Accident Overview
On the day of the accident, a Bell 206B helicopter (serial number 8), operated by Helico Air Services Ltd., departed the company's base at Trenton Airport. The purpose of the flight was to identify and correct a minor vertical vibration reported by the company owner/operations manager, who had flown the helicopter earlier. This was the third maintenance flight; adjustments had been made by an aircraft maintenance engineer (AME) after two previous flights.
Shortly after departure, the helicopter was observed at low altitude in a nose-down spiralling descent near the airport. The wreckage was located in a wooded area east of the airport, approximately 275 feet from a road. The helicopter struck the ground in a steep, nose-down, left-bank attitude. The impact forces compromised the cabin integrity, and both the pilot and AME sustained fatal injuries. The helicopter was destroyed.
A student pilot at Trenton Airport heard an unintelligible radio transmission on the Trenton unicom frequency, prompting him to look out and observe the helicopter in descent. The student's instructor also heard the transmission. The accident occurred at about 1200 Atlantic daylight time in visual meteorological conditions, with light easterly winds.
Aircraft Information
The Bell 206B was manufactured in 1967 and exported from the United States to Canada in 1977. Originally powered by an Allison 250 C18 turbine engine, it was converted to an Allison 250 C20 in 1980. Helico Air Services Ltd. had operated the aircraft since the company's inception in 1993. The helicopter was equipped with an engine-out warning system (light and horn), dual flight controls, and hydraulically boosted anti-torque pedals. It was not equipped with a low rotor rpm warning light or horn, nor was one required. At the time of the accident, the aircraft had accrued 8,471.7 total flight hours and 81.5 hours since a 200-hour scheduled maintenance inspection on 19 December 1997. Fixed floats and new main rotor straps had been installed on 5 March 1998. A review of technical records indicated the helicopter was certified, equipped, and maintained in accordance with existing regulations.
Flight Crew
The pilot began his flying career with the Romanian military in 1980, flying Allouette III and Puma helicopters. After leaving the military in 1990, he spent five years in Germany in non-aviation roles. He received Canadian Commercial Helicopter license in June 1996 after 17.6 hours of initial training on the Bell 206. He began flying for Helico Air Services in 1997 and received additional Bell 206 training in November 1997. He was certified to fly Hughes 300 and Bell 206 helicopters. His Transport Canada file indicated about 1,034 hours total helicopter flight time, with approximately 124 hours on the Bell 206. His personal logbooks recorded about 1,900 hours (mostly on the Allouette), but supporting documentation was unavailable.
The AME received his maintenance license in 1991 (helicopter) and was endorsed on the Bell 206 in 1992. He had been employed by the operator since 1993.
Accident Sequence
On the day of the accident, the AME removed the cyclic and collective control sticks from the left seat position, leaving the anti-torque pedals installed. The control sticks are removed by unscrewing a retaining collar at the stub shaft base. Protective covers for the stub shafts were not installed. There was no regulatory requirement to install these covers, but prudent practice would preclude flying with them off and the dual anti-torque pedals installed during main rotor blade strobing.
The helicopter impacted the ground approximately 3,500 feet east of the departure runway end. The descent through trees resulted in localized tree damage above the wreckage. The fuselage came to rest in an approximate 45-degree nose-down, 50-degree left-bank attitude, with debris primarily within a ten-foot radius. The fuel bladder was punctured, saturating the ground; there was no post-crash fire. No evidence of bird strike or pre-impact structural failure was found. The forward cockpit was penetrated by a tree fork, compromising the area occupied by the pilot and AME. The AME wore only a lap belt; the pilot wore both lap belt and shoulder harness. Impact forces were not survivable. Autopsy revealed the pilot sustained multiple fatal injuries and a compound fracture to his lower right leg. Toxicology tests were negative for both individuals.
Investigation Findings
The helicopter's mast fractured below the trunnion drive splines, consistent with torsional overload. Flight control push/pull tubes exhibited overload fractures from impact. Rotor blades showed low rpm impact damage. The engine, transmission, mast, hydraulic servos, and cockpit instruments were examined further.
The emergency locator transmitter (ELT) did not activate; its switch was found in the OFF position. There was no indication it had been armed before the flight. The Bell JetRanger checklist references "ELT--Armed and Secure." The ELT tested serviceable at the TSB facility.
A work paper indicated the AME made minor adjustments to the main rotor blade pitch links after previous flights. The procedure was routine, and the AME was qualified. The pitch link adjustments were not contributory to the accident. The aircraft's weight and center of gravity were within limits.
A detailed engine examination at Standard Aero revealed the engine was operating at impact. Metal particles from the centrifugal compressor scroll were found on downstream nozzles. Engine accessories functioned normally. The freewheel assembly's outer race stub shaft spline was fractured due to torsional overload.
Instrument examination showed: engine-out warning light not illuminated; dual tachometer indicated main rotor rpm (Nr) at 67% and power turbine rpm (N2) at 73%; indicated airspeed 27 mph; attitude indicator showed a left 30-degree roll.
The four hydraulic servo actuators were bench tested. The two cyclic servos and tail rotor servo performed normally; the collective servo was unserviceable due to impact damage.
Fixed floats increase drag compared to skid gear. Conversations with other Bell 206 pilots indicated that maneuvers increasing the floats' cross-sectional profile could result in uncontrolled deviations.
The investigation referenced two 1967 Bell 206 incidents: one involved inadvertent full left rudder pedal application during forward flight causing a rapid left yaw and right roll; another involved pedal "creep" leading to a fatal accident. Flight tests confirmed that large anti-torque pedal movements could cause loss of control at some speeds.
Verbal reports of rotor rpm decay due to less than full throttle at take-off were not corroborated by a database review.
Free-turbine engine characteristics of the Allison 250 C20 require maintaining power turbine and rotor speed at full RPM via gas producer speed variation.
The investigation was unable to determine the reason for the loss of control.