Federal aviation officials are investigating a harrowing near miss incident earlier this year, in which a jet used by the Canadian government to shuttle VIPs nearly collided with a passenger airliner over British Columbia.

RCMP officers are seen outside a CC-144 Challenger jet. (CBC)According to the Transportation Safety Board, the Canadian Forces CC-144 Challenger jet was flying eastbound on April 24 to Ottawa from Vancouver with an unknown number of passengers on board. An Emirates Boeing 777, which can carry up to 266 people, was flying from Los Angeles to Dubai.

The government's fleet of Challenger jets is reserved for high-level officials, including the prime minister and Governor General, as well as foreign dignitaries who use it to fly in utmost security.

Both aircraft were cruising at about 11,200 metres (37,000 feet) when their collision avoidance systems sounded, indicating the two planes could slam into each other.

The Emirates plane quickly climbed, while the government jet performed a dive. The planes passed each other within 213 metres (700 feet) vertically, breaking the "safety bubble" of 300 metres (1,000 feet) around aircraft.

Harper not on board: PMO

Prime Minister Stephen Harper is seen boarding a CC-144 Challenger jet operated by the Canadian Forces. The Prime Minister's Office confirmed Harper was not on board the April 24 flight. (CBC)But why the two aircraft came so close to each other has not been determined, said Bill Yearwood, the TSB's Pacific regional manager of air investigations.

"The reason for the investigation is to answer the question of why the aircraft were on a conflicting course and why the action taken by the controllers or pilots weren't sufficient to avoid penetrating the safety bubble," Yearwood told CBC News.

The Prime Minister's Office confirmed to CBC News that neither Prime Minister Stephen Harper nor any of his cabinet was on board the aircraft that day.

But the Canadian military won't say who was on board the flight. It operates the planes and refuses to reveal the passenger manifest.

According to one airline industry official, whoever was on board may owe their life to the collision avoidance system.

"They're one of the top-notch tools of our trade to prevent accidents nowadays, and there are lots of examples of where they have proven totally successfully, including the one recently," said Len Aalders of the Air Transport Association of Canada.

The Transportation Safety Board report won't be complete for several months and will not investigate who was on board the Challenger during the incident.