TSB concludes investigation into Edson helicopter crash during wildfire efforts

The highly technical final report into the crash explains, among other things, that VRS, “occurs when a helicopter’s flight path, airspeed, and rate of descent coincide with the helicopter’s downwash. In normal flight, airflow from the main rotors is directed downward. In VRS, the tip vortices generated by the main rotors re-circulate through the rotor, adversely affecting lift.”

The Helicopter Flying Handbook published by the Federal Aviation Administration (FAA) of the United Sates, the report notes, identifies the following combination of conditions as being likely to cause VRS:

a vertical descent or nearly vertical descent of at least 300 fpm;
powered flight, typically within the range of 20-100 per cent engine torque; and
horizontal velocity slower than effective translational lift.

What occurred here, the TSB says, is that the helicopter was conducting a return flight to Edson Airport from a forest fire fighting staging area to the east.

Per the report: “When the helicopter was five nautical miles east of CYET, a flight of four Canadair CL-215T aircraft was approaching the airport from the west and intending to land on Runway 07, which was active at the time. It was reported that the wind was strong and gusting from the east-southeast. The occurrence pilot’s usual approach to the Range Helicopters hangar at CYET involved passing to the south of the town of Edson, Alberta, and then approaching the airport from the west. Upon hearing the intentions of the flight of CL-215T aircraft, the pilot, not wanting to delay the group’s arrival, decided to approach the airport downwind and to the north of Runway 07, between the runway and the taxiway, with the intent of conducting a tight right turn to align the helicopter into the wind (Figure 1).”

Figure 1. Occurrence helicopter’s flight path to Edson Airport (Source: Google Earth, with TSB annotations)

“As the helicopter approached between Runway 07 and the grassy area between taxiways A and B, the pilot began to slow down, eventually reaching a groundspeed of 30 knots. He noticed a pair of air tankers at the fire base ahead and to his right, and, not wanting to overfly them, he slowed down even more. The helicopter was in a descent at a rate between 300 and 500 fpm with a tailwind of 27 to 36 knots. Just before entering the right turn toward the hangar, the helicopter began an uncontrolled descent from between 50 and 30 feet above ground level (AGL). The pilot applied collective to reduce the rate of descent; however, the rate of descent increased. This scenario is consistent with a vortex ring state. The aircraft struck the ground and rolled onto its right side at 2005 hours.The pilot was able to extricate himself from the wreckage. There was no fire. The emergency locator transmitter activated.”

At the time, winds were gusting at 36 knots.

It had been reported that although visibility during the return flight was good, it deteriorated approximately 10 nautical miles east of CYET, before reducing to 1.5 statute miles in haze in the area of the airport. The pilot was aware of the wind condition, the TSB says.

The report, which the TSB notes is not to assign fault or determine civil or criminal liability, determined that the pilot had been on flight duty for seven days before the occurrence, during which time he flew 46.6 flight hours, equivalent to 85.5 duty hours. They had worked several 14-hour duty days, and had been flying for about 7.5 hours at the time of the crash.

The report says the company the pilot was flying for mitigated the risk posed by long hours by housing crews in hotels located near the fires, allowing more time for uninterrupted rest.

The TSB concludes that fatigue was “likely not” a factor in the crash.

The report goes on to conclude:

the pilot held a commercial pilot licence – helicopter and a valid Category 1 medical certificate. His total flight time was 1,901 hours. A review of his personal log showed time as pilot-in-command in a variety of light helicopters, mainly involving pipeline patrols. He had achieved 121 hours flight time in the AS350 B2, including 118 hours as pilot-in-command.
the helicopter’s weight and centre of gravity were within the prescribed limits
the helicopter was certified and equipped for daytime visual flight, as per the Canadian Aviation Regulations
at the time of flight, there were no documented defects in the helicopter’s journey log, which was recovered from the wreckage
a daily inspection had been done that day
The pilot underwent annual recurrent training and completed all computer-based ground training and flight training by the end of March 2023. The flight training included exercises in the recognition of and recovery from VRS.

“This investigation highlights the importance of approach planning and power management, particularly when conducting a downwind approach to a landing site,” the TSB says in its safety message to wrap up the report.

“Therefore, it is critical that helicopter pilots remain aware of and avoid flight conditions that can cause VRS to develop. Any potential time saved by attempting a downwind approach must be carefully weighed against the risks that it may present.”

The full report is available at tsb.gc.ca.

by Josh Hall | @Vancan19

TSB concludes investigation into Edson helicopter crash during wildfire efforts

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