In the midafternoon of Tuesday, August 4, an air traffic controller in the tower of Reagan National Airport was surprised to find that he had an unexpected intruder into his airspace: the President of the United States. At 2.33 p.m., the helicopter on which he was riding, Marine One, and a lookalike Sikorsky VH-92A Patriot helicopter which serves as a decoy, were suddenly in his airspace, moving from the grassy Ellipse near the White House southward toward the Potomac River.

“National Tower, Marine One, proceeding as briefed,” came the radio call.

The reason this came as a shock is that, by pre-agreed rules, the president’s helicopter was supposed to give the tower three minutes’ warning before it takes off. That’s no mere formality; D.C. is incredibly busy airspace, with commercial jets coming into land on a main runway that’s just three miles south of the White House. Numerous VIP transport, security patrol, and other helicopter flights are constantly threading through an airspace that’s been likened to a spiderweb. Keeping everyone moving without running into each other is a tall order, and the price of failure is tremendous — as attested to by last January’s midair collision between an Army helicopter and a passenger jet that left 67 dead. The three minutes’ notice would have given the tower a chance to halt all other traffic and give the presidential flight clear airspace. But, since no notification had been received, Marine One was now just chugging along right through the middle of everything.

Air traffic controllers are known to ream out misbehaving pilots, especially in busy airspace, but the president’s flight crew don’t get yelled at. “Uh, Marine One, you said, uh, you’re proceeding as briefed?” the tower said, sheepishly. The helicopter’s crew confirmed that it was. “OK,” the tower replied, “no three minutes. Roger. Proceed as briefed.”

Complications ensued. On the tarmac at Ronald Reagan Washington National Airport, an Embraer E175 regional jet operated by Envoy Air was lifting off from Runway 1 on the western shore of the Potomac, bringing it within a mile of Marine One’s flight path along the eastern shore.

FAA rules require aircraft within Reagan National’s airspace to stay at least 1.5 miles apart vertically. The inability to do that resulted in what the agency calls “failure to maintain separation,” a rule violation that requires mandatory........

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