Incident Overview
A helicopter on a return flight to a hospital helipad experienced an in-flight mechanical issue during its approach. The crew, consisting of a pilot and two medical crewmembers, heard an external noise. The medical crewmembers reported feeling a slight "shudder" in the aircraft, which they attributed to wind conditions. The pilot also heard the noise but noted no effect on the controls or flight characteristics, allowing the landing to proceed without further incident.
Post-Flight Discovery
After engine shutdown, the oncoming pilot noticed that the helicopter's tail rotor drive shaft cover was missing. A search of the area along the approach path located the missing cover. An examination of the helicopter revealed substantial damage to the tail rotor drive shaft.
Maintenance Background
The day prior to the incident, scheduled maintenance had been performed on the helicopter's tail rotor pitch change mechanism. This procedure required removal of the drive shaft cover. The cover was subsequently reinstalled, and no problems were detected during the following pre-flight inspection.
Likely Cause
It is likely that the cover fasteners were not properly secured after the cover was reinstalled.