Emirates A388 over Mozambique on Jan 16th 2020, turbulence injures passenger
Last Update: November 20, 2020 / 18:35:31 GMT/Zulu time
On Nov 20th 2020 the UAE GCAA released their final report stating they had notified Mozambique's Instituto de Aviação Civil de Moçambique (IACM) about the occurrence over Mozambique (and thus in charge of the investigation), however, the IACM never acknowledged receipt of the notification. Hence "The AAIS, being the investigation authority of the State of the Operator and State of Registry of the Aircraft, opened an investigation into this occurrence."
The GCAA concludes the probable causes of the accident were:
The Air Accident Investigation Sector of the United Arab Emirates (AAIS) determines that the cause of the Accident was 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 crewmembers.
The Investigation determines that the following were contributory factors to the Accident:
(a) After entering BEIRA FIR and 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.
(b) There was insufficient time for the cabin crew to secure the cabin after the seat belt sign was turned ON.
The GCAA summarized the sequence of events:
The Commander, occupying the left seat, was the pilot flying (PF). He stated that prior to the turbulence encounter, the daylight flight was uneventful with no avoidance actions required due to weather.
After entering BEIRA flight information region (FIR), Mozambique, at flight level (FL) FL400 close to waypoint OKBIM, the flight crew stated that there was light turbulence with the weather radar displaying that the weather was off-path on the navigation display (ND) and beneath the Aircraft. Soon after, several magenta spots appeared on the weather radar along the flight path indicating that there were areas of wet turbulence within 40 nautical miles (NM) ahead of the Aircraft.
At 1314:24 UTC, approximately six hours after departure from OMDB, the Aircraft experienced moderate to severe turbulence at FL400 within BEIRA FIR. The operational flight plan (OFP) significant aeronautical weather chart had forecast the occasional presence of convective weather activity containing embedded cumulonimbus clouds (CB) up to an altitude of 52,000 feet (ft) in this area.
During the turbulence encounter, the Aircraft autopilot and autothrust remained engaged and there were no operational exceedances.
The turbulence lasted for approximately 30 seconds and resulted in a serious leg injury to an unsecured passenger on the upper deck. There was no reported damage to the Aircraft cabin.
The Commander decided to continue the flight to the destination as the passenger’s injury was non-life threatening and the Aircraft performance was not affected. The remainder of the flight, lasting 1 hour 46 minutes, was uneventful.
The GCAA reported that prior to the turbulence encounter the captain of A6-EEN had seen a Qatar Airways Aircraft flying overhead at FL410 in opposite direction, the flight was identified as QR-1364, an Airbus A350-900 registration A7-ALC enroute from Johannesburg to Doha (Qatar). The GCAA analysed:
Prior to the turbulence encounter at FL400, an Airbus A350 aircraft, had passed through this area approximately 11 to 12 minutes earlier. Because of insufficient information, the flight level of QR1364 at this stage of flight could not be confirmed as the aircraft was climbing from FL390 to FL410.
European Union Aviation Safety Agency (EASA) Safety Information Bulletin SIB No. 2017-10 ̶ En-route Wake Turbulence Encounters, issued on 22 June 2017, indicates that the basic effects of wake turbulence encounter on an aircraft are induced roll, vertical acceleration (can be negative), and loss or gain of altitude, while emphasizing that the greatest danger is typically the induced roll that can lead to a loss of control and possible injuries to cabin crew and passengers. EK763 did not experience any significant disturbance on the lateral axis as the roll was a maximum of two degrees to the left and right during the 30 seconds of turbulence.
The SIB states that en-route, the wake vortices evolve at altitudes at which the rate of decay leads to a typical persistence of two to three minutes, with a typical sink rate of about 400 feet per minute. Taking into consideration that QR1364 had transitioned through the area of turbulence approximately 11 to 12 minutes before EK763 turbulence encounter; any wake vortices generated by QR1364 would have decayed in the interim.
The Investigation concludes that the changes to attitude and altitude of EK763 during the turbulence encounter were not due of wake turbulence and were most likely related to the prevailing convective weather wet turbulence cells.
The GCAA analysed:
The flight crew decided to maintain the planned flight path as the weather radar was showing the weather as off-path, indicating that the weather system threat was below the Aircraft by at least 5,000 ft. The flight crew did not receive any pilot reports nor air traffic control reports of turbulence or deviation within BEIRA flight information region (FIR), Mozambique, to influence their decision.
When updated en-route weather information is required, flight crew have the option to contact the Operator’s flight dispatch as the Operator does not provide live en-route weather information utilizing the flight crew electronic flight bag.
The flight crew stated that before entering the eastern region of central Africa, the flight was uneventful with no significant weather and they were aware of the threat of thunderstorms when flying through this area of Africa at this time of the year.
From 1311:37, with the Aircraft at 26 NM and 2 minutes 47 seconds from the turbulence encounter, the weather radar wet turbulence function detected wet turbulence which was visible as magenta on the navigation display (ND). This was confirmed by the Aircraft recorded flight data. However, it is most likely that the flight crew did not observe the on-path magenta cells from their onset. As reported by the Commander, when they eventually saw the magenta indications, they did not have time to make any changes to the ND gain. There was only sufficient time to turn the seat belt sign ON which was done just eight seconds before the turbulence commenced.
During the turbulence encounter, which was composed of headwinds and updrafts of up to 4,900 feet per minute, the Aircraft experienced load factors which changed rapidly to positive 1.75 g with a lowest value of positive 0.17 g, and altitude deviations ranging between positive 300 ft and negative 180 ft. The flight crew correctly executed the flight crew operating manual (FCOM) ̶ Abnormal and Emergency Procedures for Overspeed Prevention. The Commander extended the speed brakes and reduced the selected speed. An exceedance of maximum operating Mach (MMO) was avoided by the appropriate actions of the flight crew and the Aircraft automated systems. During the 30 seconds of the turbulence encounter, the Aircraft stayed within the normal flight envelope with the autopilot and autothrust engaged.
The Investigation concludes that had the flight crew observed the magenta wet turbulence from the onset, it may have been possible to assess whether taking avoiding action would have steered the Aircraft away from any area of threat in addition to allowing more timely notification to the cabin crew to enable them to prepare the cabin in case of any turbulence.
In order to assist flight crew decision making regarding weather conditions, the Investigation recommends that the Operator enhance the ability of pilots to access updated weather information through the electronic flight bag.
For the different flight phases, including the cruise at FL400, the Aircraft was operated in the correct configuration and attitude with the autopilot and autothrust engaged.
At the beginning of the turbulence encounter at 1314:24, the flight data recorder (FDR) data indicated significant wind variations. This caused significant variations in the Aircraft attitude, altitude and a sudden airspeed increase. The Aircraft systems automatically responded and successfully avoided any overspeed.
Based on the Airbus analysis, the turbulence encounter resulted in the Aircraft its occupants experiencing significant variations of vertical and lateral load factor, which were consistent with the adverse wind variations.
The Investigation concludes that throughout the severe turbulence encounter the Aircraft remained controllable. The Aircraft systems functioned as designed, and automatically responded to sudden flight variations in order to avoid the overspeed.
The Aircraft’s weather radar system was of the latest modification status available from the Aircraft manufacturer and was standard across the Operator’s A380 fleet. The A380 weather radar (WXR) incorporates several automated functions with manual options for the flight crew. Pilots introduced to the capabilities of the weather radar as well as the meaning of the different colors displayed on the ND by eLearning sessions.
In accordance with standard operating procedures, for the flight, the Aircraft WXR and turbulence (TURB) functions were active with weather information displayed on the ND.
The weather radar turbulence (TURB) function detects wet turbulence and displays the area as magenta on the ND within the envelope of WXR TURB detection function being 40 NM ahead, 20 NM on both side of current Aircraft heading, plus/minus 5,000 ft of the Aircraft altitude. With the WXR in AUTO mode, the only indication of wet turbulence detection is the appearance of magenta on the ND as there are no cockpit alerts generated by the Aircraft systems.
For wet turbulence within a range of 40 NM ahead of the Aircraft, and provided the magenta is observed from the onset, the flight crew are required to make an immediate decision to divert by at least 5 NM from a single magenta cell and 20 NM in case of magenta when associated with other precipitation. As the decision on what action is required is based on when the flight crew observes the magenta and then processing this information, in case the flight crew fails to observe the magenta from the onset, means that there is a greater possibility that the aircraft will be affected by wet turbulence. For an aircraft in cruise, the distance covered in one minute is approximately 8 NM, thus the Investigation believes that without any aural cockpit alerting system for when wet turbulence is detected, reduces the time for the flight crew to make an appropriate decision.
Within 390 NM of the turbulence encounter, the Aircraft recorded flight data indicated that three times within a six-minute period the weather radar detected wet turbulence ahead of the Aircraft and displayed it in magenta on the ND. Again from 1311:37, and 26 NM from the turbulence, magenta areas were displayed on the ND within the WXR turbulence detection envelope of 40 NM ahead of the Aircraft. The detection of wet turbulence starting from 1311:37 is illustrated in Appendix D to this Report.
With the Aircraft less than 26 NM from the turbulence encounter, the Commander had reported that there was no indication of on-path precipitation except for some wet turbulence magenta areas which the Commander most likely observed less than two minutes before the turbulence occurred. Because the weather radar display on the ND of green, yellow and red areas are not recorded by the FDR, or quick access recorder (QAR), or cannot be deduced from indirect recorded parameters as done for magenta areas, the Aircraft manufacturer was not able to identify at the time of the event the area of greatest threat and the actual vertical and lateral margin between this area and the EK763 Aircraft trajectory.
Because the flight crew were not aware of the periods of wet turbulence from the onset, the WXR manual gain mode and elevation (ELVN) mode were not fully used to obtain the best cell echo, enabling the flight crew to assess the location of the area of greatest threat and the distance margin from the planned flight path. Even though the WXR AUTO mode is optimized for all flight phases, to assist the flight crew decision making the FCOM PROSUP- 91-30 ̶ Weather Radar, procedure recommends using the WXR manual mode temporarily “in order to monitor thunderstorm development and to obtain the best cell echo”.
The risk of a turbulence encounter in convective weather operation can be minimized by using all of the radar capabilities to identify the area of greatest threat and adopt the best trajectory providing sufficient separation from the area of adverse weather.
The Investigation concludes that the Aircraft weather radar was operating as designed. Similarly to the turbulence encounter as stated in Final Report of investigation file AIFN/0009/2019 (Appendix B to this Report), the EK763 flight crew did not use the full capabilities of the weather radar by adjusting the range and they did not effectively make use of the manual modes to enhance the echo returns. This would have assisted them in their assessment of the convective weather system. Knowing the capabilities and limitations of the weather radar installed on an aircraft is essential as well as being familiar with the techniques for using the weather radar effectively to optimize the opportunity to detect and avoid convective weather and wet turbulence.
The Investigation recommends that the Operator enhance the weather radar training information available to pilots including using the full capability of the weather radar to better analyze adverse weather situations to facilitate decision-making.
This article is published under license from Avherald.com. © of text by Avherald.com.
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