(Jens Meyer/AP)

OTTAWA — In December 2014, Hydro-Quebec, Canada’s largest electric power utility, was hit with a crippling blackout at the start of winter. Traffic lights went dark, and more than 188,000 customers lost power, including Montreal’s McGill University Health Center.

The utility was forced to scramble to avoid a systemwide outage. Power exports to the Northeast United States were cut. Industrial users were asked to slash production, and the provincially owned utility was required to buy emergency power from neighboring utilities. Cost to the utility was estimated at $22 million.

Unlike most such incidents, however, the blackout was not weather-related or an act of God. As a Quebec court has heard, the power failure resulted from an act of sabotage by Normand Dubé, a 56-year-old pilot and inventor with a grudge against the utility, who used a small aircraft to hobble two massive power lines. Dubé was found guilty of three charges of criminal mischief in September.

Dubé was back in court this week in St. Jerome, Quebec, for a sentencing hearing in the unusual trial, much of which was held in secret because of national security concerns. Prosecutors argued the self-described “pilot to the stars” — his clients included several Quebec entertainers — should be given 10 years in prison for the attack.

Prosecutor Steve Baribeau told the court the pilot had attacked “the jugular and the spinal column” of the Hydro-Quebec power grid, according to the Canadian Press.

“What could be a worse way to destabilize a society than to cut electricity on such a large scale?” Baribeau argued.

The exact method used by Dubé to sabotage the lines, that transport electricity from hydroelectric dams in northern Quebec, is unknown because a publication ban was ordered on much of the testimony during the 27-day trial. Prosecutors sought the ban to protect national security and, presumably, to discourage copycats.

The 24-page judgment was also redacted, with references to the method used to disable the lines blacked out. However, Judge Paul Chevalier quoted an expert witness from Canada’s National Research Council as saying the technique had been used during conflicts in Iraq, Kosovo and Serbia and was “easily accessible on the Internet.”

A close reading of the judgment indicates that unidentified materials were dropped on the lines from the plane at three locations on the same day, prompting short circuits that ricocheted across the Hydro-Quebec grid.

What is known is Dubé had a long-running dispute with Hydro-Quebec over the utility’s efforts to access power lines that run through land he owned. The judge described the dispute in his ruling as “a deep-seated grudge” against the utility.

Despite having finished high school only, Dubé is a successful inventor, having designed a single-engine aircraft called the Aerocruiser and built a successful general aviation business.

He also invented a solar panel system and a machine to eliminate insects infesting commercial greenhouses that grow tomatoes, according to the judge.

Baribeau told The Washington Post that Hydro-Quebec initially had no idea what had caused the blackout, but two loggers in the area, near Mirabel airport north of Montreal, saw a small plane overflying the affected power lines, which then exploded in front of their eyes. The men called the utility, and the police were called in.

Armed with a description of the plane, an Aerocruiser designed by Dubé, the police obtained detailed radar information from Nav Canada, which runs the country’s air traffic control system. Dubé’s plane was identified as the culprit, Baribeau said.

“There was no ambiguity,” Baribeau told The Post. “There was no other airplane in the area at the time.”

Dubé’s lawyer told the court his client could not be considered a terrorist because he was not a follower of any political or religious ideology. Dubé admitted overflying the power lines on the day of the blackout but denied committing sabotage.

Meanwhile, the pilot is facing a lawsuit from Hydro-Quebec that is seeking to recoup the millions lost during the blackout. Dubé also is facing separate criminal charges resulting from a series of disputes he had with municipal officials over property evaluations. In one case, a municipal employee’s house was destroyed by fire, and another official was the victim of a Molotov cocktail attack.

The prosecutor has also asked that the judge seize Dubé’s plane.

Dubé has said he plans to appeal his conviction. The judge will decide on Dubé’s sentence in the sabotage case Dec. 10.