only to have the bucking intensify, leading him to sus- pect ground resonance. He increased fuel flow but did not advance it fully or lock it into its flight gate before raising collective, and neither the engine nor main rotor rpm reached their flight-governing ranges before the heli- copter lifted from the pad. The helicopter yawed and drifted to its left as engine rpm spooled up while the main rotor rpm decayed. Two minutes after engine start, the ship descended into the hillside and tumbled down the slope. The pilot—who was wearing his four-point harness but no helmet—man- aged to extricate himself from the wreckage after the
Professional pilots—particularly those operating in remote locations and extreme environments—can develop a tolerance for apparently benign aircraft anomalies. But discrepancies as seemingly trivial as a burned-out indicator lamp can become the kind of emergency that requires quick recourse to memory items if the wrong thing happens at the wrong time.
engine shut down. He walked back to the tower’s ser- vice building where his passenger administered first aid. After the pilot reported the accident, a company heli- copter dispatched from Fort Simpson arrived about 3:00 p.m. Both men were initially flown to Yellowknife. The pilot was subsequently airlifted to Edmonton for treat- ment of injuries including a badly broken arm. Six months later, he was back at work but had not yet returned to flight duty.
The Pilot The 5,277-hour commercial pilot had 2,017 hours in AS350s, with 6.5 hours in the previous week and 11.7 in the preceding 90 days. He held a Category 1 medical certificate and had completed recurrent training in the AS350 the month before the accident. His age has not been reported.
The Aircraft The AS350 B2 has a fully articu- lated, three-bladed main rotor powered by a single 732-horse- power Turbomeca Arriel 1D1 tur- boshaft engine. Its Starflex rotor head provides full articulation without hinges or lead-lag damp- ers; instead, flexible thrust
72 ROTOR WINTER 2019
bearings at the inboard ends of the mounting sleeves allow the blades to flex, flap, and move in the lead-lag axis, while elastomeric frequency adapters at the sleeves’ outboard ends provide damping. The accident aircraft was manufactured in 1989 and had served for 46,214 cycles comprising 11,005 hours of flight time. Its landing gear featured two vibration-absorbing sys-
tems: flexible steel strips extending downward from the aft ends of the skids, and hydraulic dampers between the front horizontal crosstubes and the fuselage. After the accident, the operator tested the damper assem- blies. The right damper (which had seen 1,395 hours of service compared to the left damper’s 3,001) failed the initial functional test, then passed after overhaul. The his- tory of the accident sequence, however, makes it seem unlikely that inadequate damping was a factor. Four days before the accident, in order to hangar the
aircraft overnight, all three main rotor blades had been removed by a technician with the assistance of the same pilot. After they were reinstalled the following morning, the pilot did a ground run and noticed increased vibration.
Although vibration analysis equipment was available at the site, vibration levels were not measured, nor were blade tracking and balance assessed as required by the aircraft’s maintenance manual. Furthermore, the removal and reinstallation of the main rotor blades weren’t recorded in the journey log, contrary to Canadian Aviation Regulations. Investigators learned that the main- tenance shop routinely removed and remounted blades without making the required logbook entries. The vibrations continued throughout the six hours the
pilot flew the helicopter during the intervening three days. “During this time,” according to the Transportation Safety Board of Canada’s (TSB) report, “no action was taken to verify or rectify the vibration and no aircraft jour- ney log entries were made.” With no measurements having been recorded, the preacci- dent tracking and balance status of the rotor could not be determined.
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The Response Following the accident, the opera- tor’s parent company emailed its pilots and maintenance personnel to remind them of the require- ment to document all removals and reinstallations of rotor blades in the journey logs. It also insti- tuted an audit procedure to more
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