The Transportation Safety Board has released its report into a fatal crash last year.
The crash happened midair on February 9, 2011 in the Mission area.
Four planes had taken off from Langley for a formation flight to Chilliwack, but two of the planes, both Cessnas, collided during a turn.
One of the planes fell into a slough, two people inside died.
The pilot of the other plane managed to land in a nearby field.
Bill Yearwood with the T-S-B says during the attempt to turn, one of the aircraft on the right lost sight of the lead aircraft, and while trying to re-engage, it collided with that lead plane.
"Re-engagement during a formation is very risky and in most cases, the plan should include a maneouvre that does not attempt to re-engage."
Yearwood says there was no plan on how to re-engage if the pilots lost formation.
He says there were no mechanical issues.