A Transportation Safety Board report says a series of missteps during a formation-flying routine over B.C.'s Fraser Valley led to two deaths in February 2011.
The report says four small planes were practising the high-risk routine, and when the newest member of the team attempted to rejoin the formation he set off a mid-air collision.
The lead plane broke up in mid-air and crashed into a shallow slough, killing the 61-year-old pilot and his passenger.
The pilot of the second plane regained control and landed in a farmer's field.
As a result of the crash, Transport Canada has issued a safety bulletin on the hazards of formation flying.
The bulletin stresses pre-flight planning and reminds pilots to ensure they have the skill set to take part in formation flying.