Air France A332 over Tanzania on Feb 27th 2012, temporary loss of control in turbulence

Last Update: September 10, 2013 / 14:47:48 GMT/Zulu time

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Incident Facts

Date of incident
Feb 27, 2012

Classification
Report

Airline
Air France

Flight number
AF-3575

Departure
Antananarivo, Madagascar

Destination
Paris Charles de Gaulle, France

Aircraft Registration
F-GZCG

Aircraft Type
Airbus A330-200

ICAO Type Designator
A332

An Air France Airbus A330-200, registration F-GZCG performing flight AF-3575 from Antananarivo (Madagascar) to Paris Charles de Gaulle (France), was enroute anout 30 minutes into the flight when the crew received an ACARS message describing satellite images showing a strong convective zone parallel to latitude S12.5 degrees, further north isolated convective cells as far as north as S02.5 degrees. The crew continued the flight and nearing S12.5 degrees needed to perform a number of deviations around cells. The aircraft climbed to FL360. About 10 minutes after crossing latitude S12.5 the captain, pilot flying, switched his navigation display to 160nm, the weather radar scanning around a center tilt angle of -1.5 degrees, the aircraft moved in clear skies with view of stars, no returns on the weather radar. Dar es Salaam center queried whether the aircraft could climb to FL380, the crew declined due insufficient margin to the maximum cruise level possible. The aircraft was on autopilot and autothrust, LNAV, ALT and SPEED modes active. Another 6 minutes later the cruise speed 0.81 mach suddenly starts to increase, the captain reduces the ND range to 80nm, the crew notices a flash and a cloud to the right of the aircraft, but still no return on the weather radar. When the speed increased through 0.83 mach the crew selected 0.78 mach into the speed window and extends the speed brakes for about 15 seconds, the speed reduces to 0.79 mach but increased to 0.82 mach again. Another flash is observed immediately followed by severe turbulence, the "fasten seat belt" signs automatically illuminate and the autopilot trips off, the aircraft climbs sharply despite the captain issuing nose down inputs. An attempt to re-engage the autopilot results in immediate disconnection of the autopilot, autothrust automatically disconnected just prior to the first officer disengaging the autothrust system. The captain manages to level the aircraft off at FL380, then descends the aircraft back to the cleared flight level 360. The automation was reconnected and the flight continued to destination without further incident and landed safely in Paris. However, a passenger and a flight attendant had received minor injuries in the turbulence encounter.

The French BEA released their final report in French concluding the cause of the occurrence was:

The non-detection of a rapidly developing convective zone and a thunderstorm cell in the Tropics. The area was especially difficult to detect due to the extermely rapid development of the cell.

Contributing factors were the lack of tools to detect developing convective cells more reliably and efficiently and the improper adjustment of ND range not permitting the optimal detection of weather.

Given the extremely rapid development of the cell it is not sure that the weather radar would have been able to pick that cell up even with optimum range selected however.

The appropriate response of the crew at the flight controls permitted to maintain "good control" of the aircraft when the flight conditions suddenly became very difficult.

The BEA analyzed based on satellite images and weather data: About 15 minutes prior to the turbulence encounter the aircraft was about 120nm from the center of the convective area that was just about forming, the cell was not yet visible on infrared satellite images. At that point it is safe to assume that the zone would not be detectable.

The cell was still not visible on infrared satellite images 12 minutes prior to the turbulence encounter, the next satellite image past the encounter showed the cell.

About 10 minutes prior to the turbulence encounter the aircraft was 80nm from the center of the convective activity, that had grown significantly, at that point it can be assumed that the cell was detectable with the proper range and tilt angle. About 5 minutes prior to the turbulence encounter a range of 80nm on the navigation display would not have permitted the cell to be detected, a range of 40nm however would likely have detected the weather.

According to the flight data recorder the autopilot disconnected the first time because of high acceleration and sharp control inputs necessary causing the autopilot to command three different large countering deflections of control surfaces within 8 seconds. When the autopilot (left hand) was re-enagaged by the captain, it disconnected again within 2 seconds this time because the flight guidance systems had rejected the inertial reference data. Flight guidance system 2 engaged instead of flight guidance system 1. The autothrust system disconnected automatically, just prior to the manual deactivation, due to flight guidance system 2 also rejecting inertial reference data, and both flight directors were withdrawn from display. The investigation reported that it was not possible to determine the causes for both FMGEC systems to reject the inertial data. The total time of both flight directors being removed from display lasted for about 20 seconds.

The BEA reported that the captain provided testimony that the severity of the turbulence rendered all instruments unreadable due to vibrations, the resulting noise in the cockpit made any communication with other crew members impossible. The captain said, that following the initial surprise he experienced sort of a shock. The first officer provided testimony stating the severity of the turbulence did not permit any routine tasks and pointed out the intensity of the wind noise. He started to focus to monitor key parameters like speed, attitude and power. The first officer did not notice that the aircraft had deviated 2000 feet from assigned altitude, he thought the captain had managed to maintain the assigned flight level.

The BEA issued a number of safety recommendations regarding use of weather radar as well as research and improvement of weather radar systems.