The TSB released a report on Friday that said the privately-owned de Havilland Beaver was facing the sun, and the glare probably prevented the pilot from seeing the looming treetops after the plane took off from Okanagan Lake in May 13, 2012.
The pilot had taken off from Pitt Meadows, about 40 kilometres east of Vancouver, in the afternoon with three passengers. After dropping off one passenger at Okanagan Lake, the plane headed towards Peachland for the return flight to Pitt Meadows.
As the aircraft flew near Highway 97C, it clipped the trees, crashed and burst in flames, the report said.
The pilot, 52-year-old Colin Moyes, as well as his two passengers, 81-year-old Peter Brooke Keate and his 79-year-old wife Inez Helen Keate, died. All three people were from West Vancouver.
The TSB report said an analysis done on the accident site determined that it would have been in the shadow just before the crash. As well, the pilot would have been staring into direct sunlight as it followed Highway 97C into higher terrain.
"When turning northbound, the pilot was probably still affected by disability glare, and possibly by a visual illusion," said the report. "Being in shadow, the treetops were probably not visible until the aircraft made contact with them."
The report also concluded that the pilot was flying at a lower altitude because the plane was heavy, and down-flowing air from the wind affected the aircraft's ability to climb higher.
The investigation ruled out aircraft malfunction or in-flight emergency as a cause of the crash because the plane was well maintained, and the constant ground speed and flight path suggested that Moyes had control of the plane. Moyes is also described as an experienced pilot with about 420 hours of flight time.
The single-engine de Havilland Beaver is a common aircraft used for bush flying.
The TSB says small aircraft face a greater risk when venturing into mountainous terrain with low visibility because they aren't required to have the same warning equipment as larger planes.
As a result of the investigation, Transport Canada plans to provide better information to pilots — including a new preferred route out of Okanagan Valley — to reduce the risk of crashes across the mountainous area. Pilots flying out of the airports in Penticton, Oliver and Osoyoos are also now encouraged to maintain an altitude of 1,500 metres before leaving the Okanagan Valley.