At a towered, radar airport, like most big commercial ones, the controller can follow on the screen where aircraft are, where they're headed, and how far apart they are. At a non-towered, uncontrolled airport, like Gaithersburg KGAI, where my plane is usually based, pilots rely entirely on the "see and avoid" policy to stay out of one another's way, and on position announcements on the CB-style local frequency. (For instance, "Cirrus XXX is 7 miles to the north, entering right downwind for runway 32." "Mooney YYY is on the right downwind for 32, abeam the numbers and about to turn base." "Piper ZZZ is taking off from 32, departing VFR to the north.")

At this towered, but non-radar, airport at FDK, the controller was clearing aircraft, as you can hear in a very upsetting Live ATC recording. But she could not see all of them, nor did they see each other.

3) Last month Alan Klapmeier, who with his brother Dale founded the Cirrus Design company in the 1990s, was formally inducted into the Aviation Hall of Fame. Their achievement was to design and produce the Cirrus aircraft line, which are made in Duluth, Minnesota and are now the most successful planes of their kind worldwide.

Thirty years ago, when Alan was a young pilot, he was in a mid-air crash in the Midwest. He barely managed to bring his plane safely to the ground. He resolved that when he ran his own airplane-making company—he was such an entrepreneur that he thought of it as when, not if—he would protect pilots against this danger by equipping entire airplanes (not just passengers) with parachutes. That is what Cirrus did, with its SR-20 and SR-22 aircraft. The Cirrus pilot's split-second decision to deploy the parachute appears to have saved that plane's occupants, while tragically the helicopter was destroyed on impact after falling 1000 feet to the ground.

4) Frederick has an active mix of traffic. I have often watched for glider-tow planes taking off, or gliders landing, while myself preparing to land there. It has an active helicopter school, plus both slower (propeller plane) and faster (jet) airplane activity.

So dealing with traffic-roundabout-type interactions is fairly normal for pilots there and at many other airports. Usually the main separation between airplanes and helicopters is a matter of altitude. The "traffic pattern" for airplanes as they prepare to land typically begins at around 1000 feet above the ground. Helicopters usually operate much lower. For some reason, in this case the airplane (which had been told by the controller to maintain its altitude) and the helicopter were at the same place at the same time.

Below, a number of reference materials. I am including a transcript of the Live ATC recording but not a link, because the recording is more disturbing than instructional (and appears to include the voices of people in the helicopter as it went down.) I am also not including a link to the local newscast I'm hearing just now, which says that "miraculously" the plane was relatively undamaged when it came to the ground. The "miracle" was the parachute. Update: The Washington Post has a good story with additional details here. Update-update: You can hear a press statement from the company that operated the helicopter, here; it includes a discussion of the difference the parachute made.