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 .
The March 27 incident was publicized days after it occurred . Details released Friday show aircraft were within 100 miles of each other . Incident happened 100 feet over central Florida . Controllers asked pilots to land on small plane unresponsive to radio calls .