What happened
On April 26, 2016, at approximately 1500 EDT, a MBB BK 117 C-2 helicopter, registration N145HN, was performing an on-demand air medical flight from Grafton City Hospital Heliport (22WV) in Grafton, West Virginia, to West Penn Hospital Heliport (PN80) in Pittsburgh, Pennsylvania. The flight was conducted under visual meteorological conditions with a wind of 250 degrees at 16 knots and 10 miles of visibility.
During the cruise phase of the flight, the left vertical fin cowling partially separated from the aircraft. This separation caused the cowling to come into contact with a tailrotor blade. The pilot reported that the flight was uneventful until the discovery of the damage after landing. There were no injuries to the pilot, the three crewmembers, or the patient being transported.
The investigation
An inspection by the Federal Aviation Administration (FAA) found that while the Dzus fasteners on the right vertical fin cowling were secure, 8 of the 11 fasteners on the left vertical fin cowling were unlocked. This condition was consistent with the fasteners not being properly secured by maintenance personnel following maintenance work performed on the helicopter earlier that morning.
Representatives from the helicopter manufacturer examined the tailrotor blade and determined it had sustained substantial damage due to the impact with the cowling.