Washington (CNN) -- Acting at the request of an air traffic controller, the pilot of a Southwest Airlines B-737 pulled within one-tenth of a mile of a small, four-seat aircraft last month to check on pilot of the smaller plane, who had not responded to radio calls, the National Transportation Safety Board said Friday.
The March 27 incident was publicized days after it happened, when Federal Aviation Administrator Randy Babbitt suspended the air traffic controller, for "compromising the safety" of the planes' occupants. But the details released Friday for the first time show just how close the two planes came.
According to the NTSB, the planes came within 0.1 miles of each other, far closer then the required separation of three miles. They also were separated by 100 feet in altitude, less than the 1,000 feet required, the NTSB reported.
The incident happened 11,000 feet over central Florida, when controllers at the Central Florida TRACON, a regional radar facility, were unsuccessful in contacting the pilot of the Cirrus SR22, which was en route to Kissimmee, Florida. The plane had been out of radio contact with the Jacksonville Center for more than an hour.
A TRACON controller sought the assistance of Southwest Airlines flight 821, which was then 10 miles from the smaller aircraft, asking the Southwest pilot "to attempt to verify the condition of the occupants" of the Cirrus, the NTSB said. The Southwest pilot "obliged," and controllers guided the jetliner towards the unresponsive plane. A separate radar scope was set up and a single frequency was used by a front-line manager who provided instructions to the Southwest jet.
When the Southwest jet was about five miles from the smaller plane, the pilot reported seeing the plane visually and on a collision avoidance system. The jet "maneuvered on his own alongside of" the smaller plane, the NTSB said.
The crew reported seeing "two occupants in the Cirrus and no apparent movement from them" before being vectored away to its Orlando destination.
The FAA said both planes landed safely. Southwest Airlines reported in March that it had suspended the pilot of the jetliner pending an investigation.
Both the FAA and NTSB are investigating. Neither has issued any findings or conclusions.
Aviation authorities say the protocol for intercepting unresponsive aircraft is to scramble military jets.
"By placing this passenger aircraft in close proximity to another plane, the air traffic controller compromised the safety of everyone involved," FAA Administrator Randy Babbitt said in a statement in March.
"This incident was totally inappropriate." "We are reviewing the air traffic procedures used here and making sure everyone understands the protocols for contacting unresponsive aircraft," Babbitt said.
Southwest Airlines said the flight had 137 passengers and a crew of five.