N79LP

HISTORY OF FLIGHTOn 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 small pieces of the helicopter, including a cargo door, a compressed gas cylinder, and seat cushions. The debris was found near another platform about 25 miles west of where the main wreckage was eventually located.

On December 14, 2019, during a side-scan sonar mission near the last ADS-B point, the sonar hooked onto the left skid tube of the helicopter. The sonar boat pulled the skid tube up to the boat and transferred it to the wreckage recovery company. Pieces of helicopter debris were visible on the sonar images, and divers marked the location for a future recovery. The main wreckage location was about 350 ft southwest of the last ADS-B point and was on the sea floor, about 190 ft underwater. Due to adverse weather in the Gulf of Mexico, the recovery was postponed until December 20, 2019.

On December 16, 2019, a shrimp trawler unintentionally caught the helicopter wreckage in its nets and dragged the wreckage about 3 miles. When the wreckage was noticed to be caught in the net, the trawler stopped, and the wreckage eventually broke loose and sank back to the sea floor. The main wreckage was recovered from the Gulf of Mexico on December 20, 2019, and transported to a recovery facility in Louisiana.

PERSONNEL INFORMATIONThe 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.

AIRCRAFT INFORMATIONAt 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.

METEOROLOGICAL INFORMATIONThe weather in the area was reported by the operator as wind from 050° at 10 knots, broken clouds at 1,700 ft, no precipitation, and 5 miles visibility in haze. A platform WD73 worker reported the clouds were 800 to 1,000 ft, and 7 to 10 miles visibility with a gray sky.

AIRPORT INFORMATIONAt 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.

WRECKAGE AND IMPACT INFORMATIONThe 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 f...