Incident Overview
On May 23, 2013, at approximately 2100 central daylight time, a Bell 206B helicopter (registration N297CA) performed an autorotation to a forced landing at the Spirit of St. Louis Airport (KSUS) in St. Louis, Missouri. The flight instructor and a commercial-rated pilot were not injured, and the helicopter was substantially damaged. The helicopter was registered to GM Leasing Co., LLC and operated by Air-Evac Lifeteam, O'Fallon, Missouri, under 14 CFR Part 91 as a training flight. Night visual meteorological conditions prevailed, and the flight operated on a company flight plan.
Sequence of Events
According to the flight instructor, he was demonstrating a normal takeoff. As the helicopter accelerated to about 50 knots and reached an altitude of 20 feet, a loud bang was heard. The helicopter yawed left, and the instructor elected to perform an autorotation landing with forward airspeed onto a taxiway.
Aircraft and Engine Examination
An initial visual inspection of the airframe revealed no observable damage. However, inspection of the Rolls-Royce 250-C20B engine disclosed a case breach on the axial compressor. Further examination of the airframe showed substantial damage to the aft fuselage and main rotor system. Engine maintenance records indicated the engine had 15,179.6 hours time since new (TSN) and 4,948 cycles TSN. The compressor had 13,874 hours TSN, and the compressor rotor stage 1-6 wheels had 1,185.3 hours TSN and were Parts Manufacturer Approval (PMA) replacement parts.
Engine Component Findings
Examination revealed several areas where the compressor case had been breached by fragments exiting the engine. The stage 1 compressor blades were in place and in good condition. Stage 2 blades were present but exhibited varying degrees of trailing edge damage. All stage 3 through 6 blades had separated at the blade root. The 3, 4, and 6 compressor stator vanes were completely separated and ingested; stage 2 and 5 vanes were present but bent or torn in the direction of rotation.
The compressor impeller was intact but had leading edge damage 360 degrees around the disk. Several impeller blades exhibited blade tip bending consistent with debris ingestion.
NTSB Materials Lab Analysis
The axial compressor rotor and stator were sent to the National Transportation Safety Board (NTSB) materials lab in Washington, D.C. Examination of the 3rd stage wheel found a blade root with about 54% progressive cracking area, consistent with fatigue. The examination also found indications of fatigue on stage 3 through 6 blades.
Damage Assessment
The helicopter sustained substantial damage, including the aft fuselage and main rotor system, as well as engine case breaches and internal compressor damage.