On July 29, 1984, a Bell 47-G2 (registration N59H) was involved in an aviation accident near Jeffersonville, OH. Investigators recorded the probable cause as: The pilot's loss of main rotor rotation due to excessive collective pitch during takeoff with a heavy load, which led to the aircraft settling and striking a fence. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter loaded with chemicals settled during takeoff. The pilot chose to fly over a fence, but loss of main rotor control caused the tail boom to strike the ground.
What happened
The aircraft began to settle with power during the takeoff phase while carrying a load of chemicals. The pilot faced a decision regarding an obstacle ahead and elected to fly over a fence rather than through it. However, pulling the collective resulted in a loss of main rotor rotation, causing the aircraft to stop flying. During an attempt to flare, the tail boom struck the ground. The impact caused the main blades to flex and sever the tail structure.
The investigation
The mechanical analysis focused on the sequence of events leading to the structural failure. Examination confirmed that the loss of main rotor rotation occurred immediately after the pilot applied collective pitch during the low-speed flight phase. This control input led directly to the loss of lift and the subsequent impact with the ground obstacle.
Findings
Contributing factors included the heavy load configuration and the pilot's decision-making process regarding the fence clearance. The primary causal factor was loss of main rotor rotation due to excessive collective pitch application at low airspeed, which resulted in a hard landing and structural failure of the tail boom.
Probable cause
The pilot's loss of main rotor rotation due to excessive collective pitch during takeoff with a heavy load, which led to the aircraft settling and striking a fence.