Description

On 16 January 2020, an Airbus A380-800 (A6-EEN) being operated by Emirates on a scheduled international passenger flight from Dubai to Johannesburg as EK763 was in the cruise over Mozambique at FL 400 in day VMC when it entered cloud and encountered unexpectedly severe turbulence. One unsecured passenger was seriously injured and several other passengers and unsecured cabin crew were lifted off their feet with some cabin crew impacting the ceiling or galley equipment but managing to avoid injury. The flight was completed to destination where the seriously injured passenger was hospitalised.

Investigation

A comprehensive Investigation was carried out by the UAE GCAA Air Accident Investigation Sector. Relevant data were obtained from both the FDR and the QAR but as the flight had continued for more than two hours following the turbulence encounter, relevant data from the CVR had been overwritten. Because the FDR was not designed to capture weather radar colour information, it was not possible to make an unequivocal determination of the aircraft flight path relative to the area of greatest weather threat as displayed on the NDs during the turbulence.

Assistance in the analysis of the FDR and CVR data was provided to the Investigation by Airbus. A two pilot crew was flying the aircraft with no relief crew on board or required and the Captain was acting as PF. No information was given on the flying experience of the pilots.

What Happened

The OFP (Operational Flight Plan) for the flight indicated that no significant weather was expected until just prior to entering the Beira FIR, Mozambique where a large area of significant weather activity typical of the ITCZ with isolated embedded Cb up to FL 520 affecting an area over the central and eastern border area of Africa was forecast. As a matter of routine, the aircraft weather radar and turbulence functions were selected to active mode and the ND was set to display weather information. For just under six hours of flight cruising at FL 400 there was, as forecast, no encounter with significant weather.

After entering the Beira FIR at FL 400 at M0.86, light turbulence was encountered whilst passing through an area of scattered clouds. The Captain stated that weather radar returns showing “three or four magenta spots” subsequently appeared on the weather radar within 40 nm of the aircraft position but the indicated cell tops were not above FL350. He was unable to recall when these magenta areas had appeared on the display but stated that after they appeared “there was insufficient time to deviate or to make any changes to the weather radar settings”. In response, the seat belt signs had been turned on but there was no corresponding communication with the cabin crew. 

The Operational Flight Plan significant weather chart provided to the flight crew. [Reproduced from the Official Report]

A satellite image of ITZ activity affecting the flight path at the time of the turbulence. [Reproduced from the Official Report]

Eight seconds later, as the aircraft entered cloud, a turbulence episode described by the flight crew as “moderate to severe” was encountered and lasted about 30 seconds and the First Officer responded by making a PA for cabin crew to take their seats. The AP and A/THR remained engaged and altitude variation was within the range FL 430 and FL 382. The automatic aircraft systems responded to the concurrent speed increase towards the Mmo of  M0.89 by deployment of the spoilers and the maximum speed remained just below it at M0.884 after which it reduced. Subsequently, the flight crew responded to a second increase towards Mmo by reducing the target speed from M0.86 to M0.76 and manually selecting the speed brakes to half maximum deployment. Examination of the recorded flight data showed that the turbulence episode had involved a change from a tailwind component to a headwind component and vertical speed of 4,900 fpm with positive load factors varying in the range 1.75g to 0.17g.  

As a subsequent medical assessment of the serious passenger injury concluded that it was not life-threatening and the aircraft systems were unaffected, the flight was continued to the intended destination and was without further event. The turbulence encounter was not subsequently reported to ATC.

Discussion

• Aircraft Systems - The automatic systems which helped control both airspeed and altitude worked as intended.
• Route Weather Forecast - The turbulence detection function of the weather radar indicated that there were several wet turbulence areas as the aircraft continued over Mozambique and Malawi confirming the accuracy of the convective weather forecast on the OFP significant weather chart.
• Relevant Procedures and Guidance - An examination of the operator’s SOPs and guidance for flight crew in respect of the need to avoid passenger and cabin crew injuries during significant en route turbulence encounters concluded that they were comprehensive and appropriate.
• Flight crew performance - Despite the fact that the OFP had accurately indicated that a large area of significant weather activity with “isolated embedded Cb up to FL 520” was likely to be encountered over Mozambique, it was concluded that the crew were not paying enough attention to their NDs as the flight approached a known area of turbulence risk and were unlikely to have observed the reported magenta cells when they initially appeared. This deprived them of the opportunity to prevent injury from a transient severe turbulence episode by giving (as required by SOPs) the cabin crew and passengers time to secure themselves safely and/or deviating around particularly active cells which may well be building. It was also noted that they did not use the full capabilities of the weather radar by adjusting the range and they did not effectively make use of its manual modes to enhance the weather returns displayed. 

The Investigation made a number of informal recommendations to the aircraft operator as a result of its analysis of the context in which the investigated event occurred as follows:

• In order to assist flight crew decision making regarding weather conditions, the ability of pilots to access updated weather information through the EFB is enhanced.
• The weather radar training information available to pilots including use of  the full capability of the weather radar to better analyse adverse weather situations to facilitate decision making is enhanced.
• The communication procedure between the flight crew and the cabin crew when the seat belt sign is turned on with information on the anticipated level of turbulence and the cabin services allowed is improved.
• The aircraft type option to enable an automated passenger announcement when the seat belt sign is switched on is reinstated.
• The audibility of the cabin chime when the seat belt signs are turned on is improved.

The Cause of the accident was formally documented as “the severe turbulence of vertical gust forces imposed on the aircraft as it operated within an area associated with wet turbulence cells, resulting in the forceful movement of unsecured passengers and cabin crew members”.

Two Contributory Factors were also identified as follows:

• After entering the Beira FIR, when wet turbulence was detected by the weather radar turbulence function, the flight crew did not use the full capabilities of the weather radar to obtain an accurate assessment of the distance of the area of greatest threat from the aircraft flight path.
• There was insufficient time for the cabin crew to secure the cabin after the seat belt sign was turned on.  

Safety Action opportunities relevant to the findings of this GCAA Investigation into action taken by Emirates as a result of the findings from a similar Airbus A380 turbulence event in July 2019 were noted to have included responses equally relevant to the broadly similar findings from this later event.

The Final Report was issued on 16 January 2020. No new Safety Recommendations were issued in this Final Report because the AAIS Final Report into a similar Emirates Airbus A380 turbulence event east of Chennai India in July 2019 issued on 12 August 2020 addressed similar findings with relevant safety recommendations and included the operator’s corresponding response and action.  

Related Articles

• Turbulence
• In-flight Seat Belt Requirements
• Weather Radar
• Cumulonimbus (Cb)