Accident Details
On June 17, 2016, at approximately 1245 eastern daylight time, a Robinson R44 helicopter, registration N141TM, operated by Ryan Rotors, was substantially damaged during a forced landing in a pond. The aircraft experienced a total loss of engine power while maneuvering near Chatham, Massachusetts. The commercial pilot and one passenger sustained serious injuries. The flight was conducted under 14 Code of Federal Regulations Part 91 for local aerial photography. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Plymouth Municipal Airport (PYM), Plymouth, Massachusetts, at about 1026.
The pilot reported that the passenger had hired him to take aerial photographs of real estate. While over a saltwater pond at an altitude of about 300 feet above ground level, approaching homes near the shoreline, the pilot felt a lateral shudder followed by the illumination of the clutch light. The helicopter then experienced a violent yaw, and the low oil pressure light illuminated. The pilot performed an autorotation to shallow water near the shoreline.
GPS Data and Flight Path
A handheld GPS device recorded the helicopter's flight path. After departing PYM, the helicopter proceeded along the north shore of Cape Cod, then transitioned to the south shore near Dennis, Massachusetts. It continued along the south shore and in the Chatham area, completing many circuits consistent with aerial photography. The last two data points indicated GPS altitudes of 402 feet and 268 feet, respectively.
Wreckage and Engine Examination
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. Substantial damage to the airframe was observed, and a rocker arm was found protruding from the engine crankcase. Further examination at a recovery facility 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, the No. 2 intake valve upper spring was fractured, and the No. 3 intake valve spring seat was fractured.
Examination of the airframe revealed that the engine cooling fan shaft had separated. The aft face of the lower sheave showed caked-on grease, consistent with grease leaking beyond the lower forward clutch actuator bearing seal over time. Metallurgical examination of the bearing showed its rollers were seized, and no grease was recovered, consistent with a lack of lubrication. The seal and bearing housing were severely damaged during the accident, preventing determination of the exact point of seal compromise.
Maintenance History
Review of maintenance records indicated that the helicopter's most recent 100-hour inspection was completed on April 23, 2016, at a total time airframe (TTAF) of 2,192.4 hours and time since overhaul (TSOH) of 1,637.4 hours. After the accident, the hour meter showed an additional 59.5 hours, resulting in a TTAF of 2,251.9 and TSOH of 1,696.9 hours. Further review revealed an extensive repair and annual/100-hour inspection completed on July 12, 2006, at the manufacturer's facility. Although the engine was overhauled during that repair, the airframe was not. An employee incorrectly noted the TSOH as 4.2 hours instead of 559.2 hours, and this erroneous entry carried forward. At the time of the accident, the TTAF and TSOH for the airframe were both 2,251.9 hours. The manufacturer required airframe overhaul every 2,200 hours, which would have included overhaul of the engine cooling fan driveshaft lower bearing and seal.
Robinson Helicopter Company Service Bulletin (SB)-42 required servicing of the lower clutch actuator bearings with grease every 300 hours or annually, whichever occurred first, to prevent failure due to lack of lubrication. This SB was later superseded by a maintenance manual addition requiring servicing every 300 hours or every 3 years. Records showed the bearings were last serviced on December 17, 2015, at a TTAF of 2,095.1 hours, with prior services on September 17, 2014 (1,885.4 TTAF) and May 11, 2011 (1,244.3 TTAF). Before that, the last recorded servicing was on June 13, 2006 (559.2 TTAF), resulting in no recorded servicing for a period of 4 years 11 months and 685.1 hours of operation. The maintenance manual also required checking the condition of the lower clutch actuator bearing seals at every 100-hour or annual inspection, but there was no record of the failed seal having ever been replaced.