What happened
On September 2, 2013, at 02:54 UTC, an Airbus A330-203, registration PT-MVL, was operating a commercial flight from Madrid, Spain (LEMD) to São Paulo, Brazil (SBGR). While cruising at FL400 over the Atlantic Ocean near the NANIK waypoint, the aircraft suddenly entered an area of severe turbulence. The encounter was accompanied by the presence of St. Elmo's fire and noises resembling hail.
During the period of instability, which lasted approximately 97 seconds, the aircraft experienced intense vertical air currents. The flight crew subsequently diverted the aircraft to Fortaleza, Brazil (SBFZ), for medical assistance. The incident resulted in 13 injuries, including 3 serious injuries (one flight attendant and two passengers) and 10 minor injuries. The aircraft sustained light damage to its interior due to passengers and crew members being thrown against the cabin ceiling. At the time of the encounter, the 'Fasten Seatbelt' sign was not illuminated, and several passengers and crew members were not wearing their seatbelts.
The investigation
CENIPA's investigation examined meteorological data, flight recorder information, and radar settings. Investigators analyzed satellite imagery and SIGWX charts, which indicated that the area was subject to embedded thunderstorms with tops reaching FL450. The investigation also reviewed the aircraft's radar configuration, noting that the radar was set to an 80 NM range with a TILT of -1°.
Findings
- Severe meteorological conditions caused the encounter, specifically intense convective processes from a cumulonimbus cell located less than 20 NM from the flight path.
- The aircraft was flying through a turbulence dome, a region of low radar reflectivity located above the top of a developing storm.
- The radar TILT setting of -1° may have prevented the detection of the weather cell, as the scan was likely focused on the upper portion of the cloud containing ice crystals rather than the more reflective liquid water layers below.
- The crew's use of the sidestick to counteract the turbulence may have contributed to the magnitude of the effects, as the inputs exceeded the limits of the Angle of Attack protection and caused the autopilot to disengage.
- There was an inadequate use of Flight Watch services, which could have provided the crew with the SIGMET alert regarding embedded thunderstorms.
Safety action
CENIPA issued recommendations to the National Civil Aviation Agency (ANAC) to disseminate the lessons learned from this report to increase pilot situational awareness regarding adverse weather. Additionally, it was recommended that ANAC work with the operator to reinforce training procedures regarding the effective use of onboard radar and aircraft control techniques to avoid severe turbulence.