12/15/2017 10:20 EST | Updated 12/15/2017 12:42 EST

Hydro One grounds helicopter crews after crash, holds vigils for workers killed

TORONTO — One of Canada's largest electricity companies has grounded its helicopter fleet as investigators work to determine what caused a chopper crash that killed four of the utility's workers in eastern Ontario.

Hydro One's eight helicopters will not operate until a thorough review of safety protocols and equipment is complete, CEO Mayo Schmidt said Friday, noting that the measure was standard procedure after any serious workplace incident.

None of the four men on board the Aerospatiale AS350-B2 chopper survived after the helicopter went down shortly before noon Thursday in Tweed, Ont., about 90 kilometres northwest of Kingston, Ont. Hydro One said the crew had been completing work on a transmission tower.

"It is a time of emotion and shock for all of us at the company," Schmidt said, adding that there was no timeline for when the utility's helicopter fleet would go back to work.

The company held candlelight vigils at its offices across the province Friday morning and said most ground crews would be standing down from their jobs until Monday. Workers will still respond to any reports of power outages, it said.

"We are not going to leave people without power," Schmidt noted. "No one will have to wait any longer than normal if there is a loss of power in their community or their area."

The company is supporting employees and families affected by the crash with a wide range of services, including grief counselling, 24-hour hotlines and help making funeral arrangements, Schmidt said.

"As we always do, our family at Hydro One has pulled together," he said, adding that teams have been dispatched to assist affected family members.

The names of those who died have not been released.

The Power Workers Union said one of the workers killed had been one of its members, while the three other employees were members of the Canadian Union of Skilled Workers.

Investigators from the Transportation Safety Board are leading the probe into the crash. Hydro One said it had sent specialists to help the TSB with their work.

The TSB said investigators would be looking at a wide range of factors to determine a possible cause of the crash, including pilot records, aircraft maintenance records and aircraft history.

The single-engine AS350 is a utility helicopter often used for corporate purposes and by police.

Hydro One has four of those choppers in its fleet, as well as three Airbus AS350-B3 helicopters and one Airbus AS355-NP.

In July 2007, the same model clipped a guy wire in northern Ontario and crashed, seriously injuring a Hydro One worker and the pilot. And in January 2015, an AS350 crashed in Saskatchewan during hydro cable stringing, seriously injuring the pilot. In both cases, pilot error was to blame.