Incident Overview
On 19 July 2015, an incident occurred in the FIR Warszawa, southwest of the KOTEK point, involving a Boeing 737 (call sign SAS7442) operated by Scandinavian Airlines and a Boeing 777 (call sign AUA52) operated by Austrian Airlines. The required separation minima were 7 NM horizontally or 1,000 ft vertically, but the actual minimum distance between the two aircraft was 5 NM and 600 ft.
Sequence of Events
A controller in the ACC GAT sector "J" with OJTI instructor privileges took over the operational position and, according to his statement, disabled the MTCD warning system for training purposes. Shortly thereafter, SAS7442, flying along the LENOV–MOTAD route, reported deviating around thunderstorms with a heading of 340° at flight level FL360. The controller identified the aircraft on radar and cleared it for own navigation to KOLOB point after passing the storms.
Five minutes later, AUA52, flying along the GORAT–TUSIN route at FL360, contacted the controller. Shortly after, SAS7442 reported a heading of 330° after avoiding thunderstorms and turning toward KOLOB. Six minutes later, an STCA yellow alert was generated on the radar display. The controller then instructed AUA52 to immediately descend to FL350. The pilot acknowledged and began the descent, but due to the aircraft's mass, the response was not immediate.
The controller then informed SAS7442 of the traffic (AUA52), and an STCA red alert appeared. The crew of AUA52 reported visual contact with SAS7442 and crossing FL355, approaching FL350. The closest proximity between the two aircraft was 5 NM and 600 ft.
Causes
The investigation identified two causes: 1. The ACC GAT controller did not notice the convergence of the two aircraft while waiting for the passage of two other aircraft (AZA493 and THY1YL). 2. The controller did not issue a climb instruction for SAS7442 simultaneously with the descent instruction for AUA52.
Contributing Factors
Contributing circumstances included the controller's disabling of the MTCD warning system and probable fatigue resulting from working a fourth consecutive shift after three days off, as well as operating at the upper limits of sector capacity.
Aftermath
No recommendations or preventive actions were issued by the investigating body.