NTSB Factual Report

On April 27, 2017, about 1330 eastern daylight time, a Robinson R44 II, N728CB, operated by Chesapeake Bay Helicopters, was substantially damaged during a collision with terrain while maneuvering near Newton, North Carolina. The commercial pilot and crewmember sustained minor injuries. The local aerial observation flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and a company flight plan was filed for the flight that originated from Concord Regional Airport (JQF), Concord, North Carolina, about 1225.

The pilot reported that he was performing a pipeline patrol at 500 ft above ground level and an airspeed of 70 knots. During the patrol, the crew observed a right-of-way infraction and circled the location at the same airspeed and altitude. While extending the circling pattern, the pilot felt a shudder in the controls while at the same time, the nose of the helicopter yawed right and the helicopter began to spin. He immediately lowered the nose in an attempt to increase forward motion, but the rate of spin increased. He then attempted to set up for an autorotation and avoid residences and utility wires. The helicopter subsequently impacted the ground and the pilot was able to shut down the engine and exit the helicopter.

The crewmember reported that while on pipeline patrol, they circled to photograph construction work. While circling, the helicopter lost control and spun two or three times before impacting the ground.

Examination of the wreckage revealed substantial damage to the helicopter. Tail rotor driveshaft continuity was confirmed from the tail rotor blades to the main rotor. Continuity was also confirmed from the left anti-torque pedal to the tail rotor. A section of right anti-torque pedal control tube was found bent and separated. The separated section of control tube was retained for metallurgical examination, which revealed that the separation was consistent with overstress due to impact forces. No preimpact mechanical malfunctions were identified.

The helicopter's most recent 100-hour inspection was completed on March 10, 2017. At that time, the airframe and engine had accumulated 1,873.6 total hours of operation. The helicopter had flown an additional 43.6 hours from the time of the inspection, until the accident flight.

The recorded wind at an airport located about 10 miles northwest of the accident site, at 1253, was from 190° at 8 knots.

Review of GPS data provided by the operator revealed that after completion of the first left circuit and the beginning of the second left circuit, the helicopter's ground speed slowed to about 1 mph at a GPS altitude of 1,223 ft (about 500 ft above ground level). At that time, the GPS track was indicating a northerly course, with an approximate 8-knot tailwind. The track subsequently indicated transition from a left circuit to a right turn.

The Federal Aviation Administration issued advisory circular (AC)-90-95, Unanticipated Right Yaw in Helicopters during February 1995. The AC stated that the loss of tail rotor effectiveness (LTE) was a critical, low-speed aerodynamic flight characteristic which could result in an uncommanded right yaw rate that did not subside of its own accord and, if not corrected, could result in the loss of aircraft control. It also stated, "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 9 of the AC covered reducing the onset of LTE. It stated:

"In order to reduce the onset of LTE, the pilot should: ... c. When maneuvering between hover and 30 knots: (1) Avoid tailwinds. If loss of translational lift occurs, it will result in an increased high power demand and an additional anti-torque requirement. (2) Avoid out of ground effect (OGE) hover and high power demand situations, such as low speed downwind turns. (3) Be especially aware of wind direction and velocity when hovering in winds of about 8 - 12 knots (especially OGE). There are no strong indicators to the pilot of a reduction of translation lift... (6) Stay vigilant to power and wind conditions."

Paragraph 10 of the AC addressed recovery techniques. It stated:

"a. If a sudden unanticipated right yaw occurs, the pilot should perform the following:

(1) Apply full left pedal. Simultaneously, move cyclic forward to increase speed. If altitude permits, reduce power. (2) As recovery is effected, adjust controls for normal forward flight. b. Collective pitch reduction will aid in arresting the yaw rate but may cause an increase in the rate of descent. Any large, rapid increase in collective to prevent ground or obstacle contact may further increase the yaw rate and decrease rotor rpm. c. The amount of collective reduction should be based on the height above obstructions or surface, gross weight of the aircraft, and the existing atmospheric conditions. d. If the rotation cannot be stopped and ground contact is imminent, an autorotation may be the best course of action. The pilot should maintain full left pedal until rotation stops, then adjust to maintain heading."

Additionally, Robinson Safety Notice SN-34 addressed aerial survey and photography flights, and provided cautions about such flights below 30 knots airspeed.

NTSB Probable Cause

The pilot's failure to maintain an adequate airspeed during out-of-ground-effect maneuvering at a low airspeed with a tailwind, which resulted in a loss of helicopter control due to a loss of tail rotor effectiveness.