Northwestel Inc. is continuing its investigation into last Thursday's massive outage that knocked out communications across the Yukon, company spokeswoman Emily Younker said today.

"We do an investigation after every outage, but the size of this one was quite different so it's going to take a little longer,” she said.

Northwestel's system switched to backup batteries and diesel generation following a grid-wide power failure caused by a tree falling on a main transmission line at 11:10 p.m. Wednesday.

Failure of Northwestel's system occurred at approximately 4 a.m. Thursday, as Yukon Energy was completing full restoration of the grid.

Company officials said later that day that normally the diesel generator remains operable for about 30 minutes after grid power is restored. They were not sure if the failure occurred as the transition to grid power was occurring.

In addition to the loss of land lines and 911 service across the Yukon for more than six hours in some areas, cellular and Internet service were down as well.

Cable phone service but not regular phone service went down in Yellowknife, and the long distance service in Inuvik and other Mackenzie Delta communities was off and on, Younker explained.

She said DSL Internet service in Nunavut was also out.

The outage prompted calls from the Whitehorse Chamber of Commerce for Northwestel to modernize its technology to ensure back-up systems are stable.

Many Yukon businesses with an ADSL connection to the Internet lost service for most of the day, and consequently lost a lot of money, chamber president Rick Karp told the Star Friday.