Emirates B773 near Beirut on Jan 17th 2021, severe clear air turbulence injures 7 people

Last Update: August 9, 2021 / 15:57:22 GMT/Zulu time

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Photo of Emirates Airlines A6-EPN, Boeing 777-300 — Emirates Airlines A6-EPN, Boeing 777-300 (Photo credit: Samee55 / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Jan 17, 2021

Classification
Report

Airline
Emirates Airlines

Flight number
EK-957

Departure
Dubai, United Arab Emirates

Destination
Beirut, Lebanon

Aircraft Registration
A6-EPN

Aircraft Type
Boeing 777-300

ICAO Type Designator
B773

An Emirates Boeing 777-300, registration A6-EPN performing flight EK-957 from Dubai (United Arab Emirates) to Beirut (Lebanon) with 50 passengers and 14 crew, was descending through FL292 when the aircraft encountered severe turbulence causing serious injuries to a passenger and minor injuries to 2 passengers and 4 crew. The aircraft continued to Beirut for a safe landing.

The aircraft remained on the ground in Beirut for 3.5 hours, then departed for the return flight.

On Aug 9th 2021 the United Arab Emirates Civil Aviation Authority (GCAA) released their final report concluding the probable cause of the accident was:

The Air Accident Investigation Sector determines that the cause of the Accident was the significant vertical g-forces imposed on the Aircraft because of severe clear air turbulence, which caused an unsecured passenger to be forcefully lifted off her feet and impact cabin furnishings resulting in her right foot fracture serious injury.

Contributory Factors

- The influence of the jet stream and thunderstorm in the flight path area was significant enough to produce severe turbulence.

- The flight crew decision making lacked critical information contained in SIGMET 3 issued by LCLK MWO (covering the period from 0530 to 0930) which forecasted severe turbulence between FL260 and FL390, south of latitude N3430.

- The format of the SIGMET issued by LCLK MWO was different from the recommendations contained in ICAO Annex 3 and EU regulation No. 2020/469 such that the Weather Services International Fusion application (WSI Fusion) applied by the Operator’s flight dispatch department did not generate a timely alert for SIGMET 3 report issued by LCLK MWO.

The GCAA analysed that both crew and ATC were aware of the significant weather forecast indicating severe turbulence was possible.

The GCAA wrote:

Communication with Nicosia air traffic control (ATC) (area control center “ACC”) prior to the top of descent indicated that both ATC controller and the flight crew were aware of the significant weather. The initial decision taken by the flight crew was to request clearance for deviation from ATC as the weather radar was indicating cumulonimbus (CB) clouds approximately 80 nautical miles (NM) ahead of the Aircraft. ATC advised the flight crew to head directly to a new waypoint (ZALKA) which the Commander accepted and accordingly selected 042 degrees heading which would take the Aircraft south of the CB.

The flight crew were comfortable with the new heading especially as the weather returns on the navigation display indicated that the cloud cells were 50 to 120 NM to the north of the flight path.

In anticipation of turbulence during descent, the Commander turned the seatbelt sign to ON at FL360. The flight crew stated that, during the first three minutes of descent, there was no weather radar indication on the navigation display of any significant weather (including red speckles) or any cloud formation and precipitation that may form a kind of threat that would have warranted focused attention.

When the severe clear air turbulence started, the flight crew immediately implemented the SOP by arresting overspeed by use of the speedbrakes, and selecting the appropriate autopilot modes.

The Investigation concludes that the flight crew operational decisions were appropriate based on the available information. This included monitoring and settings of the weather radar, the OFP significant weather chart, communication with Nicosia ATC and the Aircraft automation.

...

The significant meteorological conditions that were prevailing in Nicosia and Beirut FIRs were forecasted in the high-level prognostic significant weather (SIGWX) chart contained in the operational flight plan for flight EK957.

The forecast included information about occasional embedded CB with tops of 30,000 ft, and moderate turbulence, increase to severe occasionally, between FL380 and FL280, approximately north of latitude N32.0 where the Nicosia and Beirut FIR are within. In addition, the Aircraft flight path and altitude within Nicosia FIR took it just north of the northern hemisphere jet stream which was forecasted at FL370 with maximum speeds of up to 170 kt and close to latitude N32.0.

On the day of the flight, because of the prevailing significant weather phenomena of thunderstorms and severe turbulence, both MWO of LCLK and OLBA had published significant weather information (SIGMET) at regular intervals of approximately every four hours.

The significant weather affecting the FIR of Nicosia was confirmed by the satellite multispectral image captured at 0800 on 17 January 2021, which also indicated areas of lightening close to the Aircraft flight path in Nicosia FIR.

When the EK957 flight crew communicated with Nicosia ATC for the first time (at approximately 0757 UTC), SIGMET 3 and 4 reports issued by LCLK MWO were in effect for Nicosia FIR. Of the two SIGMET reports, SIGMET 3 provided information about severe turbulence forecast that would take place during the period from 0530 to 0930, between FL260 and FL390, south of latitude coordinates N3430, and no change was expected over the 4-hours period. The FDR data confirmed that the first region of severe turbulence that the Aircraft encountered occurred between pressure altitude 28,400 ft and 25,500 ft, close to N32.857 latitude coordinates which was almost similar to the SIGMET 3 forecasted flight level and location.

The turbulent atmosphere that the Aircraft entered was due to the sudden reduction in the horizontal wind magnitude of approximately 49 kt, which resulted in significant variation of gloads on all axes. The calculated vertical wind speed was mostly near zero feet per second on average.

The Investigation concludes that the significant turbulent atmosphere the Aircraft transverse during the descent was due to the change in wind speeds that was most likely influenced because of the jet stream and the thunderstorms which was affecting Nicosia FIR.

Based on the analysis and calculation performed by the Aircraft manufacturer, the influence of the jet stream and thunderstorm that were present in the area was capable of producing significant turbulence. Most likely, the turbulence encounter was associated with clear air turbulence.

...

On 17 January 2021, SIGMET 3, issued by LCLK MWO, contained forecast of occasional severe turbulence between FL260 and FL390. The SIGMET message was received by WSI Fusion interface. However, the text in the message was formatted as “BTN FL260 AND FL390” which was not a recognized format to the WSI Fusion. Consequently, the WSI Fusion could not compile the message and stopped analyzing the SIGMET information at the characters “FL260” because the free text ‘AND’ was not compatible with the software programming language.

The standard format SIGMET of Annex 3 to the Chicago Convention utilizes slash ‘/’ marks to separate the flight levels.

When SIGMET 3 was issued at 0515 by LCLK MWO, the Aircraft was in the cruise phase in Jeddah FIR, and was about 2 hours 43 minutes away from Nicosia FIR entry point. However, an alert was only generated at 0805 when the Aircraft flight level reached FL260 during the descent in Nicosia FIR and matched with the flight level recognized by the WSI Fusion.

When the ACARS alert message was eventually transmitted to the Aircraft at 0809, the sterile cockpit policy was in effect, therefore it was kept on-hold and not displayed to the flight crew. Even if the flight crew had access to the ACARS message, at the time the alert was transmitted it would not have benefited the flight crew because the Aircraft had already passed the flight level stated on the alert message.

All SIGMET reports should be given timely attention and communicated to flight crews that can assist their decision making process. When a hazard of turbulence is not timely alerted and avoided, mitigation opportunities of risk of severe jolts, structural damage to aircraft, airspeed fluctuations and huge variation in g-loads, and the consequent injury to crewmembers and passengers, will be compromised.