Chatham, MA, USA
N141TM
ROBINSON HELICOPTER R44
The commercial pilot reported that, during an aerial photography flight, the helicopter was about 300 ft above a pond when it experienced an engine overspeed, followed by a loss of engine power. The pilot subsequently entered an autorotation to shallow water. Examination of the engine revealed that the No. 2 cylinder head rocker shaft bosses, the No. 2 intake valve upper spring, and the No. 3 intake valve spring seat were fractured, consistent with an engine overspeed. Examination of the airframe revealed that the engine cooling fan shaft had separated. Without the resistance of the fan shaft, the engine oversped, which resulted in sufficient engine damage for the engine to lose total power. The aft face of the fan shaft's lower sheave exhibited caked-on grease, consistent with grease leaking beyond the lower forward clutch actuator bearing seal for a prolonged period of time. Metallurgical examination of the bearing revealed that its rollers were seized, and no grease was recovered, consistent with a lack of lubrication. The helicopter manufacturer's maintenance manual required that the entire airframe be overhauled every 2,200 hours, which would include an overhaul of the engine cooling fan driveshaft lower bearing and seal. Review of maintenance records revealed that, due to a maintenance logbook entry error (time since overhaul) that occurred about 9 years before the accident and was carried forward, the helicopter had been operated about 52 hours beyond the mandatory airframe overhaul time limit. The manual also required that the lower clutch actuator bearings be lubricated every 300 hours or 3 years, whichever occurred first. Although the failed bearing had been lubricated with grease both about 1 year and 2 years preceding the accident, there was no record indicating that the bearing had been lubricated with grease during the preceding 4 years 11 months and 685.1 hours of operation, which likely damaged or degraded the bearing and led to its failure during the accident flight.
On June 17, 2016, about 1245 eastern daylight time, a Robinson R44, N141TM, operated by Ryan Rotors, was substantially damaged during a forced landing to a pond, following a total loss of engine power while maneuvering near Chatham, Massachusetts. The commercial pilot and passenger were seriously injured. The local aerial photography flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed for the flight that originated Plymouth Municipal Airport (PYM), Plymouth, Massachusetts, about 1026.The pilot reported that the passenger hired him so that she could take aerial photographs of real estate. The helicopter was over a saltwater pond, about 300 feet above ground level, approaching homes near the shoreline. At that time, the pilot felt a lateral shudder followed by the clutch light illuminating. The helicopter then began a violent yaw and the low oil pressure light illuminated. The pilot subsequently performed an autorotation to shallow water near the shoreline. Review of data downloaded and plotted from a handheld GPS revealed that the helicopter proceeded along the north shore of Cape Cod after departing PYM, then transitioned to the south shore near Dennis, Massachusetts. The helicopter continued along the south shore and in the Chatham, Massachusetts area, completing many circuits, consistent with aerial photography. The last two data points recorded indicated a GPS altitude of 402 feet and 268 feet, respectively. Examination of the wreckage by a Federal Aviation Administration inspector revealed that the helicopter came to rest on its left side at the edge of a pond. The inspector observed substantial damage to the airframe and also noted that a rocker arm was protruding from the engine crankcase. The wreckage was examined again at a recovery facility. Examination of the engine revealed that the No. 2 and No. 3 cylinders exhibited damage consistent with engine overspeed. Specifically, the No. 2 cylinder head rocker shaft bosses were fractured and the No. 2 intake valve upper spring was fractured. The No. 3 intake valve spring seat was also fractured. Examination of the airframe revealed that the engine cooling fan shaft had separated. Examination of the aft face of lower sheave revealed caked on grease, consistent with grease leaking beyond the lower forward clutch actuator bearing seal over a period of time. Metallurgical examination of the bearing revealed that its rollers were seized and no grease was recovered, consistent with a lack of lubrication (For more information, see Material Laboratory Factual Report in the NTSB Public Docket). The seal and bearing housing were severely damaged during the accident, which precluded determination of the exact point on the seal that was compromised. Review of maintenance records that the helicopter's most recent 100-hour inspection was completed on April 23, 2016. At that time, the helicopter's total time airframe (TTAF) was noted as 2,192.4 hours and time since the airframe was overhauled (TSOH) was noted as 1,637.4 hours. Review of the helicopter's hour meter after the accident revealed that it had flown an additional 59.5 hours since that inspection, resulting in a TTAF of 2,251.9 and TSOH of 1,696.9 hours. Further review of the aircraft logbook revealed that an extensive repair and annual/100-hour inspection was completed on July 12, 2006, at the manufacturer's facility. Although the engine was overhauled during the repair, the airframe was not. An employee of the manufacturer correctly noted repair (verses overhaul) in the airframe logbook entry, but incorrectly noted the TSOH as 4.2 hours rather than 559.2 hours. The erroneous TSOH recording carried forward throughout the aircraft logbook. At the time of the accident, the TTAF and TSOH for the airframe were both 2,251.9 hours. The helicopter manufacturer required the airframe to be overhauled by the manufacturer every 2,200 hours, during which, the engine cooling fan driveshaft lower bearing and seal would have been overhauled. Review of Robinson Helicopter Company Service Bulletin (SB)-42 revealed a requirement to service the lower clutch actuator bearings with grease every 300 hours or annually, whichever occurred first, to prevent failure due to lack of lubrication. The SB was superseded by an addition to the maintenance manual that required a similar procedure of every 300 hours or every 3 years, whichever occurred first. Review of the maintenance records revealed that the lower clutch actuator bearings were most recently serviced on December 17, 2015, at a TTAF of 2,095.1 hours. They were previously serviced on September 17, 2014 at a TTAF of 1,885.4 hours and May 11, 2011 at a TTAF of 1244.3. Prior to that, the last recorded servicing was on June 13, 2006 at a TTAF 559.2 hours, resulting in no recorded servicing during a period of 4 years 11 months and 685.1 hours of operation. Further, the maintenance manual also contained instructions to check the condition of the lower clutch actuator bearing seals at every 100-hour or annual inspection. The was no record of the failed seal having ever been replaced.
The inadequate maintenance of the lower forward clutch actuator bearing for a prolonged period of time, which resulted in a bearing failure. Contributing to the accident was an erroneous maintenance entry, which resulted in the helicopter being operated beyond its mandatory airframe overhaul time.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
