TORONTO - Investigators are looking into whether a pilot who died along with three others when his small plane crashed Thanksgiving weekend in a vast Ontario park was cleared to fly at night, a Transportation Safety Board of Canada spokesman said Wednesday.

Pilot Kevin Houle, his wife Lorry Lemaire Houle, both 50, were killed in the crash Saturday along with their daughter Emily Houle and her boyfriend Micheal Rollins, both 17. They were returning home to Sudbury when Houle's Piper PA-28, a four-seat, single-engine plane, struck several trees and went down in Algonquin Park.

The high-impact crash near Devine Lake saw the plane break into several pieces, leaving a debris trail 90 metres long.

The flight plan Houle filed with NavCanada was for a direct trip from Kingston to Sudbury, leaving at 4:30 p.m. and arriving two hours and 15 minutes later.

Bryce Fisher, manager of standards and performance at the board, said Wednesday it appears the pilot left later than he intended. Preliminary information indicates the plane actually departed Kingston at 6:23 p.m., which would have meant Houle was flying in the dark, Fisher said.

"It is unknown and we're looking at this at this point whether or not Mr. Houle had a night endorsement," said Fisher.

Houle's pilot licence specified he comply with visual flight rules, which require the pilot to be able to see outside of the cockpit to control the plane, and did not permit him to fly relying on instruments only.

"We do know he does not have an instrument endorsement. But he may have had a night endorsement. We're not sure at this point. We're looking to confirm that," said Fisher.

Both night and instrument endorsements require additional training.

A signal from the emergency locator transmitter on the plane was picked up at 8:52 p.m. by search and rescue personnel at Trenton, Ont.

"The reason why I believe we're mentioning the fact he did not have an instrument endorsement is that he did not have the choice in terms of being able to go above the cloud, if you will, at the time if there was inclement weather," Fisher said.

The board believes the pilot did get a weather briefing in Kingston prior to departure, said Fisher, who added a frontal system moved through the Sudbury area much quicker than originally forecast, and a mixture of rain and snow was falling.

It's not known if the mixed precipitation was falling at Houle's crash location or if that was a factor in the tragedy, or whether Houle would have been able to obtain updated weather forecasts in flight, he said.

The board is also trying to obtain radar tracking reports to determine whether the pilot altered his route as well as maintenance records on the plane, which was manufactured in the U.S. in 1968.

The plane was registered to the Houle family's mining business, Tracks & Wheels.

On its website, Tracks & Wheels says all its branches will be closed to the public on Friday and Saturday in commemoration of Houle and his family.