MONTREAL - A teenager is being hailed as a hero for saving his great-uncle after their float plane crashed in northern Quebec, killing three other family members and the pilot.

Initial reports from the Transportation Safety Board suggest the Beaver float plane slammed into the side of a mountain Friday in Quebec's Lac-Saint-Jean region.

Investigators are looking at whether the thick fog the plane encountered caused the crash. There had been stormy weather in the area.

The plane was carrying five members of the Bernier family and the pilot when it went down in a densely wooded area in Chute-des-Passes, about 250 kilometres north of Chicoutimi.

The crash killed pilot Gabriel Boivin, who would have turned 59 on Saturday.

Michel Bernier, his 13-year-old son Louis, both of Chambly, Que., and his uncle Rejean Bernier, who lived in Saint-Joseph-de-Beauce, Que., also died.

Fifteen-year-old Simon Bernier escaped with minor injuries. The teen's other great-uncle Pierre Bernier of Montmagny, Que., was severely burned in the crash and remained in hospital Saturday night.

Bernier's wife, Marcelle Guay, told media outlets that Simon was a hero for pulling his great-uncle from the wreckage.

Transportation Safety Board investigators spoke to one of the survivors on Saturday to piece together what might have happened.

Two investigators will walk into the woods to the disaster scene on Sunday where they will spend the day gathering clues on the cause of the crash.

"All day their priority will be to look at the accident site, the wreckage, anything they can take into account for the investigation," Transportation Safety Board spokeswoman Chantal Laflamme said Saturday night.

Investigators will also look at whether a mechanical breakdown may have been to blame.

The de Havilland DHC-2 plane, operated by Air Saguenay, left from Lac-Des-Quatre, around 10:30 a.m. Friday and was headed to Lac Margane, an area popular with fishermen.

The last communication from the pilot said the plane had run into bad weather, said Laflamme.

The joint rescue co-ordination centre at CFB Trenton, Ont. received a call around 3 p.m. Friday saying the plane was overdue.

A CFB Trenton, Ont., spokeswoman said four military aircraft were dispatched to search for the plane -- one from Quebec, one from Greenwood, N.S. and two from Trenton.

Crew aboard a Hercules aircraft found the wreckage about 5 p.m. Friday. Rescue teams later found four men at the crash site with no vital signs and two in need of immediate medical attention.

Friday's incident was the third plane crash to claim lives in Quebec in the past three months.

On June 23, a small plane went down near the Quebec City airport after the pilot reported an engine failure. All seven people on board -- five passengers and two crew -- were killed.

In May, another plane crashed in nearby L'Isle Aux Grues, killing four people. That flight slammed into an embankment 15 minutes after takeoff and burst into flames.