A359, vicinity Cayenne French Guiana, 2021
A359, vicinity Cayenne French Guiana, 2021
Summary
On 5 December 2021, an Airbus A359-900 crew encountered a very brief episode of unexpected clear air turbulence associated with visible signs of convective weather in the vicinity. Not having had prior warning, the senior cabin crew member fell and was seriously injured. The investigation concluded that the risk of turbulence prevailing for the location and season as the end of daylight approached was greater than perceived by the pilots, despite their familiarity with the local area and its weather. The investigation further concluded that releasing the cabin crew from their previously secured positions had been inappropriate.
Flight Details
Aircraft
Type of Flight
Public Transport (Passenger)
Flight Origin
Intended Destination
Take-off Commenced
Yes
Flight Airborne
Yes
Flight Completed
Yes
Phase of Flight
Descent
Location - Airport
Airport
General
Tag(s)
CVR overwritten
LOC
Tag(s)
Environmental Factors
WX
Tag(s)
CAT encounter
CS
Tag(s)
Turbulence Injury - Cabin Crew
Outcome
Damage or injury
No
Non-aircraft damage
No
Non-occupant Casualties
No
Occupant Injuries
Few occupants
Off Airport Landing
No
Ditching
No
Causal Factor Group(s)
Group(s)
Aircraft Operation
Safety Recommendation(s)
Group(s)
None Made
Investigation Type
Type
Independent
Description
On 5 December 2021 an Airbus A359-900 (F-HNET) being operated by Air Caraïbes Atlantique on a scheduled international passenger flight from Paris Orly to Cayenne encountered a very brief turbulence as it descended though approximately 7,000 feet in day VMC whilst close to but clear of cloud but in the vicinity of convective activity. The cabin crew were carrying out routine duties having been given explicit clearance to do so by the captain.
Investigation
A Serious Incident Investigation was carried out by the French Civil Aviation Accident Investigation Agency, the BEA using relevant QAR data but as the CVR was not isolated after landing, relevant data from it was lost. Relevant recorded ATC and meteorological data was available.
The training captain in command had “around 10,000 hours” flying experience and was accompanied by a first officer who “had logged more than 5000 hours” flying experience. No information was published on the pilots’ aircraft type experience, despite its potential relevance.
As descent from the final cruise altitude of FL400 was about to be commenced, the flight crew reported having anticipated an initial area of potential turbulence. After speaking with the SCCM and advising them to temporarily suspend cabin service and secure themselves, the captain switched on the seat belt signs and made a corresponding announcement to the passengers. The aircraft subsequently encountered turbulence lasting around 30 seconds, during which the recorded vertical acceleration varied between +0.43g and +1.71g, and lateral acceleration varying between -0.08 g and +0.09 g. Simultaneously, airspeed varied between M0.79 and M0.88 as vertical speed initially increased to +1,400 fpm before deceasing to - 1,250 fpm. The AP and A/THR remained engaged.
Once clear of this turbulence, the captain informed the SCCM that they could resume normal tasks and advised that descent was about to commence. The seatbelt signs were left on and both pilots stated that they had continued to “visually avoid the cloud cells by flying alongside the cloud masses and between two cloud layers”. Subsequently, suspecting they were about to enter a new area of potential turbulence, the captain again instructed the cabin crew that they should secure themselves but as FL 100 was approached, and believing that the risk of turbulence had passed, the captain advised the SCCM that the cabin crew could leave their seats in order to finish preparing the cabin for landing.
A short time later, when descending through 7,037 feet with nightfall imminent, a second very short turbulence encounter occurred. The recorded vertical acceleration varied between +0.42g and +1.82g, as the lateral acceleration varied between -0.14g and +0.12g, and the 1,100 fpm rate of descent momentarily became a 430 fpm rate of climb before the 1,100 fpm descent was immediately restored. Again, the AP and A/THR remained engaged throughout. However, this time the SCCM and two other cabin crew in the rear of the aircraft reported having felt “a quick, rough jolt” and lost their footing. The SCCM fell and sustained what was subsequently found to be a double ankle fracture, and their duties were taken over by one of the other 8 cabin crew. The remainder of the flight was uneventful. Medical assistance was requested and acknowledged, and the airport RFFS were in attendance as the aircraft reached its assigned parking position.
The prevailing weather in the area corresponded with the pilots’ preflight expectations for the descent into Cayenne, with storms associated with Towering Cumulus and Cumulonimbus. The French Meteorological Office advised that such conditions were normal for this season as the end of daylight approached.
The exact position of the aircraft at the time of the upset on the prevailing rainfall radar picture was found to have put the aircraft “at the edge of a line of rainfall where the convection was strongest”. It was noted that the vicinity of such cloud edges downstream of the line of movement of convective clouds was typically associated with significant strong turbulence and wind shear.
The flight track and vertical profile with the position of the two turbulence encounters marked. [Reproduced from the Official Report]
The aircraft was equipped with the latest onboard weather radar which during a descent in automatic mode scans within a nominal +/- 4000 feet of the projected vertical flight path based on the flight path angle and then indicates if a weather return is inside this envelope. The aircraft type FCTM was noted to recommend avoiding convective cells laterally rather than vertically, into the wind rather than downwind and if possible avoiding any area of significance by at least 20 nm. However, it was noted that even the most advanced weather radars rely on detection of water droplets and will not detect clear air turbulence or necessarily turbulence within an apparently benign layer cloud. It was noted that the EFB provided to flight crew by the operator included an application which enabled them to access up-to-date weather information via SATCOM, which may have been relevant to turbulence risk assessment but it was not possible to establish what that might have included or whether specific data had been accessed.
The Investigation noted that turbulence injury events have been the subject of review by various agencies, including one by the Japan Transport Safety Board in 2015 and another by the US National Transportation Safety Board in 2021. It also noted the BEA Investigation into another turbulence event which also led to cabin crew injury and its resulting safety recommendations regarding both ATC and on-aircraft weather information.
The Conclusion of the Investigation was that the turbulence encountered was probably generated by a convective cell close by, which the crew may not have been able to detect or may have underestimated their distance from it and/or the extent of the turbulence risk.
The Final Report was initially published in the definitive French language on 26 December 2022 and this was followed on 28 February 2023 by an English Language translation.
Related Articles
- Clear Air Turbulence (CAT)
- Turbulence
- Cumulonimbus (Cb)
- B738, en-route, near Cuneo northwest Italy, 2021
