began descending with corresponding groundspeed increase. The helicopter was not equipped with an engine monitor. Postaccident examination of the engine compartment revealed the V-belts were coated with oil. The oil sump was drained and found to contain about 4.5 quarts of oil (minimum oil capacity for takeoff is 7 quarts). Further examination of the engine revealed the No. 5 cylinder pushrod (Lycoming part number 15F19957-35) and shroud was fractured in 2 pieces. The engine was removed and sent to a repair station where it was disassembled under the oversight of a Federal Aviation Administration (FAA) airworthiness inspector. Examination of the helicopter revealed damage to the skin of the tailboom. During engine disassembly, valve train components from the No. 5 cylinder and some of the valve train components from the No. 4 cylinder (for comparison) were retained and submitted to the NTSB Materials Laboratory for examination. The governor was also retained for operational testing at the manufacturer's facility with FAA oversight, which revealed the unit passed all required service limits tests. According to the NTSB Materials Laboratory Factual Report, examination of the No. 5 cylinder exhaust valve revealed no evidence of galling on the stem, and no change in surface roughness. Curved impact marks were observed on the face of the valve tip; the shapes of the impact marks were consistent with multiple impacts with the edge of the displaced rotator cap. The valve contact pad on the number 5 exhaust rocker arm exhibited an area of pitting consistent with fretting contact damage. Examination of the No. 5 cylinder exhaust pushrod which was bent and fractured revealed the pushrod pieces were obliterated by post-fracture contact between the mating fractures. Gouges consistent with contact damage with the edge of the rocker arm seat and with the edge of the cylinder flange were observed on the side of the pushrod at the rocker arm end. The contact damage closest to the end of the pushrod was located in line with the inner radius of the bend. The wear pattern at the socket end of the pushrod was angled relative to the longitudinal axis of the pushrod, and was consistent with the pushrod axis angled relative to the socket axis, and the orientation of the angle was consistent with the orientation of the bend in the pushrod. The No. 5 cylinder pushrod housing was fractured near the middle of its length; the fracture surfaces were rough consistent with fracture due to overstress loads. Rub marks consistent with contact with the pushrod were observed on the interior of the pushrod housing. The inboard end of the pushrod housing where it was inserted in the crankcase exhibited areas of impact damage with missing material consistent with contact with the edge of the tappet socket. Corresponding contact marks and material transfer were observed on the edge of the socket. Examination of the valve train components from the No. 4 cylinder, and the springs, spring seats, tappet sockets, tappet bodies, and tappet plunger assemblies associated with both cylinders revealed no evidence of abnormal signatures. A review of the engine logbook revealed the engine was last overhauled on June 21, 2016, and installed in the accident helicopter on January 15, 2017. The engine had accrued 358.2 hours since major overhaul at the time of the accident. The maintenance records reflect that the oil and oil filter were consistently changed every 50 hours or less in accordance with Lycoming Service Bulletin (SB) 480F (multiple logbook entries referenced SB 480E). Lycoming SB No. 388C, which is a repetitive procedure every 300 hours or earlier to determine exhaust valve and guide condition, was last accomplished at 298.3 hours since overhaul. The company Director of Maintenance reported that prior to the accident, they were experiencing 3 to 4 stuck exhaust valves a year among their fleet, adding that none of them resulted in a fractured exhaust valve pushrod or pushrod housing. As a result of the accident, the operator decreased the repetitive inspection interval dictated by SB No. 388C from 300 to 200 hours, and increased the minimum exhaust valve clearance from 0.015 to 0.017 inch. Since incorporating the changes they have operated 60,711 flights, totaling 7,833 flight hours, flying 140,775 passengers, and have not experienced any stuck exhaust valves.
A loss of available power to the main rotor due to a fractured exhaust pushrod and housing, which allowed engine oil to coat the V-belts. Contributing to the accident was the pilot's decision to continue the tour and his failure to maintain adequate rotor rpm during the landing, which resulted in a hard landing.
Source: NTSB Aviation Accident Database
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