VANCOUVER -- A small plane believed to have crashed last spring with two people on board is still missing seven months later, federal officials say.

A student, instructor and the 1972 Cessna 172M they'd been flying disappeared on June 6, during a training flight from Boundary Bay Airport in Delta, B.C.

A report summarizing the investigation, released publicly by the Transportation Safety Board of Canada Thursday, confirmed the plane and its occupants have still not been found.

The report also outlined what the TSB uncovered about the case.

The plane took off at 12:57 that afternoon, and turned east-northeast as it climbed to an altitude of 2,400 feet, the report says.

Seven minutes later, the instructor on board contacted an air traffic control tower in Pitt Meadows for permission to enter the control zone.

According to the TSB, someone working in the tower said the aircraft couldn't be accommodated, and directed the instructor and student to Langley instead.

One minute later, the instructor contacted Langley Regional Airport and was granted transit through its control zone.

"There were no further communications received from the aircraft," the TSB report said.

The investigation showed the plane started to descend at 1:09 p.m. as it flew over the Fraser River.

The TSB said radar contact was lost at 1:12 p.m., when the plane was about 9.7 nautical miles from the Abbotsford Airport, and about 200 feet above sea level.

One minute later, the plane struck a power transmission line that was strung across the Fraser River.

The report says witnesses told investigators they saw a splash in the river and a partially submerged plane. Someone called 911 six minutes after the plane hit the wire.

Mounties and other first responders went to the area, but could not find the plane. Months of search efforts, which involved boats, helicopters, divers and underwater imaging equipment turned up no evidence of the missing people or the Cessna.

They have still not been found seven months later.

It is not yet known what went wrong. According to the TSB, the weather was "favourable" that day. Although the plane was manufactured in the '70s, records suggested it was certified and maintained, and had no known deficiencies.

And, the report says, given the power lines' height above water, they shouldn't have been an obstacle for passing planes.

Lights for daytime use had been installed in the suspension towers near the crash site but were not activated. Investigators were not able to determine whether the instructor and student were aware of the lines.

BC Hydro has committed to activating the daytime strobe lights in 2021.

It is also not known why they were flying at such a low altitude, though it is permitted when training outside of a built-up area.

"Intentionally flying at a low altitude increases the risk of an accident," the TSB wrote.

"At heights below 90 metres… obstacles can be difficult to see as they may not be physically marked, or indicated on navigational charts."

Transportation safety officials said flying at a low altitude also reduces the margin of safety should a plane's engine fail or a pilot lose control. It also increases the risk of striking the ground or another obstacle.

There was no indication in the student's lesson plans that they'd ever practised low-altitude manoeuvres, or that any were planned.