What happened
On November 19, 2012, at approximately 05:15 UTC, a Boeing 767-300, registration I-NDMJ, was operating a commercial flight from Havana, Cuba, to Milan Malpensa, Italy. The flight, which was conducting a line training session with a pilot in command (PIC) occupying the jump seat, was cruising at FL350 when it encountered an area of severe turbulence approximately 100 nautical miles west of the BALTN waypoint.
At the time of the encounter, the seatbelt sign was off, and cabin crew were performing meal services. The sudden turbulence caused abrupt changes in the aircraft's attitude, altitude, and airspeed. The flight data recorder captured a 35-second period of instability, including vertical speeds of up to +6,100 ft/min and pitch oscillations ranging from -2.5° to +12.7°.
As a result of the violent motion, several passengers who were not seated or buckled in, along with cabin crew members, sustained injuries. Specifically, the event resulted in 1 serious injury and 34 minor injuries among passengers, as well as 1 serious injury and 2 minor injuries among the crew. The turbulence also caused damage to the aircraft interior, particularly in the rear of the passenger cabin, where catering trolleys were displaced.
Following the event, the flight crew stabilized the aircraft and assessed the situation. Given that the aircraft's airworthiness was not compromised, the medical status of the passengers was stable, and a diversion to the planned alternate airport (KMIA) would have required flying back through the turbulence area, the crew decided to proceed to Milan.
The investigation
The ANSV conducted a safety investigation to determine the cause of the turbulence and the resulting injuries. Investigators reviewed flight planning documents, meteorological reports, and flight data recorder information.
Analysis of the flight data confirmed that while the G-loads remained within the aircraft's structural limits, the vertical accelerations were significant. The investigation also examined weather documentation, including SIGMETs and satellite imagery. It was noted that the crew had utilized the onboard weather radar in WX Radar-MAP mode, but the turbulence was not detectable via this method due to the lack of convective clouds at the flight level.
Findings
- The primary cause of the incident was the encounter with severe clear-air turbulence (CAT) that was unpredictable by the crew.
- The turbulence was not reported by other aircraft in the area, nor was it identified in any SIGMETs.
- The encounter likely occurred due to the aircraft passing through a jetstream.
- The injuries were caused by the fact that several passengers and crew members were not restrained by seatbelts at the moment the turbulence hit.
- The turbulence was undetectable by the onboard weather radar because it occurred in clear air without detectable convective moisture.