Accident Overview
On June 4, 2022, about 1201 eastern daylight time, a Bell 407 GXP helicopter (registration N98ZA) was substantially damaged during an accident near Fairfield, New Jersey. The commercial pilot, who was the sole occupant, sustained serious injuries. The helicopter was being operated as a Title 14 Code of Federal Regulations Part 91 positioning flight.
Flight History
The helicopter departed Essex County Airport (CDW), Caldwell, New Jersey, about 1147 for John F. Kennedy International Airport (JFK), Queens, New York. Automatic dependent surveillance-broadcast (ADS-B) data indicated the helicopter was cruising at about 500 ft mean sea level (msl) on a southeasterly track. At approximately 1152, while about 2 miles south of Teterboro International Airport (TEB), the pilot asked, “what is going on here?” About one minute later, the pilot requested a return to CDW. The controller asked if assistance was needed; the pilot declined.
The helicopter turned left toward CDW at about 500 ft msl and 85 knots indicated airspeed. At 1155, the pilot told CDW tower he “may need the runway.” The controller cleared the helicopter to land on runway 28. At 1158, the pilot reported 2 miles out, and the controller cleared the helicopter to land “on the numbers.” The helicopter’s airspeed decreased as it approached.
At about 1200, the helicopter crossed airport property with its nose slightly pitched up and airspeed decreasing below 65 knots. At 250 ft msl with the runway visible, the helicopter began yawing right as airspeed dropped below 35 knots. The right yaw increased as airspeed fell below 30 knots. Near treetop level at 0 knots, the yaw stopped, then the helicopter yawed left and rolled slightly left. It then entered a rapid right yaw, pitched forward, and descended while rotating around the main rotor mast. The helicopter completed several 360° rotations before impacting terrain north of runway 28, causing substantial damage to the fuselage and tailboom.
Airport surveillance video showed the helicopter’s approach, nose pitch-up, deceleration, right yaw, instability, and vertical descent with rotation. About 3 seconds into the vertical descent, right yaw slowed and stopped, then the helicopter rotated left as it contacted the ground. After impact, main rotor blades shed about 50% of their span.
Personnel Information
The pilot held a commercial pilot certificate with ratings for rotorcraft-helicopter and instrument helicopter, as well as a flight instructor certificate with the same ratings. He received 16 hours of initial ground instruction in the Bell 407 (including systems, performance planning, and emergency procedures) and general subjects, plus 5 hours of flight training. He satisfactorily completed a Part 135 airman competency/proficiency check in the Bell 407 on May 16, 2020, demonstrating satisfactory knowledge of emergency procedures for settling with power and tail rotor failure.
Aircraft and Maintenance Information
According to the operator, the tail rotor was installed the day before the accident after replacement of four feathering bearings. The director of maintenance (DOM) performed the task: laying out parts on a cart, performing installation including mast nut torque, and having a mechanic verify the torque. He then finished installation and had another mechanic verify the work. A company pilot performed a preflight inspection, ground functional checks, and three consecutive maintenance runs to balance the tail rotor. The accident flight was the first flight after completion.
The DOM reported that between the mast nut torque application and completion of the tail rotor assembly installation, he was “called out” to consult on two different aircraft repairs. He did not recall the elapsed time before resuming.
Wreckage Examination
Postaccident examination revealed that the tail rotor crosshead drive plate was not bolted to the tail rotor crosshead as prescribed in the maintenance manual. The two attachment bolts were missing, and no remnants were found in their threaded receptacles. The threads were undamaged with no signs of corrosion, deformation, smearing, or cross-threading.
Main rotor flight control continuity was confirmed from the cockpit to breaks in each rotor blade. Tail rotor control continuity was confirmed from the pedals to breaks to the tail rotor gearbox to the pitch control rod. Movement of the pitch change push-pull tube resulted in smooth movement of the pitch change rod, and the attached tail rotor crosshead drive plate moved with the pitch change rod but independently of the crosshead.
Relevant Manual Information
The Bell 407 Rotorcraft Flight Manual states that there is no single emergency procedure for all anti-torque malfunctions. Indications of loss of tail rotor thrust include uncontrollable yawing to the right, nose-down tucking, and possible roll of fuselage. Severity is affected by airspeed, center of gravity, power, and density altitude. For in-flight complete loss of tail rotor thrust, the manual calls for reducing throttle to IDLE, immediately entering autorotation, and maintaining a minimum of 55 KIAS during descent. It notes that the vertical fin may permit controlled flight at low power and sufficient airspeed.
The FAA Helicopter Flying Handbook indicates that an antitorque failure at high power and low airspeed results in severe spinning to the right. A mechanical control failure limits or prevents control of tail rotor thrust, usually from a stuck or broken control rod or cable, and autorotation is generally not required.
US Army Training Circular 3-04.4 explains torque effect and that improved rotor efficiency from directional flight (translational lift) makes the tail rotor more efficient, causing nose-left yaw (with counterclockwise main rotor) and requiring right pedal.
Post-Accident Action
As a result of this investigation, the operator developed a required inspection program, published and amended to the General Operating Manual, and submitted to the appropriate FAA Certificate Holder District Office.