Robinson R44 N141TM

Summary

On 17 June 2016 at about 16:45 local time, a Robinson R44 registered N141TM, operated by Ryan Rotors Inc, was involved in an accident near Chatham, Massachusetts, United States. 2 people were on board and 2 were seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

17 June 2016 at 16:45

Classification

Accident

Location

Chatham, Massachusetts, United States

Coordinates

41.7139, -69.9828

Aircraft

Robinson R44

Registration

N141TM

Category

Helicopter

Year built

2002

Engines

1

Operator

Ryan Rotors Inc

Operating rule

Part 91: General Aviation

Purpose of flight

Aerial Observation

Phase of flight

Not recorded

Route

Plymouth → Plymouth

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ERA16LA216

2 people were seriously injured.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.