History of Flight
On August 1, 2009, at approximately 1656 eastern daylight time, a Eurocopter EC 130B4, Isle of Man registration M-BOAT, was substantially damaged during a forced landing on the water near Deer Isle, Maine. Visual meteorological conditions prevailed, and no flight plan was filed for the local personal flight, which had departed from a privately owned motor yacht. The certificated private pilot and the three passengers sustained minor injuries. The flight was conducted under 14 CFR Part 91.
According to a representative of the pilot, the flight departed the motor yacht about 1650 and flew along a shoreline at approximately 400 feet above mean sea level. The pilot began maneuvering the helicopter, and it started losing altitude. Prior to impact with the water, the pilot deployed the emergency skid-mounted floats to prevent the helicopter from sinking.
An eyewitness reported that the helicopter appeared to hover, pointing roughly east, then suddenly spin and face west, after which it tilted and spun around while losing altitude.
In a written statement, the pilot reported entering an out-of-ground-effect hover and initiating a left pedal turn. He stated that the helicopter turned faster than commanded, he was unable to regain authority, and that the accident was entirely pilot error with no mechanical malfunction.
Personnel Information
The pilot, age 66, held a private pilot certificate with ratings for airplane single-engine land and rotorcraft-helicopter. His most recent FAA third-class medical certificate was issued on June 4, 2009. He reported 1,180 total flight hours, 680 hours in rotorcraft, and 55 hours in the accident helicopter make and model.
Aircraft Information
The helicopter was manufactured in October 2005 and its logbook was established on October 25, 2005. On August 26, 2008, it underwent a 50/100/annual/star inspection at 77.1 total aircraft hours. A six-month phase inspection was completed on January 22, 2009, at 83.4 total hours and 101 cycles. The engine, a Turbomeca Arriel 2B1 turboshaft, had accrued 113.1 hours since new and 137 cycles as of June 30, 2009. The helicopter featured a three-bladed, clockwise-rotating main rotor system.
Meteorological Information
The 1655 recorded weather observation at Knox County Regional Airport (RKD), Rockland, Maine, about 22 miles southwest of the accident location, indicated wind from 220 degrees at 8 knots, visibility 10 miles, few clouds at 7,000 feet agl, temperature 25°C, dew point 17°C, and altimeter 30.03 inHg.
Wreckage and Impact Information
The helicopter was examined at the manufacturer's facility on November 12, 2009. The tail boom exhibited impact damage and main rotor blade strikes. The right horizontal stabilizer, fenestron, and fin had damage consistent with main rotor blade impact. The left horizontal stabilizer showed impact damage. The drive system components displayed signature marks similar to impact damage.
Flight control continuity was confirmed from the cockpit through the tail rotor system and from cyclic and collective controls to the actuators mounted on the main transmission. The transmission had been removed before examination. Control tubes connecting the swashplate to the hub were fractured due to overload from impact. The transmission deck, mounting points, and struts were severely damaged.
The engine was displaced from its normal mounted position. During follow-on investigation, the engine gas producer and power turbine rotated freely, but leading edges of gas producer blades were damaged. The lower engine exhaust duct was dented inward with paint transfer marks. Magnetic plugs and the engine chip detector showed no metallic particles. Fuel and oil filters were free of debris.
The cabin structure exhibited impact damage, and doors were restricted from moving or latching properly. Seats did not show signs of attenuation from vertical impact forces.
No evidence of pre-impact mechanical failures or malfunctions was found during the examination.
Additional Information
The Rotorcraft Flying Handbook describes unanticipated yaw as an uncommanded yaw rate that does not subside and can lead to loss of control, referred to as loss of tail rotor effectiveness (LTE). For clockwise-rotating main rotors, LTE occurs to the left.
FAA Advisory Circular 90-95 states that LTE is a critical low-speed aerodynamic characteristic resulting in an uncommanded rapid yaw rate. It is not related to maintenance malfunction and can occur in single main rotor helicopters at airspeeds less than 30 knots. The circular notes that maneuvers requiring high power at low airspeed with a right crosswind or tailwind may cause unanticipated left yaw. It advises avoiding tailwinds, out-of-ground-effect hover, and high-power situations when maneuvering between hover and 30 knots, and staying vigilant of wind conditions.
Eurocopter Service Letter No. 1673-67-04 describes scenarios where a pilot initiates a left turn near the ground, the rotation increases, and applying right pedal may not stop it. Increasing collective pitch further accelerates the leftward rotation, leading to loss of control.