Accident Details
Shortly after takeoff, the pilot radioed that he was returning to the airport due to poor visual flight conditions. He was last seen circling the runway. Approximately seven hours later, the wreckage was found about 150 yards north of the runway. The main rotor (M/R) system showed significant damage: the blue M/R blade had separated, and the trailing attachment lugs of both the upper and lower blade root fittings were fractured through the holes. Additionally, the lead-lag damper lug was also fractured.
Metallurgical Examination
Metallurgical examination of the four fractured blade root fittings revealed fatigue progression on all fractures. The fatigue cracks had propagated through the attachment lugs, leading to the eventual separation of the blade.
Maintenance Oversight
Operator maintenance personnel stated that they were not aware of the requirement in Airworthiness Directive (AD) 91-17-04 to remove and inspect the M/R blades at 100-hour intervals. This directive mandates periodic inspections to detect fatigue cracks or other damage that could compromise the integrity of the rotor system.
Investigation Findings
The investigation determined that the fatigue fractures in the blade root fittings were present before the accident. The lack of compliance with the mandatory inspection requirement meant that the fatigue cracks went undetected, ultimately leading to in-flight blade separation.