The eight-seat recreational airplane, a single-engine Gippsland Airvan, is cruising peacefully over southern Maryland on a hazy June afternoon, pilot and passengers enjoying the view from 4,000 feet, where the Nanticoke River runs into the swamplands at the edge of the Chesapeake Bay. Suddenly—whoosh! A trademark shape most of us encounter only in the movies or at airshows darts underneath the 100-knot pleasure craft, then carves a semi-circle in the sky in front of it. A voice crackles in the pilot’s headset: “This is a United States Air Force armed F-16. You are in violation of restricted airspace. Do you require any assistance?”

No response from the Airvan. A minute or two later, the fighter is back, aiming for a more dramatic impression. It executes the “head butt,” soaring up vertically within 500 feet of the intruder’s nose. The voice in the earphones sounds less helpful this time: “This is a United States Air Force armed F-16. You have been intercepted. Please acknowledge or rock your wings.”

The jet and an unseen wingman have scrambled from Andrews Air Force Base, just east of Washington, D.C. But their controllers sit 400 miles north, outside the faded Erie Canal town of Rome, New York, amid a forest of glowing monitors at the headquarters of the Eastern Air Defense Sector (EADS). Yellow blips track every aircraft aloft east of the Missis­sippi River, several thousand on a typical weekday afternoon like this.

A general aviation airplane without a flight plan, chugging into restricted airspace, does not take long to stick out from the herd. If the Airvan continues to ignore the fighters in its face, EADS will pass an alert up a chain of command, where unspecified persons will have to decide what to do about it, perhaps within minutes, if the off-course pilot swings west toward the nation’s capital.

This particular interception turns out to be a dress rehearsal. The Airvan’s pilot and copilot are Bill Parris and Michael Regen, two Civil Air Patrol volunteers on a day off from their real jobs, as radio station owner and restaurant supply wholesaler. The routine is choreographed in advance with the Andrews top guns. “Nice work, braves,” Parris compliments the F-16 pilots as the passenger airplane peels off toward its home hangar, at Martin State Airport near Baltimore.

This was practice, but the real thing happens often enough. One of the few detailed studies on the subject, a 2005 Government Accountability Office (GAO) report, found 3,400 violations of restricted airspace, or about three a day, in the 39 months following the September 11, 2001 terrorist attacks, which rewrote the rules of U.S. aviation. About 88 percent of the offenders were general aviation pilots, and seven percent were military. The most common reasons for infractions were pilots altering flight plans to avoid bad weather, or not keeping up to date on the shifts and expansions of the government’s no-fly zones. The zones can change with little warning, as when the president travels. Nearly half the violations—43 percent— tallied by the GAO were in the Washington, D.C. area.

Most violators, of course, respond to a radio warning from Federal Aviation Administration controllers, and if not to that, then to the bright red and green lights used to flood the cockpit of intruders in the vicinity of Washington, and if not that, then to the Coast Guard Dolphin helicopters that sometimes precede the jet fighters. All the same, military aircraft have engaged interlopers “hundreds of times” over American skies since 9/11, says Davi D’Agostino, the GAO’s director of Defense Capabilities and Management. And defenders cite at least three cases last year alone when they feared they would be ordered to apply the ultimate sanction: annihilating a general aviation aircraft to stop it from committing a presumed terrorist act.

On April 6, 2009, what turned out to be a mentally disturbed young Canadian pilot entered U.S. airspace over Lake Superior without warning, and led Air National Guard F-16s on a five-hour chase over four states before finally landing on a country road in Missouri. Minnesota Air National Guard pilots were the first to intercept the Cessna 172 near Michigan’s Upper Peninsula. National Guard units from Wisconsin and Louisiana took over as the pilot continued south without responding to the military jets.

Failing to raise the off-course Cessna 172 on the radio, the F-16s tried to get the pilot’s attention: firing flares in front of the renegade aircraft and flashing their landing lights. When the Cessna came within five miles of downtown Madison, the governor, on the recommendation of the Wisconsin homeland security advisor, ordered the state capitol building evacuated.

The Missouri state troopers who arrested Adam Leon reported he was trying to commit suicide. “If he had turned toward Chicago, he would have gotten his wish,” says Gary Miller of the Federal Aviation Administration’s Office of Tactical Operations Security, who monitored the slow chase. “That’s the closest we’ve ever come to shooting down somebody on my watch.”

Just 18 days later, Maine retiree William Wales, flying down to see his daughter in North Carolina, strayed over Washington, D.C.’s restricted zone. Though repeatedly hailed on emergency frequencies by F-16s, he failed to respond, prompting a lock-down at the White House, preparations to evacuate the Capitol, and frayed nerves at EADS, whose staff flagged the incident to the North American Aerospace Defense Command (NORAD) in Colorado and braced for an order to fire. “Everything looked to be going against this man for a while,” says Air Force Master Sergeant Michael Roberts, who was directing the interceptors from his chair in Rome that day. Wales finally saved himself when a Coast Guard helicopter flew by with a light board, a sort of neon sign, ordering him to call a certain radio frequency. He did, and was escorted to an airstrip out of harm’s way.

Last September, NORAD sent F-16s after a Mooney M20M that lost contact with controllers over Michigan and subsequently crashed near Muncie, Indiana. Military officials reported that the hobby pilot was apparently unconscious in his cockpit. He died in the crash.