Two passenger aircraft entered Irish controlled airspace near Reporting Point BANBA at high level off the South East coast of Ireland. One was an MD-83 routing northwards towards Dublin from Faro, and the second was a B737 routing westwards towards Cork from Stansted. The former was maintaining Flight Level (FL) 280, while the latter, which was cruising at FL300, was cleared initially by the Shannon based Air Traffic Control (ATC) Radar Controller to descend to FL290 and subsequently to FL100. This ATC clearance conflicted with the path of the northern bound aircraft, and, in spite of at least four warnings, one verbal and three electronic, the Radar Controller appeared not to comprehend the closing speeds of the two aircraft and allowed the higher one to descend and lose the required minimum vertical and lateral separation from the other. What ensued was a critical failure of the human element of the ATC system to rectify this situation.
The last resort safety net in this extreme circumstance, each aircraft’s on board Traffic Alert and Collision Avoidance System (TCAS), automatically activated with a commanded warning to each aircraft. The pilot of each aircraft reacted correctly to this TCAS warning, one climbed his aircraft as instructed by the system and the other descended his aircraft as instructed by the system. A potential mid-air collision was thus narrowly avoided due to the TCAS activation and the correct response of the pilots. With separation subsequently re-established by ATC, both aircraft continued onwards and landed at their respective destinations.
The Air Accident Investigation Unit (AAIU) of the Department of Transport was notified of this Serious Incident shortly after it occurred. Three Safety Recommendations are made as a result of this Investigation.