What happened
On September 13, 2005, at approximately 11:00 UTC, an Airbus 310 operated by Yes Linhas Aéreas, registration CS-TKI, flying flight YSS 818 from Cancun to Lisbon, experienced a TCAS Resolution Advisory (RA). The aircraft was cruising at FL360 after passing the KOMUT entry point in the Lisbon FIR. Simultaneously, an American Airlines Boeing 767, flight AAL69, was operating on a reciprocal track at the same altitude.
The encounter occurred within the West Sector of the Lisbon ACC in Class C airspace. Although the pilots of both aircraft observed the other and performed maneuvers to maintain lateral separation—specifically, the Boeing 767 turned to the right—the TCAS RA was triggered. The crews chose not to follow the TCAS RA instructions because they believed lateral separation was already being maintained. The incident resulted in no injuries and no damage to the aircraft.
The investigation
The GPIAAF investigation focused on the coordination between the Santa Maria OCA and the Lisbon ACC. It was established that the Airbus 310 had requested a route change from its original flight plan (which used GUNTI as an entry point) to enter the Lisbon FIR via KOMUT. While Santa Maria coordinated this change, the automated OLDI message containing this update was rejected by the Lisbon Flight Data Service (SDV) because of a discrepancy with the existing flight plan.
Investigators found that the SDV operator and supervisor did not process the rejected message according to standing instructions, allegedly because they believed they had received verbal orders to ignore such messages during system testing. Furthermore, the Lisbon West Sector controller was unaware of recent service instructions (effective since May 2005) regarding new automated coordination procedures with Santa Maria. Consequently, the controller did not realize the Airbus 310 was now entering via KOMUT. Meanwhile, the Santa Maria controller authorized the Boeing 767 to climb to FL360 via the same KOMUT point, unaware of the conflicting traffic.