Accident Overview
On September 28, 2019, about 1930 eastern daylight time, an Enstrom F-28F helicopter, registration N380SH, was substantially damaged when it impacted terrain and vehicles during an approach to a helipad at the Bloomsburg Fair in Bloomsburg, Pennsylvania. The commercial pilot sustained serious injuries, and the two passengers sustained minor injuries. The helicopter was operated by J&J Shop HeliAir LLC under Title 14 Code of Federal Regulations Part 91 as a local sightseeing flight.
Pilot Report
The pilot reported that the accident flight was the last helicopter ride the operator planned to fly, as it was the 10th and final day of fairgrounds flying. He completed a routine 3-minute flight around the fairgrounds and approached the paved helipad as he normally did. During the final approach, the helicopter "just yawed right," and he applied left pedal but said the action "did not stop the yaw." He could not recall the power settings or the height above ground when the loss of yaw control occurred, nor did he remember hearing or seeing an alarm. He described it as "just a standard approach" with "nothing unusual about it." The pilot reported no mechanical malfunctions or failures.
Video Evidence
Surveillance videos captured the final 19 seconds of the flight. The helicopter approached the helipad over several vehicles in the fairgrounds parking lot. The approach was shallow and at about the speed of a hover-taxi. The helicopter then momentarily climbed as its forward momentum stopped, and a right yaw (spin) began. The helicopter subsequently descended and completed two and a half rotations around the main rotor mast before impacting vehicles and terrain. The helicopter appeared about 20–25 ft above the terrain when the right yaw began. A windsock visible in the surveillance video indicated calm wind.
Post-Accident Examination
A post-accident examination and photographs from a Federal Aviation Administration inspector revealed that the helicopter came to rest on its left side. The fuselage, tail boom, main rotor, and tail rotor sustained substantial damage. The passenger doors were not installed. Continuity for the cyclic and collective controls was confirmed. Examination of the engine showed no evidence of catastrophic internal failures, and no anomalies were observed with the spark plugs or magnetos.
Additional Information
Weight and balance calculations, based on estimations of the pilot and passenger weights and 16 gallons of fuel, indicated the helicopter was likely within its center-of-gravity limits and about 220 lbs under its maximum allowable gross weight. The pilot's operating handbook listed the rotor diameter as 32 ft. Based on nearby weather observations, the density altitude at the accident site was about 1,550 ft.
Federal Aviation Administration Advisory Circular (AC) 90-95, titled "Unanticipated Right Yaw in Helicopters," was issued in February 1995. The AC describes loss of tail rotor effectiveness (LTE) as a critical, low-speed aerodynamic flight characteristic that can result in an uncommanded rapid yaw rate, which does not subside on its own and, if uncorrected, could lead to loss of aircraft control. It states that LTE is not related to a maintenance malfunction and may occur in varying degrees in all single main rotor helicopters at airspeeds less than 30 knots. Paragraph 8 of the AC lists factors that can influence the severity of LTE onset, including gross weight and density altitude, low indicated airspeed, and power droop.
The FAA Helicopter Flying Handbook notes that ground effect increases rotor efficiency near the surface, with maximum effect when hovering over smooth hard surfaces. For most helicopters, rotor efficiency is increased by ground effect up to a height of about one rotor diameter above the ground.