Introduction
On October 6, 2021, at approximately 1430 central daylight time, a Bell 206B3 helicopter, registration N373SP, was involved in an accident near Gonzales, Louisiana. The aircraft sustained substantial damage, and the student pilot on board reported minor injuries. The flight was conducted as a public aircraft operation under the Louisiana State Police Air Support Unit.
Flight Details
The student pilot was conducting a short cross-country flight from Baton Rouge, Louisiana, to Louisiana Regional Airport (REG) in Gonzales. About 10 miles from the destination, he obtained meteorological data and selected runway 35 based on wind conditions. Entering the traffic pattern, he completed before-landing checks and observed no anomalies. On the downwind leg, he reduced power and slowed to about 60 knots. After turning final approach, he maintained 400 feet above ground level (AGL) and began a descent, applying a small amount of power to sustain the desired approach angle.
Loss of Control
At approximately 40 knots and 175 feet AGL, the helicopter began to yaw to the right. The student pilot applied left pedal input, but the yaw continued. He noted that the trim indicator showed the helicopter in trim, yet left pedal was still required. Shortly thereafter, the helicopter yawed aggressively to the right. The student pilot applied forward cyclic, causing the helicopter to roll left while continuing a rapid right rotation. Unable to regain control with cyclic inputs, he reduced the throttle to idle. The helicopter settled, and he applied collective to cushion the landing. The helicopter made a hard landing in a flat grass field about 200 feet short of the approach end of runway 35, coming to rest partially upright. The student pilot performed an emergency shutdown and egressed without assistance.
Aftermath
After the accident, the student pilot reported to a responding law enforcement officer that the helicopter had experienced a loss of tail rotor effectiveness (LTE) during the approach. A postaccident examination of the airframe and engine revealed no preimpact mechanical malfunctions or failures that would have precluded normal operation. Due to extensive impact damage, pre-accident tail rotor rigging settings could not be determined. The helicopter was equipped with standard Bell-manufactured tail rotor blades. Maintenance records showed no uncorrected mechanical discrepancies. At the time of the accident, the student pilot had accumulated 42 total flight hours in helicopters, all in the accident make and model. The helicopter weighed 2,661 pounds, 593 pounds below its certified maximum gross weight, and the estimated density altitude was 1,948 feet.
Additional Information
Weather data from REG indicated wind from 260° at 3 knots 35 minutes before the accident, 030° at 4 knots 15 minutes before, and 330° at 5 knots 5 minutes after. The Federal Aviation Administration (FAA) Advisory Circular 90-95, "Unanticipated Right Yaw in Helicopters," describes LTE as a low-speed aerodynamic characteristic that can cause an uncommanded rapid yaw rate. It identifies four relative wind azimuth regions that may contribute to LTE: weathercock stability (120°–240°), tail rotor vortex ring state (210°–330°), main rotor disc vortex interference (285°–315°), and loss of translational lift (all azimuths). The FAA Helicopter Flying Handbook notes that some helicopter types are more susceptible to LTE due to certification thrust margins. Bell has published Operations Safety Notice 206-83-10 and Information Letter 206-84-41 discussing LTE for the Bell 206B3, though the aircraft's Transport Canada-approved rotorcraft flight manual does not contain this information.