NYC96LA167

The pilot was conducting a powerline patrol, and at the request of the observer(s), he maneuvered the helicopter so they could take another look at a tower. According to the pilot, he was flying west, and the wind was from the west to northwest at 10 knots with gusts from 15 to 20 knots. He inadvertently slowed to 20 knots. As the pilot applied power and left pedal, the helicopter started a right rotation. He was unable to recover directional control, and was forced to autorotate into unsuitable terrain. The tail rotor struck a tree during descent. During the landing, the skids were driven into the fuselage. According to a chart in the flight manual, the critical wind azimuth area was from 050 degrees to 210 degrees.

On August 13, 1996, about 1240 eastern daylight time, a Bell 206-BII was substantially damaged when it struck the ground near Starks, Maine. The airline transport pilot and two passengers were not injured. Visual meteorological conditions prevailed and no flight plan had been filed for the power line observation flight which originated at Rangeley, Maine, about 1050 and was operated under 14 CFR Part 91.

In the NTSB Accident Report, the pilot reported that he was flying to the west. He further stated:

"...the observer spotted a problem with one of the structures and requested another look and asked for a slow pass. I turned downwind and set up to be on course into the wind at least three structures back from the support structure. The offset was 150-200 feet AGL up and to the left of the wires at 30 MPH so the observer, in the back, could get a good look."

"I scanned the wires to maintain offset and then looked inside. Airspeed had decreased to 20 MPH and I raised collective and added left pedal. The aircraft yawed to the right and I continued to add left pedal until it hit the stop. As the nose of the aircraft went through the wind line I had full left pedal applied and the yaw rate continued to accelerate. I could not apply forward cyclic at that time because of a taller tree line to the south. After one rotation I decreased pedal input then reapplied it to try and get good air to the tail rotor."

"The yaw rate continued to accelerate and the aircraft began to settle. I saw that the torque was jumping between 90 and 110%, the aircraft quit flying and began to settle into the power line right of way."

"The tail boom/rotor impacted a tree, and the yaw rate continued to accelerate. Once I was sure we were in the right of way below the wires and away from the trees I executed an autorotation. The helicopter stayed upright, nose downhill, right skid up on a rock. The pax reported that they were OK with no injuries and a normal shutdown was completed...."

In the NTSB Accident report, the pilot reported the winds were from the west/north west at 10 knots, with gusts at 15 to 20 knots.

Page 3-6C of the FAA APPROVED 206B Flight Manual has chart which shows the critical wind angle as between 050 degrees, through 210 degrees.

Page 3-6D of the FAA APPROVED 306B Flight Manual states:

"...AREA A (white area as shown on the hover ceiling charts represents hover performance for which satisfactory stability and control has been demonstrated in relative winds of 17 knots (20 MPH) sideward and rearward at all loading conditions...."

"...AREA B (yellow area) as shown on hover ceiling charts presents additional hover performance which can be realized in CALM WINDS or winds outside the CRITICAL RELATIVE WIND AZIMUTH AREA...."