NYC96LA135

The pilot was doing aerial spraying of a cranberry bog, and had completed four passes before he executed a right turn to the north to begin the next run. After completing the turn, the helicopter began to spin to the right. After about three to four turns it stopped in a level hover, but then started spinning again to the right. After another three to four spins, it again stopped, and began a final spin to the right when it collided with the bog. Bell Helicopter Textron (BHT) published an Operations Safety Notice, in 1983, which dealt with unanticipated right yaw of the Bell 206 series. It stated that unanticipated right yaw could occur when maneuvering between hover and 30 MPH, and that a tail wind could reduce relative wind speed if a down wind translation occurred. It also stated that a loss of translational lift could result in a high power demand and an additional anti-torque requirements, which included high power demand situations such as low speed downwind turns. A local automated weather report indicated that the winds from were from 210 degrees at 6 knots. The pilot stated that the uncontrolled event initiated when he had completed a right hand application turn, and did not report a lateral cyclic displacement during the last application run.

On July 1, 1996, at 0600 eastern daylight time, a Bell 206B III, a helicopter, N444JB, was substantially damaged during an uncontrolled descent to a marsh near South Carver, Massachusetts. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed for the agriculture application flight that originated at the South Carver cranberry bog, about 0530. No flight plan had been filed for the flight conducted under 14 CFR Part 137.

In the NTSB Form 6120.1/2, the pilot stated:

"...departed a cranberry bog in South Carver with the first load of fertilizer of the day. After 4 passes over the bog, I began a 5th pass running south to north, which brought the aircraft over the pond on the north side of the bog. At the top of the turn I turned the aircraft to the right and at that point was unable to level or turn the aircraft to the left. At that point the aircraft banked and dove to the right and I attempted to relieve the right tank of the excess fertilizer and weight. I was unable to correct the situation and the aircraft continued to lose altitude and fly on it's right side. After several right hand turns the aircraft impacted the water. After impact I exited the aircraft and checked the right hopper and found approximately 300# [pounds] of fertilizer and only approximately 50# in the left hopper..."

Another helicopter pilot stated:

"...While being loaded...I saw...444JB spinning to the right with a slight nose low attitude with a moderate rate of turn. It made approximately three to four full turns before it stopped in which appeared to be a level hover. After approximately 2-3 seconds, the helicopter began a spin to the right with a nose low attitude once again. Again, after approximately 3-4 full turns to the right, [the pilot] stopped the spin in a somewhat level attitude only for 2-3 seconds before it began spinning again to the right. By this point, [the pilot's] altitude was getting low. From my vantage point, I could not see 44JB when it landed in the water..."

The helicopter was equipped with a lower mirror for the pilot to observe the chemical product as it was being dispensed.

A review of the operating limitations for the application system revealed that the maximum weight in each tank was limited to 400 pounds, and a single tank was limited to a maximum of 200 pounds lateral differential. Each chemical tank was equipped with a sensor connected to a warning light in the helicopter's cockpit. The warning lights were independent, and would illuminate when either tank was empty or not dispensing the product.

Bell Helicopter Textron (BHT) published an Operations Safety Notice, in 1983, which dealt with unanticipated right yaw of the Bell 206 series. It stated:

"...unanticipated right yaw may occur under certain conditions not related to a mechanical malfunction. These conditions may include high power demand situations while hovering, and/or when relative wind affects airspeed versus ground speed..."

It further stated:

"...When maneuvering between hover and 30 MPH: Be aware that a tail wind will reduce relative wind speed if a down wind translation occurs. If loss of translational lift occurs it can result in a high power demand and an additional anti-torque requirements. Be alert during hover (especially OGE) and high power demand situations such as low speed downwind turns.

The pilot stated that a local AWOS indicated that the winds from were from 210 degrees at 6 knots. The pilot also stated that the uncontrolled event initiated when he had completed a right hand application turn. The pilot did not report a requirement for a lateral cyclic displacement during the last application run.

In the Federal Aviation Administration Inspector's statement he said:

"...The helicopter was at the end of a swath run and turning to the right with a left quartering tail wind and low indicated airspeed prior to entering the uncontrollable turns which led to the crash. This is a situation that could possible have lead to the loss of tail rotor effectiveness. The helicopter remained submerged in 5 feet of water for 8 hours prior to being inspected by [the FAA]. Any fertilizer that had been in the dispensing units had dissolved...