Incident Overview
A helicopter experienced substantial damage during a test flight when the transmission cowling detached and impacted the main rotor blade and tail boom. The incident occurred as the helicopter was setting down after being signaled to land.
Preceding Events
According to the pilot, the helicopter had recently undergone maintenance and was preparing for a second test flight. The first test flight had taken place approximately 15 minutes prior to the accident but was cut short due to an inoperative horizontal situation indicator (HSI). A thorough preflight inspection had been conducted for that first flight.
While technicians repaired the HSI, another maintenance technician opened the transmission cowling. Subsequently, the pilot and two avionics technicians boarded the helicopter from the left side. No additional preflight inspection or walk-around was performed before this second flight.
The Incident
The pilot performed a run-up and lifted the helicopter to a hover. At that point, an individual on the ground noticed that the transmission cowling was open. The lead mechanic then signaled to the pilot to land. As the helicopter set back down, the transmission cowling detached from the aircraft. The detached cowling struck a main rotor blade and the tail boom, resulting in substantial damage.
Outcome
The helicopter sustained substantial damage from the collision with the cowling. No further details regarding injuries or other outcomes were provided in the source.
Maintenance and Inspection Issues
The sequence of events highlights that the transmission cowling was opened during repairs to the HSI, and the helicopter was flown without securing it or performing a new preflight inspection. The pilot and technicians boarded from the left side, which may have obstructed a view of the open cowling on the opposite side.