Accident Overview
On December 28, 2023, at approximately 1340 eastern standard time, a Bell 206L-1 helicopter, registration N571CJ, sustained substantial damage during an accident near Walland, Tennessee. The helicopter was operated by Whirl'd Helicopters, Inc., doing business as Scenic Helicopter Tours, as a Title 14 Code of Federal Regulations Part 91 revenue sightseeing flight. The pilot and five passengers were not injured.
The flight departed from Eagles Landing Heliport (03TN) in Sevierville, Tennessee, around 1300 for a local tour. About 35 minutes into the flight, the pilot observed an engine chip light on the instrument panel. The pilot immediately began maneuvering toward a landing area. Within seconds, he heard an abnormal noise from the engine and saw the engine oil temperature and pressure indications decrease to zero. The pilot entered an autorotation and continued maneuvering. About 3 to 5 seconds later, the engine stopped producing power. During the autorotation landing to a field, the helicopter touched down hard, skidded forward several feet, and came to a stop. The main rotor blades contacted one of the vertical stabilizers, nearly severing the tailboom.
Flight and Engine Details
The engine was a Rolls-Royce 250-C28B with 13,378.7 hours time since new (TSN). It was last repaired on July 27, 2021. The gearbox assembly was installed on July 14, 2021, and the compressor assembly on July 27, 2021, at an engine TSN of 12,823.3 hours. The turbine assembly was installed on July 24, 2019, at an engine TSN of 11,980.9 hours.
Postaccident Examination
A field examination revealed that all 4th stage turbine blades were intact, but most blade shrouds were worn away. Manual rotation of the N1 rotor spool resulted in rotation of the N2 rotor spool, indicating a mechanical lock between shafts. The upper chip detector showed a coating of black paste and metallic debris; the lower chip detector was clean. Engine oil tank lines were secure with no leakage. The supply line from the oil tank to the engine contained residual oil, the return line was void of oil, and the engine oil tank contained less than half a tank. About 16 ounces of oil was drained from the accessory gear box.
Engine disassembly showed the compressor module intact and undamaged, and the compressor impeller turned freely. The spur adapter gearshaft (SAG) was intact, and the turbine-to-compressor coupling spline was intact. The aft SAG O-ring was disintegrated into coarse black paste, and no O-ring was found in the forward SAG O-ring groove. The accessory gearbox internal components and oil pumps were undamaged and well lubricated.
The 4th stage turbine wheel was intact but showed rotational smearing on the curvic coupling with the 3rd stage turbine wheel. Most blade shrouds were rotationally abraded, consistent with contact against wheel tracks. The 4th stage turbine nozzle had rotational scoring on wheel tracks. The power turbine bearing support was intact, but the 3rd and 1st stage turbine wheels could not be withdrawn due to fractured and deformed turbine-to-compressor coupling and power turbine inner shaft, locking the 3rd stage wheel. The 3rd stage wheel was intact with rotational smearing on its curvic coupling; all blades were intact. The combustor case, liner, and fuel nozzle were undamaged.
The No. 8 bearing sump cavity was dry and coated with black residue. The No. 8 bearing spanner nut was untorqued and backed out to the last thread. It exhibited one partial crimp and two blended locations. The partial crimp had a pry mark on the inner surface, consistent with removal during last disassembly, and the inner surface was oxidized, indicating a non-contact condition. No evidence of a locking crimp made during the last assembly was found. The No. 8 bearing sump cover showed rotational scoring from contact with the nut. The No. 8 bearing exhibited significant wear and thermal damage to balls and inner ring, with loss of the forward shoulder of the inner raceway ring. Rub damage on the power turbine support and 2nd stage turbine wheel was consistent with loss of axial and radial retention of the gas producer rotor during operation.