What happened
On April 4, 2010, an Aer Lingus Airbus A320, registration EI-DEK, was operating a passenger flight from Tenerife (GCTS) to Belfast (EGAA). The aircraft had previously received an oceanic clearance via datalink for FL360.
As the aircraft approached the NAVIX transition point between the Lisbon and Santa Maria oceanic control areas, the Santa Maria oceanic controller contacted the Madeira sector controller of Lisbon ACC to request a flight level change to FL370 to avoid potential conflict with another aircraft. The Madeira controller accepted the proposal and instructed the aircraft to climb to FL3/370.
However, a communication gap occurred during the update process. While the change was being coordinated via telephone, the updated information was not recorded in a shared system or transmitted via datalink. When the pilot contacted the Santa Maria radio operator to confirm the new clearance, the operator—unaware of the recent change—reiterated the original FL360 clearance.
Faced with conflicting instructions, the pilot began descending to FL360 to ensure compliance with the original oceanic clearance but then decided to enter a holding pattern at NAVIX to wait for clarification. During this maneuvering, the aircraft experienced a TCAS/TA (Traffic Advisory) involving another aircraft, MEDIC-01, which was crossing the flight path 1,000 feet below.