One week after a control-tower mistake at Reagan National Airport sent passenger planes hurtling at one another at a combined speed of 436 miles an hour, the government temporarily banned aircraft from flying in opposite directions as they arrive and depart from airports.

The nationwide prohibition on two-way traffic would not have prevented the July 31 incident in which a controller sent two commuter flights into the path of a third commuter jet that was inbound. There were 192 passengers and crew members aboard the three planes.

David Grizzle, chief operating officer at the Federal Aviation Administration, said in a memo Tuesday that preliminary findings of an investigation confirmed that a communication lapse between the tower and a radar control facility in Warrenton was to blame.

“This incident should not have happened,” Grizzle said in a memo to Michael P. Huerta, the acting FAA administrator.

When a storm-driven wind shift occurred, supervisors in the tower and in Warrenton agreed to turn traffic at National 180 degrees so inbound planes would approach from the north rather than from the south. That meant outbound planes should switch their takeoffs to the south.

On a busy Tuesday afternoon, that change was not communicated to at least one controller in the tower. Unaware, she sent the two outbound planes off to the north.U.S. Transportation Secretary Ray LaHood declined to specify what caused the communication failure Tuesday, citing the ongoing investigation. The suggestion of a possible cause emerged from Grizzle’s memo.

“This incident also raised the issue that front line managers are not only overseeing operations in the tower, but also managing administrative tasks,” Grizzle said. “During times of moderate to heavy and/or complex traffic, we need to be sure that they are solely focused on operations at the facility.”

LaHood and the FAA have a history of swift reaction when issues arise. Several controllers were suspended or fired last year after a report that one had been sleeping during an overnight shift at National led to discovery of other late-night nappers.

Grizzle said the suspension of two-way traffic was being taken “out of an abundance of caution” while improvements in oversight and training are considered.

Two-way traffic, or “opposite direction” operation, as the FAA calls it, is when aircraft arrive or depart opposite to the predominant flow of traffic on that runway based on the wind direction.

This is a common event, and there are many reasons that opposite-direction traffic may be used. They include protecting noise-sensitive areas, conducting flight checks of navigational systems and expediting the landing of emergency or VIP aircraft. Pilots will also ask for opposite-direction operation for convenience. It is up to the controller to approve the request, traffic permitting.

The tower controller in last week’s incident discovered she had directed two planes to take off in the path of the incoming plane after they already were airborne. Tower controllers own the airspace roughly three miles from the end of the runway.

The inbound pilot had been turned by the Warrenton controllers about 10 miles out and was put on an established flight path that follows twists of the Potomac south to minimize engine noise. He was instructed to switch radio frequencies to contact the tower.

There is no rigid definition to how quickly he should have done that, largely because at busy hours a pilot might have to wait until that frequency clears to make the contact. When the inbound pilot called the tower, the controller sounded surprised.

“Are you with me?” she is heard saying on a recording of the radio transmission.

Recognizing the problem, the controller ordered the pilot to turn to the right.

The controller ordered an additional right turn, then instructed the pilot to abort his approach.

As the pilot executed the maneuver, his plane was little more than eight-tenths of a nautical mile from the oncoming plane, or about 1,650 yards, and the difference in their altitude was 800 feet. With a combined speed of 436 mph, at one point they were 12 seconds apart.

As he turned to avoid contact with the first plane, the inbound pilot came too close to the second plane: 800 feet of altitude. Planes are required to maintain a separation of three miles and 1,000 feet of altitude.

Grizzle said investigators also have resolved one issue stemming from the incident that had raised concerns.

The inbound pilot who had been redirected twice is heard on the radio cautioning the controller that his plane is low on fuel. Grizzle said the investigation revealed that the plane, inbound from Portland, Maine, with 73 on board, “did have adequate fuel, and, in fact, had more fuel than the FAA regulations require.”