Brad Serwa said he was driving on Highway 97C near Kelowna with his family at about 7 p.m. Sunday when they saw the plane about 60 metres above the road and angling toward the valley.
Serwa pulled over and called 911 as the family watched the plane descend.
"Then there's a puff of smoke and I said, `Oh crap, it's gone down.' And then within about a minute after we saw the smoke we ended up seeing flames and then the trees started catching on fire."
Serwa, whose family called 911, said Monday it appeared as if the plane’s engine was running at the time of impact.
Three people died in the crash.
"Our information is that, tragically, none survived the accident," said Transportation Safety Board spokesman Bill Yearwood.
He confirmed the de Havilland Beaver aircraft went down only minutes after takeoff from Okanagan Lake, near the community of Peachland, 25 kilometres southwest of Kelowna.
The aircraft was heading to its home base of Pitt Meadows, about 40 kilometres east of Vancouver, when it slammed into a steep, wooded hillside along Highway 97C and caught fire.
Five people were initially thought to be on the plane before new details emerged about the passenger list, Yearwood said.
"There were four on board when they left Pitt Meadows. It had originally planned to have five, but plans changed, and one was left in Kelowna, so three were on the return flight.
"We know the aircraft was returning (to Pitt Meadows) and it was close to the summit of the pass but there is no information to help us, at this point, as to what the pilot was experiencing."
The coroner and three TSB inspectors arrived at the crash site Monday, and Yearwood said there was little information about the victims or the aircraft.
He said they would analyze the wreckage and the damage to nearby trees to determine if the aircraft had power when it hit the ground.
"We just know that it was privately registered. We don't know who was onboard the aircraft, even if the owner was onboard."
A final report on what could have caused the crash will not be released for several months.
The single-engine Beaver de Havilland is a common aircraft used for bush flying.
"It's been operating for over 50 years in the civilian world and spent many years in the military world as well," Yearwood said.
"This particular one was equipped with floats with amphibious landing gear so it could land on land or in the water." (CKFR)