Spanish air accident investigators are probing an incident last year where two passenger jets, including a Ryanair flight, were just moments from a possible midair collision.
The serious ‘loss of separation’ incident resulted in the two jet’s coming within 100 feet of each other vertically and 2.6 kilometres laterally when they should have been considerably further apart.
While the occurrence is still under investigation, Spain’s Comisión de Investigación de Accidentes e Incidentes de Aviación Civil (CIAIAC) has issued a “provisional information” report regarding the incident.
On October 30th last, Ryanair flight FR-2848 was en route from Shannon Airport to Malaga with 36 passengers and 7 crew on board.
The crew had been in contact with air traffic control in Seville and had been cleared to descend to 15,000 feet at a rate of 2000 feet per minute or more.
Meanwhile, a Vueling flight from Barcelona to Seville, with 153 passengers and 6 crew, was descending towards Seville after being cleared to an altitude of 17,000 feet at a rate of 2000 feet per minute or less.
Both planes routes intersected south west of Cordoba while the minimum required separation between them should have been 1000 feet (305m) vertically and generally 5 nautical miles (9.26 kilometres) laterally.
However, while both aircraft were descending through 22,000 feet, this minimum required separation between the jet’s was lost.
Spain’s CIAIAC has confirmed: “The two aircraft were descending through FL220 (22000 ft) when the separation between the aircraft reduced to 100 feet (30.4 metres) vertically and 1.4 nautical miles (2.6 kilometres) laterally.”
Both jet’s Traffic Collision Avoidance Systems (TCAS) alerted the crews to the imminent danger and issued automatic resolution advisories (RA) to each crew.
TCAS is an onboard system, independent of air traffic control, and warns pilots if another aircraft with the same equipment gets too close and a risk of collision is possible.
The system issues ‘resolution advisories’ that tell the pilot of one or both aircraft to climb, descend or level off in order to avoid conflict or mid-air collision.
According to the investigators both crews initially received TCAS traffic alerts (TA) followed a few seconds later by TCAS resolution advisory (RA).
In this case, according to the interim report: “The conflict was resolved satisfactorily.”
The CIAIAC investigation into the occurrence is continuing and is likely to look at whether the incident resulted from an air traffic control failure or if one or both aircraft crews were at fault.