Two jet airliners converging almost head-on missed colliding over North Carolina Sunday by less than 1 1/2 miles, and a new emergency device in one of the planes, designed to warn of collision threats, failed to alert the pilots.
It was a close brush with disaster, one that involved a freakish combination of breakdowns and mistakes. Those included temporary clearance by controllers for one plane to use an unorthodox though legal altitude and assorted problems with radio transmissions to and from both planes.
The airliners, a Continental Airlines Boeing 727 and a USAir McDonnell Douglas DC-9, carried a total of 194 passengers and crew.
The close call was regarded as particularly disturbing because so many things went wrong in a tighttime frame and because no automatic last-resort warning was given by the new anti-collision system on which such great hopes have been placed.
Even more unnerving was that the co-pilot of the DC-9 estimated the distance between the planes as a quarter-mile or less. But even at the 1.45-mile distance calculated by the Federal Aviation Administration from its radar computer tapes, the anti-collision system should have given the alarm.
All the nation's 4,000 or more large airliners must have such systems installed by the end of 1993. About 800 are already in service.
The DC-9 had the system; the 727 did not. But the device can do its job in one plane if the other has only the conventional altitude-reporting transponder required on all airliners.
Les Baines of Bendix-King, builder of the system on the DC-9, agreed with the aviation agency that a warning should have been given if the system was working. "We're trying to find out what happened ourselves," he said.
The National Transportation Safety Board asked the aviation agency on Tuesday for all the data it had on the incident.
The DC-9, USAir Flight 1467, was flying south-southeast at 33,000 feet from Pittsburgh to Myrtle Beach, S.C. The 727, Continental Airlines Flight 387, was heading north-northeast at the same altitude from Jacksonville, Fla., to Newark, N.J.
According to official accounts and interviews with several people close to the inquiry, what had been a routine handling of air traffic turned suddenly into a few minutes' nightmare shortly before 9:30 a.m. The planes had been turned over for traf
fic guidance to controllers in the Washington air-traffic center at Leesburg, Va., about 45 miles west of the capital.
The first important thing that happened was a phone exchange between two Washington controllers -- a trainee responsible for the airspace where the USAir plane was flying and a full-fledged controller responsible for the sector just to the south, known as Raleigh High.
The trainee, being monitored by a full-fledged controller looking over his shoulder, asked the Raleigh High controller if he could accept the DC-9 at 33,000 feet, even though the preferred altitudes for southbound planes were 31,000 and 35,000. There was a temporary conflict with other planes at those altitudes.
The Raleigh High controller agreed, on the condition that a third plane, headed west at 31,000 feet,would be quickly guided out of the way and that the DC-9 could promptly be sent down to the vacated altitude from 33,000 feet. But when the trainee told the crew to switch radio frequencies and contact the other controller, he gave them a frequency that had been changed the week before.
The instructor immediately caught the error but could not regain contact with the crew because they had already switched. But a Washington controller handling still a third sector of airspace got the radio call from the plane and told the crew the proper frequency.
Then came the second breakdown. The USAir crew had evidently not only switched frequencies but had switched to a companion radio set. They could not make contact with the controller responsible for the more southerly air sector.