MIDDLEBORO, MA, USA
N444GW
BELL 47G-5A
THE PILOT HAD MADE SEVERAL PREVIOUS AERIAL APPLICATION RUNS OVER A CRANBERRY BOG. AT THE END OF A SOUTHEAST RUN, THE PILOT STARTED A 'NORMAL AG TURN' TO THE RIGHT. AT THE COMPLETION OF THE TURN, AT AN ALTITUDE OF 30 TO 35 FEET, THE HELICOPTER BEGAN AN ABRUPT, UNCONTROLLED DESCENT TOWARD THE GROUND. THE PILOT APPLIED COLLECTIVE PITCH, WAS UNABLE TO ARREST THE RATE OF DESCENT, AND THE HELICOPTER COLLIDED WITH THE GROUND. NO MECHANICAL MALFUNCTION OF THE HELICOPTER ENGINE OR THE FLIGHT CONTROLS WAS DETECTED. WINDS AT THE ACCIDENT SITE WERE FORM 220 DEGREES AT 12 KNOTS. A WITNESS STATED THAT THE HELICOPTER APPEARED TO HOVER AT 30 TO 35 FEET, STARTED THE RIGHT TURN, THEN DESCENDED RAPIDLY TO THE GROUND.
On May 4, 1995, at 1145 eastern daylight time, a Bell 47G-5A, N444GW, operated by Wiggins Airways Inc., Norwood, Massachusetts, was substantially damaged when it struck the ground while maneuvering near Middleboro, Massachusetts. The commercial rated pilot received minor injuries. Visual meteorological conditions prevailed for the aerial application flight that originated at the application site. 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 that he had been spraying fertilizer on a cranberry bog in the Middleboro area. He further stated: ...I had made one pass from NW to SE and started a normal AG turn. Upon completion of the Ag turn and starting the pass the helicopter began an abrupt and uncontrolled rapid descent toward the ground. I tried to slow down the descent rate by pulling in collective pitch, but was unable to stop the descent rate before making contact with the ground. Upon making contact with the ground, the main blades I believe made contact with the tail boom and then the ground flipped the helicopter up on it's side... In a telephone interview with the Federal Aviation Administration (FAA) Inspector, and in his written report, he stated that the helicopter was on it's last application pass with less than 100 pounds of fertilizer on board. A witness reported to him that the helicopter was hovering with little forward airspeed about 30 to 35 feet above the ground. The helicopter initiated a right turn from the downwind when it descended rapidly and impacted the ground. Examination of the helicopter revealed that the fuel tanks contained about 15 to 20 gallons of fuel. No mechanical malfunction of the helicopter engine or the flight controls were detected. The United States Army Field Manual, Fundamentals of Flight, discusses a helicopter aerodynamic condition called "settling with power." The manual stated: Settling with power is a condition of powered flight where the helicopter settles in its own downwash. The condition may also be referred to as the vortex ring state. Conditions conducive to settling with power are a vertical or near-vertical descent of at least 300 feet per minute and low forward speed. The rotor system must also be using some of the available engine power (from 20 to 100 percent) with insufficient power available to retard the sink rate. These conditions occur during approaches with a tail wind or during formation approaches when some aircraft are flying in turbulence from other aircraft... The winds at the accident site were reported to be from 220 degrees at 12 knots.
the pilot's failure to maintain airspeed during a low altitude aerial application turn, which resulted in inadvertent settling with power and the subsequent collision with the terrain.
Source: NTSB Aviation Accident Database
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