Accident Overview
During a medical evacuation flight, an uncontained power turbine burst occurred in the #1 engine of a helicopter. Debris from the #1 engine disabled the #2 engine and severed the tail rotor drive shaft. The #2 engine fire light illuminated, prompting the pilot to discharge the #2 engine fire extinguisher.
Emergency Landing
The pilot performed an autorotative landing. As the helicopter descended, the pilot increased collective pitch to clear trees. The helicopter rolled onto its side at touchdown.
Injuries and Damage
The pilot, one nurse, and the patient were uninjured. Two nurses received minor injuries.
Examination Findings
An examination revealed that the #2 and #3 bearings in the #1 engine had overheated and failed due to a lack of lubrication. Oil passages and jets to the bearings were found clogged with heavy carbon deposits. The engine combustor housing had been changed approximately 13 flight hours before the accident due to a clogged vent strut. After draining the oil, the oil system was not flushed, although flushing was not required.
Engine Susceptibility and Corrective Actions
Evidence showed that Lycoming LTS 101-750C-1 engines were susceptible to carbon clogging. The #2 seals tended to erode, allowing excessive hot gases into the #2 and #3 bearings. Following the accident, the Federal Aviation Administration issued Airworthiness Directive AD 86-22-05, requiring increased inspection and maintenance procedures to prevent recurrence.