The two planes collided at a place local pilots call the training ground, a comfortable expanse of open air unbroken by the flight paths that carry big jetliners into the region's busy airports.
The aircraft tumbled to the Virginia countryside Memorial Day afternoon, one breaking into pieces as it landed in a field, the other bursting into flames among trees.
How do three trained pilots on two small planes manage to collide on a sunny afternoon?
Pilots say that it doesn't happen often but that it takes only a split second to make a fatal error.
Speed, blind spots and distractions in the cockpit can combine to put planes too close and, in Monday's case, result in a collision that left two men dead and another hospitalized.
Although investigators are just beginning their work, distractions inside the two cockpits might prove to have been a factor.
One pilot had just switched away from the radio frequency that the other pilot almost certainly was using. The second pilot was working with a veteran flight instructor who was evaluating his skills for a required review.
"If he was doing an evaluation, maybe they were both 1/8focused 3/8 inside the cockpit, trying to teach or learn something specific, practicing something, programming the GPS, programming the radio," said Lt. Col. Paul S. Cianciolo of the Civil Air Patrol. "There's a whole bunch of things that can go on inside the cockpit."
The three pilots had remarkable credentials.
The survivor, Thomas R. Proven, 70, of Broad Run, Va., is an investigator for the Federal Aviation Administration.
James "Mike" Duncan, 60, of Bethesda, Md., was a doctor and chief medical officer for the National Transportation Safety Board.
Paul Gardella Jr., 57, of Burke, Va., was a professional flight instructor and the region's chief examining officer for the Civil Air Patrol.
A hot haze had settled over Virginia by mid-afternoon Monday when Gardella and Duncan took off from Warrenton-Fauquier Airport in Duncan's Beechcraft BE-35 and turned south toward the training ground for a flight review required of pilots every two years.
"There's one hour flying in the air, and you can work on anything that the instructor and student agree they want to work on," said Dave Fields, who learned to fly under Gardella's patient eye and keeps a plane at Warrenton.
The training ground is popular, because it's outside the airspace that's controlled by air traffic controllers. Pilots communicate directly with one another but are not required to maintain contact with federal air traffic controllers.
"It's just much easier to maneuver without having to deal with" air traffic control, said Tom Haueter, who heads the NTSB Office of Aviation Safety and keeps his private plane at the Warrenton airport.
Because neither plane was being tracked, it will take weeks to determine how they came to cross paths. Investigators are examining the flight paths of all the untracked aircraft in that area to identify the nexus where two of the planes dropped from the radar screen. Once they know that, they will backtrack to re-create the fatal encounter.
"We have captured that data, but we haven't had a chance to review it," said Jon Lee of the Transportation Safety Board of Canada.
The Canadians were asked to lead the investigation because it involves employees of both U.S. agencies - the FAA and the NTSB - that usually probe crashes.
Lee said they also have a Global Positioning System device from Proven's Piper PA-28.
"There's good information on both aircraft," he said.
Pilots agree that sun glare can cause problems and that blind spots do, as well.
"Sometimes, the sun angle blocks your view; sometimes the wing blocks your angle," Haueter said.
Robert Sumwalt, an NTSB board member and former airline pilot, said that unlike a one-dimensional crash between two vehicles on the ground, planes can come at each other at high speed from an infinite number of angles.
"When you're four seconds away from a head-on collision, the other plane still just looks like a tiny speck," he said. "I don't think pilots spend enough time looking outside the cockpit. Pilots have a lot of instruments to look at inside."
Cianciolo, a former Air Force flier, said, "You have more blind spots above you and behind you. They were operating on visual flight rules, so it's basically just looking out the window and knowing from other reports what other aircraft are in the area. Someone wasn't paying attention."
Just before the impact, Proven apparently reached for his radio to contact air traffic control. That meant switching from the frequency pilots use in the training grounds to one used by air traffic control. A controller in Warrenton responded and was about to locate the plane's radar beacon when the planes collided.
"I haven't listened to any of the audio to confirm that or even analyze what the situation was there yet," Lee said. "The FAA has made us aware that those particular audio tapes will be of interest to us."
Whether Gardella and Duncan saw Proven's plane before the impact sheered their six-passenger aircraft in half will never be known. The wings, engine and cabin plunged into a clump of trees. The plane's tail landed more than a half-mile away.
Proven guided his crippled plane between two stands of cedar trees and was able to land in a field before one cedar snapped off one wing. He staggered, bleeding, from the plane to seek help. He was released from the hospital Wednesday but was not giving interviews.
When small planes go down, phones begin ringing.
Mike Truschel, a stunt pilot with the Flying Circus Air Show in Warrenton, got the call and began a round of calls to make sure the victims weren't show pilots.
Dave Fields had been by the airport that morning, but when his phone rang he was sitting by a friend's pool.
"I heard the name of the man who survived, but they didn't know who had died," Fields said. "The next morning, I called the airport, and they confirmed it was Paul. I just drove out to the airport to be with the people there. He was a great pilot."