What happened
On May 25, 2017, at approximately 15:00, a serious near-collision occurred in the airspace northwest of Arvidsjaur, Sweden, during the international military exercise ACE 17. The incident involved two separate flight groups from the "blue" force: a Swedish Gripen group (HAMMER) and a French Mirage 2000 group (GUSTO).
The Swedish Gripen aircraft were performing administrative flight maneuvers, returning to their home base. Simultaneously, the French Mirage 2000 aircraft were transitioning from an air-to-air refueling area toward their combat area. During this transition, the passage between the two aircraft was uncontrolled, creating an immediate risk of collision.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the event by reviewing recorded position data from D-ACMI 2, audio recordings from combat control and the Gripen's registration system, and various exercise planning documents. The investigation also included interviews with the pilots, supervisors, and the combat control (STRIL) and exercise leadership teams.
Investigators analyzed the operational risk management (ORM) methods used, the workload of the Mission Commander, and the specific separation procedures established for the exercise. The investigation also looked into discrepancies between the digital maps used by the different flight groups.
Findings
- The exercise leadership underestimated the risks of separation violations during the administrative flight phases of the exercise.
- There were no established separation procedures in the Airspace Control Order (ACO) for transitions between the air-to-air refueling area and the combat area, or for transitions from the combat area to transit corridors.
- The Mission Commander faced a high workload due to the complexity of the planning and the daily updates required for the ACO and ATO.
- Digital maps used by the HAMMER and GUSTO groups displayed conflicting information; for example, the Gripen group's map lacked information regarding refueling areas, while the Mirage 2000 group's map showed a route through an area not defined as a transit corridor.
- The pilot of the Mirage 2000 changed altitude based solely on their own situational awareness without receiving clear confirmation from combat control, a move permitted under the visual flight rules in effect at the time.
- The definition of "situational awareness" (SA) within the ELEVATOR altitude change procedure was not sufficiently clear, leading to differing interpretations among the crews.