In the U.S., there are about four or five fatal crashes by private aircraft every week, according to the National Transportation Safety Board. On May 7, a Grumman AA5 single-engine plane en route from St-Mathieu De Beloeil, Que., to Markham, Ont., crashed 40 kilometres south of Peterborough, killing the pilot.
Five days later, on Saturday morning, a mid-air collision near St. Brieux, Sask., between a Piper PA-28 Cherokee and a Lake Buccaneer amphibious plane killed all five people on board the two aircraft.
On Sunday evening, a de Havilland Beaver float plane crashed southwest of Kelowna, B.C., killing three people.
It is the mid-air collision in particular that has friends and family of the pilots killed, as well as other pilots, speculating about what could have happened.
The two planes were on near right-angle flight paths, but investigators are not clear yet whether they were still at 90 degrees to each other before the crash.
Peter Hildebrandt, an investigator with the Transportation Safety Board (TSB), told CBC Radio's Sheila Coles that the wreckage indicates that the planes definitely collided.
The TSB has just begun what will be a relatively involved investigation to try to figure out how the crash could have happened and it may be "months down the road" before it has any kind of answer to that question, Hildebrandt said.
Other mid-air collisions in Canada
On Feb. 9, 2011, four Cessna planes were flying in formation near Mission, B.C., when the plane in the rear crashed into the one in front. The two locked together and started spinning to the ground from a height of less than 1,000 metres.
The rear Cessna broke free and was able to land safely but the other plane crashed into a slough, killing the pilot and a passenger.
In 1999, the TSB investigated another mid-air collision, which happened near Penticton, B.C.
Over the past 10 years, the TSB identified 17 mid-air collisions in Canada. Eight involved some form of formation flying, three were in practice training areas and six were in uncontrolled air space.
How planes avoid each other
In Canada and the U.S., planes that carry at least 15 and 10 passengers respectively must have collision avoidance systems.
Such systems indicate the position of all aircraft within a selected range. The better ones even tell pilots how to manoeuvre to avoid the other aircraft.
Some small planes have systems on board to alert pilots, but in the CBC interview Hildebrandt said the TSB had yet to determine whether that was the case for either plane in the Saskatchewan collision.
Even without a system, he said there are still three ways pilots keep their planes apart:
By radio calls when arriving or departing an area to alert others to their presence.
By travelling at different altitudes, depending on the direction of the flight.
By being on the lookout for other aircraft.
As for tracking the radio communications, Hildebrandt said some of the frequencies the pilots may have used "may not have been recorded anywhere."
Tom Ray, the general manager of the Regina Flying Club, where one of the pilots killed in the crash was a member, told CBC Radio's David Gray that, "a split second would have made all the difference" in avoiding the collision near St. Brieux.
Ray added that the protocol for pilots to follow was that if you see an aircraft, "the aircraft on the right has the right-of-way."
Private planes at higher risk
In Canada the accident rate for private (including corporate) planes was 28.4 per 100,000 flying hours in 2002. That rate is much higher than the rate for commuter planes and airliners but the rate has been dropping over the years.
According to a 2002 TSB report, "the generally accepted factors that contribute to these higher accident rates include less stringent aircraft certification standards, reduced pilot training requirements, lower pilot experience, higher instances of single-pilot operations, greater proportions of time spent in low-altitude VFR operations, and more frequent use of small airports and landing strips that are not equipped with navigation and landing aids."
In 2011, there were 224 accidents involving single engine aircraft in Canada, 29 of them fatal.
In the U.S. in 2010, general aviation aircraft were involved in 1,435 accidents, 267 of them fatal. General aviation excludes passenger planes, cargo planes, air taxis, air medical and air tours.
A USA Today analysis in 2006 of NTSB data found that one-third of fatal recreational plane crashes were triggered by a loss of control and one-quarter occurred during aggressive manoeuvring.
Pilot inexperience is also a key factor. The newspaper found that 45 per cent of fatal crashes involved pilots with 100 hours or less flight experience in the specific model.
Overall, "as many as nine out of 10 private plane accidents are attributed to human error, Alan Levin and Brad Heath wrote in USA Today.
Mid-air collisions and airliners
Mid-air collisions involving at least one airliner have been quite rare in the last few decades.
On April 8, 1954, near Moose Jaw, Sask., a Trans-Canada Airlines flight collided with a military aircraft, resulting in 37 deaths.
Two years later, in what was then the worst civil air accident in the U.S., two planes collided over the Grand Canyon in June 1956, killing 128 people.
Two years after that, in 1958, two mid-air collisions involving an airliner and a military aircraft led to the creation of the Federal Aviation Authority.
One of those 1958 crashes occurred on May 20, the same day a fatal mid-air collision involving an airliner and a military aircraft happened in Italy as well.
Since the 1956 crash, the U.S. has experienced two mid-air collisions with more fatalities: 134 people were killed near New York City in 1960 and 144 were killed near San Diego in 1978.
The world's worst mid-air collision involved two airliners on international flights, flying above India in 1996. All 349 people aboard the two planes died.
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