What happened
On January 20, 2005, an Air Europa Boeing 767-300, registration EC-HPU, was operating a scheduled international passenger flight from Santo Domingo to Madrid. While cruising at FL330 over the Atlantic Ocean, the aircraft entered an area of severe turbulence near a known jet stream and a developing storm front.
At approximately 03:26 UTC, the aircraft began to experience significant vertical accelerations. The flight crew had previously noted the possibility of a cold front and embedded cumulonimbus clouds in the area. As the aircraft encountered the turbulence, it experienced a sudden increase in vertical acceleration, reaching a peak of 2.081 g. This was accompanied by an abrupt climb of approximately 2,800 feet in just 36 seconds and multiple overspeed warnings as the Mach number reached 0.874.
During the event, the aircraft's pitch angle fluctuated significantly. The sudden movements caused several cabin crew members, who were in the process of clearing meal trays, to be thrown against the ceiling and floor. One flight attendant suffered a fractured tibia and fibula, while three other crew members and one passenger sustained various injuries. Despite the turbulence, the crew managed to stabilize the aircraft, eventually returning to the original flight level and continuing the flight to Madrid, where they landed without further incident.
The investigation
The CIAIAC examined flight data recorder (FDR) and cockpit voice recorder (CVR) information, as well as meteorological charts and operational manuals. The investigation focused on the aircraft's approach to the jet stream and the effectiveness of the crew's response to the changing weather conditions. Investigators analyzed the fluctuations in static air temperature (SAT) and wind speeds, noting that a drop in temperature had occurred shortly before the encounter, which could have signaled the approach of the jet stream and associated clear air turbulence (CAT).
Findings
- The primary cause of the accident was an unexpected encounter with severe turbulence in the vicinity of a jet stream and a developing mass of storm clouds.
- The turbulence led to rapid, large-scale changes in altitude and significant vertical acceleration.
- While the crew had identified the storm front, the suddenness of the encounter prevented them from reducing the airspeed to the manufacturer-recommended turbulence penetration speed.
- The aircraft's autopilot attempted to maintain airspeed, but the extreme vertical forces caused the aircraft to climb and descend abruptly.
- The investigation noted that monitoring changes in outside air temperature (OAT) and wind could have potentially helped anticipate the onset of the turbulence.
Safety action
Following the investigation, the CIAIAC issued a recommendation to the operator to provide transatlantic flight crews with detailed training materials to assist in anticipating jet stream-related clear air turbulence by monitoring static air temperature and associated wind variations.