WARRENTON, Va. (AP) — Canadian officials are continuing the investigation into what led two small, private planes to collide in mid-air on Memorial Day in Fauquier County.

Sixty-year-old James M. Duncan of Bethesda, Md., and 57-year-old Paul Gardella Jr. of Burke, Va., were killed when the Beech Bonanza owned by Duncan crashed and burned after colliding with a Piper PA-28 near Warrenton-Fauquier Airport on May 28. The pilot of the second plane, Thomas Proven, of Broad Run was injured but was able to land his 1965 plane at a nearby farm.

The crash is being investigated by the Transportation Safety Board of Canada because Duncan was a doctor with the National Transportation Safety Board and Proven is an inspector with the Federal Aviation Administration. Gardella was a flight instructor and volunteered with the Civil Air Patrol in Washington.

Officials Wednesday said the investigation team is working to determine what caused the crash and how to stop it from happening again.

Both aircraft were certified and maintained in accordance with existing regulations and nothing was found to indicate any airframe failures or system malfunctions. Both pilots and the flight instructor also were certified. And the weather conditions in the area were good at the time of the collision, officials said.

"One of the main areas we haven't answered yet is that, based on the angle of approach and the physical layout of each aircraft, would either pilot have been able to have seen each other," Investigator Jon Lee told The Associated Press.

Lee said the investigative team also is looking at what role air traffic control procedures or software may have played.

Officials hope to have a draft report for interested parties available in late November or early December, Lee said.