Incident Overview
On Wednesday, 18 October 2017, at 13:50 UTC, a Boeing 737-800, registration EI-FJJ, operated by Norwegian Air International as flight IBK1CH, was en route from Oslo to Alicante. Two flight attendants located at the rear of the aircraft were injured during the flight. The aircraft carried 6 crew and 178 passengers; one flight attendant sustained serious injuries and one minor injuries; all passengers were uninjured.
Flight History
The aircraft took off from Oslo at 10:32:21 UTC and climbed to FL370. Toward the end of the cruise, it entered Barcelona ACC airspace via ANETO. The planned route was to descend southerly over Valencia, but due to bad weather throughout the east and northeast of the Iberian Peninsula, the crew requested a route change, which ATC authorized. At 13:38:37, the aircraft began a descent at approximately -1700 fpm, initially heading 200°, then turning to 163°.
Weather and Conflict
The area was affected by a phenomenon called convective training. At 13:50:21, the aircraft, at 20,075 ft descending to a selected altitude of FL190, triggered a conflict alert as it approached another aircraft that had been instructed to hold. The conflict was identified by both ATC's short-term conflict alert system (STCA) and the on-board Traffic Collision Avoidance System (TCAS), which issued resolution advisories (RAs) for avoidance maneuvers.
TCAS Maneuver and Injuries
During execution of the TCAS avoidance maneuvers, the aircraft recorded swings in vertical acceleration that were consistent with the general convective activity in the area. These swings caused flight attendants 2 and 3 to fall, resulting in the injuries detected afterward.
Investigation Findings
The investigation determined that the failure of controllers in two adjacent sectors to plan and coordinate led to the conflict alert. While maneuvering to clear the alert, the aircraft entered an area of turbulence. No safety recommendations were issued.