CEN20FA035

A total loss of engine power due to the failure of the engine’s Nos. 3 and 4 bearings and the power turbine pinion gear, and subsequent loss of main rotor rpm, which resulted in a loss of control and impact with the water.

The helicopter was flying over the Gulf of Mexico between two oil platforms. Flight track data showed the helicopter in cruise flight at 700 ft mean sea level (msl) before it gradually descended to 375 ft msl. Just before the data ended, the helicopter entered a left turn, descended to 150 ft msl, and slowed from about 115 knots (kts) groundspeed to about 75 kts groundspeed. The helicopter impacted the water and sank to the sea floor. The main wreckage was eventually located on the sea floor about 350 ft southwest of the last recorded flight track point. Examination of the engine revealed that the power turbine pinion gear teeth were significantly worn and smeared, which ultimately resulted in the engine’s inability to provide power to the rotor system. While the majority of the No. 3 bearing was not recovered, the significant thermal damage and loss of material of the power turbine pinion gear shoulder, to which the No. 3 bearing inner race was installed, indicated that the bearing likely failed first, but the cause of the No. 3 bearing failure could not be determined because the bearing was not recovered. The failure of the No. 3 bearing could result in misalignment of the gear mesh between the power turbine pinion gear and the torquemeter gear, which likely caused the pinion gear teeth to rapidly degrade and/or fracture. The initial failure of the No. 3 bearing would have resulted in the failure of the No. 4 bearing and the power turbine pinion gear. The reasons why damage to the Nos. 3 and 4 bearings and the power turbine pinion gear did not result in an engine chip light or oil filter contamination, leading to a filter bypass indication, could not be determined based on the available evidence. The blockages observed in the oil delivery tube and oil nozzle were consistent with corrosion, likely due to postaccident saltwater immersion; therefore, whether there were any preexisting anomalies of the oil delivery tube jets and/or the oil nozzle, such as oil coking, could not be determined. However, the remainder of the recovered engine bearings and gears did not show evidence of damage associated with a widespread lubrication issue. Analysis of the caution and warning panel bulb filaments showed that several annunciator lights were illuminated at the time of impact, consistent with the effects of a loss of engine power due to a failure of the power turbine pinion gear. The main rotor rpm warning light would have illuminated within a second of the loss of engine power as main rotor speed (Nr) decreased, and the hydraulic system and transmission oil pressure annunciator lights would have illuminated once Nr decreased to critical levels. The data downloaded from the helicopter’s engine control unit was also consistent with a loss of engine power and subsequent loss of Nr. While collective pitch was reduced for a few seconds after the loss of engine power, collective pitch was subsequently increased, which led to a quicker decay of Nr. The substantial decrease in Nr would have affected controllability of the helicopter and ultimately resulted in a loss of control. The pilot’s cyclic and pedal inputs, as well as the helicopter’s attitude and airspeed, at the time of the loss of engine power were not known. Therefore, it could not be determined if the pilot successfully entered autorotation or the reasons why the pilot increased collective control about 3 seconds after the loss of engine power. There was no evidence that the emergency flotation system was deployed. While flight track data for the accident flight was available, the last few data points were discontinuous and could not be reliably matched with the recorded engine data; therefore, it could not be determined if the pilot was in a position to deploy the emergency flotation system following the loss of power.

The pilot initially departed Grand Isle, Louisiana, about 0655 on the morning of the accident. He accumulated over 2 hours of flight time and was on the eighth leg of the day when the accident occurred. At the time of the accident, the helicopter had an aircraft total time (ATT) of 8,500.8 hours and an engine total time (ETT) of 7,584.7 hours. The engine was installed on the accident helicopter on November 16, 2016, at an ATT of 6,811.6 hours and ETT of 6,264.6 hours. A 600-hour/12-month inspection and an engine oil change were last performed on May 12, 2019, at an ATT of 7,786.3 hours (ETT of 6,870.2 hours) as well as on October 21, 2019, at an ATT of 8,382.1 hours (ETT of 7,466.0 hours). According to the operator’s director of maintenance, during a typical engine oil change, the combined engine filter assembly (CEFA) oil filter, which filters engine scavenge oil, is inspected for contamination and reinstalled if none is found. A review of the engine and aircraft maintenance records from April 2018 until December 2019 found no entries regarding engine chip indications. During that timeframe, there were two instances of the CEFA oil filter bypass indicator extending, the first on April 24, 2018, at an ATT of 7,180.7 hours (ETT of 6,264.6 hours) and the second on September 25, 2019, at an ATT of 8,286.6 hours (ETT of 7,370.5 hours), neither of which found contamination of the CEFA oil filter. According to the director of maintenance, the CEFA oil filter bypass indicator extending is not a common occurrence but can happen in colder ambient temperatures. The maintenance records showed that the accident engine was last overhauled in September 2016 at an ETT of 5,894.1 hours. The last overhaul included completion of the 2,000-hour nonintrusive gearbox inspection, a visual inspection primarily aimed at the power turbine pinion and torquemeter gear mesh. No anomalous findings were reported. The main fuselage was fractured, folded, and twisted in multiple locations, but remained connected via wiring and netting from the shrimp trawler. The forward portion of the tail boom remained connected to the intermediate fuselage but was fractured at the tail boom tube structure. The remainder of the tail boom, including the vertical and horizontal stabilizers, was not recovered. The main rotor gearbox remained attached to the transmission deck. The gearbox housing exhibited extensive corrosion due to saltwater immersion. The main rotor gearbox chip detectors were removed and exhibited extensive corrosion, but no metallic chips were present. The emergency flotation system was installed under the provisions of Supplemental Type Certificate SR01450LA. All floats were found outside their covers but did not show evidence of inflation and exhibited a vacuum-deflated appearance. The engine was separated from the airframe but remained partially attached via the wiring harness. The majority of the accessory gearbox housing was consumed by corrosion due to saltwater immersion, and the compressor section was partially separated from the combustion and turbine sections. The airframe-mounted fuel filter remained attached to the airframe and was removed from its mount and disassembled. The fuel filter bowl contained about 0.25 ounces of liquid with a color and odor similar to that of Jet A fuel and the fuel filter was clear of contaminants. The throttle lever was present and indicated about 15 degrees, which corresponded to below idle and beyond the throttle lock-out. The CEFA was impact-separated from the wreckage. The CEFA’s oil filter bypass indicator was not extended, which is the position for when the filter is not in bypass mode. Residual oil and fuel, along with salt water, were present in the CEFA, including the filter bowls. The fuel filter element was removed, and no debris was observed. The scavenge oil filter element was removed and metallic debris was found on the filter element and its filter bowl. Several gears and engine accessories from the accessory gearbox were recovered separated from the engine assembly. The power turbine pinion gear, part of the power turbine-to-pinion (N2) gear train, was found loose in the accessory gearbox and exhibited severe wear and smearing damage on its gear teeth and bearing shoulders. Figure 2 shows a comparison of the accident power turbine pinion gear (left) to an exemplar power turbine pinion gear (right). Figure 2 – Accident power turbine pinion gear (left) and an exemplar power turbine pinion gear (right). The No. 4 roller bearing, normally installed on the aft end of the power turbine pinion gear, was severely worn and its roller elements were found loose in the gearbox cavity, along with the pinion gear. Nine of the twelve roller elements from the No. 4 bearing were recovered. The No. 3 roller bearing outer ring was present and exhibited severe wear. The inner race, roller elements, and bearing cage for the No. 3 bearing were not recovered. The engine was relocated to a specialized engine shop and disassembled. The oil nozzle for the Nos. 4 and 5 bearings remained attached to the gearbox and were corroded but did not exhibit other damage. The No. 5 bearing did not exhibit anomalous wear. Corrosion and mud were observed throughout the accessory gearbox, and additional roller elements from the Nos. 3 or 4 bearings were not found in the remnant mud or within the gearbox. The oil delivery tube for the Nos. 3 and 4 bearings, also known as the “piccolo tube,” exhibited severe corrosion. The following engine components were identified for additional testing and analysis: the No. 4 bearing; the piccolo tube oil nozzle; the oil nozzle for the Nos. 4 and 5 bearings; the housing for the Nos. 3 and 4 bearing; the power takeoff gear; the power turbine pinion gear; the scavenge oil filter and its filter bowl; the pressurized oil filter; the N2 shaft; the No. 2.5 bearing and its support; and an oil sample from the CEFA oil filter. On December 7, 2019, at 0918 central standard time, a Bell 407 helicopter, N79LP, was destroyed when it was involved in an accident in the Gulf of Mexico, about 25 nautical miles southeast of Grand Isle, Louisiana. The pilot and passenger were fatally injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 business flight.   In a statement provided by the operator, the helicopter had departed oil platform SP77A about 0834 and was en route to platform WD73, located about 17 nautical miles northwest. The pilot was to conduct pollution control inspections while en route to the destination platform. At 0853, the pilot landed at platform WD109 for additional fuel, but discovered that the fuel nozzle was broken and was unable to refuel. At 0910, the helicopter departed platform WD109 with 1 hour and 20 minutes of fuel reported, 2 persons onboard, and estimated time en route of 20 minutes. The operator tracked the helicopter via Sky Connect Tracker Systems. Recorded ADS-B data revealed that the helicopter’s flight track began at 0912:50 about 1.5 miles west-northwest of platform WD109 at 700 ft mean sea level (msl) and 115 knots groundspeed. The helicopter continued northwest for about 10.5 miles and gradually descended to 375 ft msl. At 0918:10, the helicopter’s heading was 292° at a groundspeed of 114 knots and altitude of 375 ft msl. The final recorded point, at 0918:18, showed that the helicopter made a left course deviation to 270°, descended to 150 ft msl, and slowed to 72 knots. Figure 1 shows the platforms, recorded ADS-B flight path, and initial main wreckage location. Figure 1 – Main wreckage location, flight track and platforms. At 0915, the pilot contacted WD73 personnel and reported that he was 10 minutes from the platform. At 1011, when the helicopter had not landed at WD73, platform personnel reported it overdue. An alert notice (ALNOT) was issued at 1121. The United States Coast Guard recovered several smal