A Helijet International Sikorsky S-76C++ was in cruise flight at 4,000 ft, carrying 12 passengers and a two-member crew between Vancouver (British Columbia, Canada) and Victoria when it was struck by lightning. The helicopter lost 3,144 ft in an uncontrolled rapid descent before the captain reestablished it in straight and level flight and continued to the destination.
No one was injured in the Oct. 24, 2023, accident, but the helicopter was substantially damaged.
In its final report on the accident, the Transportation Safety Board of Canada (TSB) said that, among the accident’s causes and contributing factors was the crew’s lack of awareness — despite their repeated checks of weather information — of the possibility of lightning.
“Meteorological conditions that are likely to produce helicopter-induced lightning strikes are not readily identifiable with current weather assessment methods,” the TSB report said. “As a result, although these conditions were present at the time of the occurrence, information regarding them was not available to the flight crew, and they were unaware of the possibility of lightning.”
The helicopter flew through conditions that were conducive to helicopter-induced lightning — a phenomenon in which the helicopter itself triggers a lightning strike, often in an area where there is little natural lightning activity, the report said.
The report explained that “[h]elicopters, like all aircraft, acquire a negative charge that is created by the frictional contact with the air during flight. The rapidly rotating main rotor and tail rotor blades will generate the greatest concentration of negative charge and are likely an entry point for the initial lightning strike. When the helicopter encounters a positively charged region of a cloud and the potential difference is great enough between the opposing charges, the helicopter can trigger a positive lightning strike.”
In this instance, the lightning strike carried a current that exceeded the certified design of the tail rotor blade assembly, and the exceedance led to the separation of the inboard tail rotor blade assembly.
Multiple Flights
The morning of the accident, the captain and the first officer (FO) arrived around 0515 local time at the Helijet hangar at Vancouver International Airport and prepared for departure on the first of several flights planned between the nearby Vancouver Harbour Heliport and the Victoria Harbour Heliport; preparations included a review of the available weather forecasts and other weather information. The FO was the pilot flying for all the early flights, including the accident flight.
The accident flight was the third leg on that morning’s schedule, following two instrument flight rules (IFR) flights from the Vancouver heliport to the Victoria heliport and back; the skies had been clear for both flights although there were clouds at 4,000 and 5,000 ft above sea level.
Before each of the three flights, the crew filed an IFR flight plan, calculated weight and balance, and reviewed current meteorological aerodrome reports (METARs) for the route. In preparation for the third flight, the helicopter was refueled before the 12 passengers boarded; after boarding, the captain provided a safety briefing.
The accident flight left the Vancouver heliport at 9111 local time and climbed, as directed by air traffic control (ATC), to 4,000 ft. The crew’s in-flight checks of weather information revealed no significant changes since the previous flight, but the helicopter entered clouds along the route, and as it approached Victoria International Airport and turned to a heading of 160 degrees, the weather display indicated precipitation.
At the same time, the helicopter encountered heavy rain and turbulence and then, at 0959:56, “the occupants heard a loud bang and saw a bright white flash that encompassed the helicopter,” the report said. “The flight crew immediately recognized that the helicopter had been struck by lightning.”
The autopilot, flight director, and all four electronic flight instrument system (EFIS) displays turned off. The EFIS displays quickly turned back on, but only two contained valid information; the autopilot and flight director remained off.
At 0931:17, some 21 seconds after the strike, the captain took the controls, and four seconds later, the helicopter began an uncontrolled rapid descent through clouds, dropping from 4,029 ft to 885 ft in the next 36 seconds with a left roll of up to 63 degrees and a downward pitch of as much as 44 degrees. At the time, the captain experienced spatial disorientation, which the report attributed to “the helicopter’s attitude …, the sudden loss of instruments and autopilots, the transfer of control, and the absence of visual references.” When the helicopter exited the clouds and the captain could see the ground, he stopped the descent, and returned the helicopter to an altitude above 2,000 ft.
The FO declared an urgency, told ATC they wanted to divert to Victoria International Airport, and requested vectors, but soon afterward, they cancelled the diversion and their IFR flight plan and proceeded to the Victoria heliport, where the helicopter landed at 0944. At the time, they were unaware of the damage to the helicopter, and “based on the information they had … regarding the airworthiness of the helicopter, the flight crew determined that the lowest-risk option was to continue the flight under visual flight rules to their intended destination,” the report said.
Unusual Attitude Training
The captain held an airline transport pilot license for helicopters and had 9,070 flight hours, including 970 hours on type. The FO had 580 flight hours, including 336 hours on type. During simulator training, both pilots had completed exercises for recovery from unusual attitudes, failure of the EFIS displays, and flight without access to key instruments.
The helicopter was manufactured in 2007. The day before the accident, an aircraft maintenance engineer had performed a scheduled inspection of the airframe and engines. The helicopter had no recorded defects, and there was no indication that any component or system malfunction had a part in the accident.
The main rotor and tail rotor blades are made of both metallic and non-metallic materials that have been identified as likely locations for a lightning strike to enter a helicopter, the report said, adding that “[a]s a result, the manufacturer integrated aluminum wire fabric into the blade construction so that the fabric will conduct a portion of the lightning current instead of the underlying blade structure.” This design is intended to disperse the energy of a lightning strike and limit effects at any specific location, the report said.
A post-accident inspection found that one of the helicopter’s tail rotor blade assemblies had separated from the helicopter and that the left side of the horizontal stabilizer and the engine cowl had been damaged. The inspection also found burn marks on one main rotor blade.
At the time of the accident, Helijet International operated a fleet of 18 helicopters and two airplanes under Canadian Aviation Regulations for commuter and air taxi operations and aerial work.
Image: Green Artist / shutterstock
This article is based on TSB Air Transportation Safety Investigation Report A23P0136, “Lightning Strike and Loss of Control; Helijet International Inc.; Sikorsky S-76C++ (helicopter), C-GXHJ; Sidney, British Columbia, 10 nm NE; 24 October 2023.
