Accident Overview
On August 2, 2018, at about 0920 mountain daylight time, a Bell 47G 3B helicopter, registration N347BH, sustained substantial damage during a forced landing near Custer, South Dakota. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The pilot and passenger were not injured; the flight instructor received minor injuries.
Pre-Accident Events
The commercial-rated pilot and the flight instructor had completed several training flights in the accident helicopter prior to the accident flight to familiarize the pilot with Bell 47 helicopters. On the morning of the accident, the pilot conducted hover practice and three circuits in the traffic pattern at Crazy Horse Heliport (0SD9) in Custer. The flight instructor did not intervene during the pattern work, and the dual flight controls were subsequently removed to allow for an additional occupant and to simulate a heavier load that the pilot would encounter during future tour flight operations.
Accident Sequence
After picking up a passenger, the pilot and flight instructor practiced hovering and a low-rotor-rpm recovery. The helicopter then departed 0SD9 and followed a left traffic pattern. During the approach to land, at about 100 feet above ground level, the pilot noted that the rotor rpm dropped below the normal operating range. She increased throttle but was unable to recover the rotor rpm within the normal range. The flight instructor stated that the helicopter lost altitude quickly and there was no time to recover. He explained that the turbocharger on the engine had “some lag, the rotor rpm does not come back up with only opening the throttle but lowering the collective at that time was not an option due to the low altitude.”
Forced Landing and Damage
The helicopter continued descending toward the ground as oncoming traffic approached on a nearby road. The pilot executed a forced landing in a grassy area on the side of a highway. During the landing, the right skid caught on uneven ground, causing the helicopter to roll over to the right on the sloping terrain. This rollover substantially damaged the tail section and tail rotor.
Engine Performance
The flight instructor reported that the engine did not “shutter,” “kick,” or demonstrate any other anomaly before or during the event, and that the engine “performed well.” He also noted that the engine had not exhibited issues on any of the previous flights.