The managers in one air traffic control center were unaware of a potential problem, and the manager in the Andrews tower was reluctant to say anything when he noticed that the two planes were two miles closer than FAA standards allow, federal sources said.
Oversight by a manager already is required when the president is on board a White House aircraft.
In a statement Tuesday, the FAA said that “the aircraft were never in any danger.”
The National Transportation Safety Board, which began investigating mistakes by air traffic controllers and pilots last year after error rates spiked, said Wednesday that it will investigate the incident.
An FAA investigation, already underway, is expected to be completed next week.
On Wednesday, the NTSB said it had reviewed 950 cases in the past year when cockpit collision-avoidance systems were triggered, 260 of them worthy of further examination and nine that warranted full investigations.
The worst was an incident last year when, because of a controller’s mistake, a US Airways plane passed within 50 feet of a cargo jet in a cloud bank after taking off from Minneapolis, said Thomas E. Haueter, director of the agency’s Office of Aviation Safety.
“The one in Minneapolis scares the heck out of me,” Haueter said. “That’s the one we lose the most sleep over.”
Ninety people were on board that Philadelphia-bound flight. The cargo plane’s pilot said he never saw the Boeing 737.
Haueter said a near collision in January between an American Airlines Boeing 777 and two C-17 military cargo jets just south of New York also ranked as one of the most serious incidents.
The NTSB, better known for its investigation of plane crashes, intensified its review of nonfatal incidents a year ago to determine whether an apparent increase in the number of errors by air traffic controllers and pilots was evidence of a systemic problem.
They required airlines or pilots to file reports directly to the NTSB whenever collision avoidance systems aboard aircraft went off.
Haueter said the data have not revealed a pattern.
“Usually a problem was caused when somebody made an assumption, like assuming that somebody was going to turn right, and then they didn’t,” he said. “The big issue is that it’s just the first year we’ve been looking into this. It’s probably going to take three to four years to get a better idea of what’s going on.”
On Monday, Obama and Jill Biden, the wife of the vice president, were returning from a television appearance and other events in New York aboard a Boeing 737 that is part of the White House fleet of aircraft.
As the incident unfolded just before 5 p.m., the managers at the Potomac Terminal Radar Approach Control (TRACON) facility in Warrenton were occupied with other duties and unaware that one of their controllers had allowed the first lady’s plane to get two miles closer than allowed by FAA regulations to the wake of a 200-ton C-17, federal sources said.