What happened
On November 9, 2017, a Boeing 737-800 operating as flight ENT7361 was descending through FL179 within the TMA Grand Canaria (GCLP). The flight was following the SAMAR5C arrival procedure, which requires vectoring due to signal limitations at the GDV DVOR/DME below FL150. The air traffic controller (KRL APP) instructed the crew to descend to 6,000 feet and, upon reaching the GDV waypoint, to intercept the 160-degree radial.
During this period, another aircraft, TVP7311, was departing GCLP and climbing to 3,000 feet. While communicating on the same frequency, the crew of ENT7361 mistakenly intercepted a heading instruction that was actually directed at another aircraft, ENT5073. The controller had instructed ENT5073 to change course for an approach to GCLP.
As ENT7361 passed waypoint TODKO, the controller observed the crew initiating a left turn. The controller subsequently instructed the crew to return to the GDV waypoint. Due to a lack of immediate confirmation from the crew, the controller issued a climbing restriction of 7,000 feet for TVP7311 and a descending restriction of 9,000 feet for ENT7361 to maintain separation. Eventually, the separation between the two aircraft was reduced to a horizontal distance of 5.9 NM and a vertical distance of 5,100 feet.
The investigation
The investigation, conducted by the operator's internal commission, examined the radio communications and the sequence of flight path deviations. The investigation focused on the simultaneous presence of two aircraft with similar callsigns on the same frequency and the specific moment the incorrect instruction was accepted by the crew of ENT7361.