The Occurrence
On 4 October 2021, a Kaman Aerospace Corporation K-1200 helicopter (registration C-FZVM, serial number A-94-0053) operated by Black Tusk Helicopter Inc. was conducting helicopter logging operations near Killam Bay in Jervis Inlet, British Columbia. The pilot was the sole occupant. After a mid-day break, the pilot resumed transporting logs from a cut block to an ocean log pen approximately 0.6 nautical miles northwest. At 1302:19 Pacific Daylight Time, the helicopter departed the cut block with three logs in the grapple. About 75 seconds later, it released the logs into the pen, entered a slow 180-degree turn, and began climbing back to the cut block. At 1303:42 PDT, the helicopter suddenly entered a rapid descent and, approximately four seconds later, struck the water within the log pen and sank.
The helicopter was equipped with a 406 MHz emergency locator transmitter (ELT), but no signal was received by search and rescue agencies because the ELT was submerged. The company, which had been in regular radio contact with the pilot, promptly initiated a search and contacted emergency services. During the search, portions of all four main rotor blades were recovered. The main wreckage was located using sonar eight days after the occurrence. The pilot was fatally injured.
Investigation Findings
The investigation determined that the helicopter experienced an in-flight breakup of the twin rotor system before impacting the water, based on the debris and damage patterns. Laboratory tests on the recovered main rotor blade fragments revealed that the departure of the servo flap afterbody on main rotor blade 0517B created an out-of-track condition. This caused a cyclic imbalance and a sudden vibration in the left main rotor system, leading to flutter in the other three rotor blades and failure of the left-pylon structure. Subsequently, a blade on the left rotor collided with a blade on the right rotor, resulting in the in-flight breakup of the rotor system.
Further examination indicated that a fracture of the bond joint between the inboard closeout and the servo flap afterbody on blade 0517B likely initiated a fatigue crack in the servo flap skin, which progressed until the afterbody separated in flight. The investigation noted that if the quality of the bond joint is inconsistent, the structural integrity of the servo flap can be compromised, rendering it unable to withstand normal aerodynamic loads.
Additional Safety Issues
Although the helicopter was equipped with an ELT, it failed to transmit because it was submerged after impact. The pilot's regular radio communication with the company enabled the local crew to quickly locate the occurrence site and begin searching. However, the investigation highlighted that aircraft operating over water without an automatically deployable ELT risk delayed search and rescue response.
The helicopter was not equipped with a flight data recorder or cockpit voice recorder, nor were they required by regulation. While other data sources provided significant information, the exact maneuvering in the final moments and the time between the last data point and impact could not be determined. The investigation noted that without on-board recording devices, the exact causes and contributing factors in fatal accidents with no survivors may remain unidentified.
Following the occurrence, Kaman Aerospace Corporation performed tests to verify the airworthiness of the servo flap and planned further evaluation of its fatigue capability. On 1 June 2023, the Kaman Model K-1200 K-MAX Maintenance and Servicing Instructions were revised to add instructions for repairing chordwise paint cracks in the bond line of the servo flap inboard closeout, with a note that the flap must be removed from service if the crack extends beyond the paint layer. On 19 July 2023, the Transportation Safety Board issued an Air Transportation Safety Advisory Letter to Transport Canada, informing it that in at least two fatal Kaman K-1200 accidents, a main rotor servo flap experienced fatigue fractures before catastrophic failure. Transport Canada stated it would monitor for additional cracking and, pending corrective actions from the FAA, may take interim action.