N5842ZMd Helicopters 369FF

On July 24, 2015, about 0945 Atlantic standard time, an MD Helicopters Inc. 369FF, N5842Z, was substantially damaged when it impacted shallow water near Vega Baja, Puerto Rico. The commercial pilot, pilot-rated passenger, and another passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which originated from Luis Munoz Marin International Airport (SJU), San Juan, Puerto Rico and was destined for Antonio (Nery) Juarbe Pol Airport (ABO), Arecibo, Puerto Rico. The work use flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.

The helicopter was operated by the Puerto Rico Electric Power Authority and was assisting with electrical power distribution system construction. The helicopter departed from SJU and proceeded to the work site, cruising at an altitude of 300 feet along the northern coastline of Puerto Rico. About 20 minutes into the flight, the pilot heard a loud "bang" emanate from the area of the engine, followed by a second bang 2 to 3 seconds later. The engine then experienced a total loss of power and the pilot responded by entering an autorotative descent. During the descent, the pilot recalled hearing and observing the "low engine rpm" annunciations. The helicopter subsequently impacted an area of shallow water near a beach. During the landing, the main rotor struck the tail boom, separating it from the fuselage.

Examination of the engine revealed that the power section was not free to rotate, and borescope examination revealed thermal damage to the first stage turbine blades. The engine oil was drained, and examination of the oil and oil filter element revealed slivers and chips of ferrous metal. Detailed examination of the engine revealed that the No. 2 bearing was damaged. The bearing displayed evidence of thermal distress, spalling of the balls and races, and the ball separator was fractured. The oil delivery tube (also referred to as a "piccolo tube") that serviced the bearing with oil was installed and undamaged. Metallurgical examination of the No. 2 bearing showed a thermal distress pattern consistent with a possible reduction in oil flow to the bearing. The bearing's metallurgical composition was consistent with the material types specified in its design. X-ray examination of the bearing's oil delivery tube revealed no evidence of obstruction or restrictions; the inlet screen was absent of debris.

The oil delivery tube installed in the accident engine was subject to a Commercial Engine Bulletin published by the manufacturer (CEB-72-3299), which was effective for all engines built before November 30, 2014. The bulletin stated that the reason for the part replacement was to, "…improve oil delivery to the #2 thrust bearing. This change will decrease the bearing temperature and improve the bearing performance." The bulletin further stated that it should be complied with the next time the engine's gearbox was at an authorized repair/overhaul facility and was disassembled for any reason.