Incident Overview
On approach to the SWAPP intersection, a Braniff Boeing 727 and a United Boeing 727 were operating at their proper assigned altitude of 35,000 feet on converging jetways. The air traffic controller was in the process of issuing radar vectors to ensure proper lateral separation when the control frequency became blocked. Attempts to override the blocked frequency were unsuccessful. As a result, the two aircraft passed with approximately 200 feet of vertical separation and zero horizontal separation. The flight crews did not see the other aircraft until the near collision occurred.
Communications
Immediately following the incident, the Braniff captain's initial transmission cleared the frequency, and all communications returned to normal. The Braniff crew was not aware of the frequency problem that had occurred.
Flight Data
The flight data recorder (FDR) on the Braniff 727 indicated a solid 5-minute event marker for microphone activation that correlated with the time of the incident. Subsequent bench tests performed on the equipment installed in the Braniff aircraft revealed no discrepancies.
Investigation Findings
The investigation did not determine a specific cause for the communication blockage. No probable cause was stated in the report.