As you will be aware, there are many media reports at the moment about turbulence following the Singapore Airlines event that took place on 21 May 2024 and is reported to involve one fatality. While we do not want to prejudice the investigation in any way, we thought it might be useful to share again this article that was originally published in the 1st Edition of the Conversation Aviation magazine in 2023. You can access the full magazine on the Community Site here.
This article was originally provided by an operator from their own magazine and might contain references to Airbus specific configurations. Obviously you would need to consider these in relation to the specific aircraft type you operate.
Introduction
Turbulence injuries are the most common cause of injury in aviation. This article highlights the main weather phenomena that lead to turbulence as well as some of the best practices that you can use to manage the risks to both cabin crew and passengers.
Turbulence encounters may cause injuries to passengers and cabin crew. However, by using best practices, applying the recommended techniques, and following procedures will help to reduce the risk of injuries. This co-written article from cabin safety and flight ops safety aims to review some of the different types of turbulence, highlight the associated risks, and provide links to useful references that are available to avoid- and mitigate these risks.
Some potential causes of turbulence
There are various sources of turbulence that you might encounter:
Convective weather
"During descent, crew is aware of a convective cloud ahead. The convective cloud is not displayed on the WXR Radar despite a range of tilt settings. With the lack of return showing on the WXR Radar (WXR Radar was operating and displaying normally) coupled with the appearance of the cloud, a weather deviation is not considered to be necessary. At around FL120 approx. two or three mins after the crew were requested to begin preparing the cabin for landing and were moving through the cabin, the aircraft entered the cloud and encountered moderate turbulence for approximately 25 to 45 seconds whilst the cabin crew was walking through the cabin.”
Convective weather remains an major cause of turbulence. Always consider that a convective cloud may be dangerous, even if the weather echo is weak (the weather radar mainly detects water droplets).
The flight crew should use the weather reports and charts to determine the location and altitude of possible convective weather and Cumulonimbus clouds (CBs). The Pilot's iPad checks for new NOTAMS and weather “real time” when the briefing pack is refreshed. Regularly updating weather information throughout a duty is important because meteorological conditions can be very dynamic. Another potential source of information on convective weather may be an online weather radar.
Sharing information about the weather conditions with the cabin crew during the interactive brief helps to create a shared mental model on the expected meteorological conditions and what this means for managing the flight. Knowing the capabilities, limitations and operational procedures of the on-board weather radar helps ensure correct tilt management (if applicable) and a correct assessment of any storm cells you may encounter.
Once assessed and when deemed required, perform a lateral avoidance instead of a vertical avoidance. Vertical avoidance is not recommended, particularly at high altitude, due to the reduction of buffet and performance margins as well as the potential for strong turbulence (turbulence and a significant concentration of ice crystals can extend well above the visible top of a CB). In addition, some convective clouds may have a significant and unpredictable build up speed. It is therefore preferred to deviate around the “area of greatest threat” by at least 20NM upwind. Avoid flying underneath CBs even in visual conditions and if it is decided to overfly, apply a vertical margin of at least 5000’ from the “area of greatest threat”. You should provide your crews with further operational guidance on handling Convective Weather and Ice Crystals.
Different aircraft have different types of weather radars, even within a single fleet. So make sure crews know how their weather radar operates. Manufacturers provide various articles and videos that give guidance on the operation of the different types of installed weather radars.
Clear air turbulence
“During the cruise the crew were out with the trolleys when we had severe turbulence. The trolleys lifted off the floor at which point we had “cabin crew and passengers be seated immediately”.
Clear Air Turbulence is caused by the speed difference of air masses at high altitude. Regularly updating weather information during a duty and using significant weather charts to determine potential locations of Clear Air Turbulence is considered the main method in identifying areas where it may be present.
The Shear Rate (SR) value on the Operational Flight Plan (OFP) provides an additional source of information to crew. SR signifies a vertical windshear value in meters per second per thousand feet. The SR value is determined by quantifying the difference in wind speed and direction for the wind 2000 feet above and 2000 feet below the planned altitude using a predetermined algorithm. The higher the SR value, the greater the difference in wind speed and direction between the two altitudes. This information is to be used as guidance only and should be correlated with other available information such as SIGMETS and SIG WX Charts. Actively monitoring the radio frequency for pilot reports of encountered turbulence is also helpful in identifying these areas.
If you encounter Clear Air Turbulence, consider avoiding it vertically, keeping in mind that the buffet margin reduces as the altitude increases (and vice versa).
Wake turbulence
Wake turbulence rolls-up into a pair of coherent, counter rotating vortices that can persist for some minutes behind an aircraft’s flight path. This wake turbulence usually moves downward and laterally with the wind. The intensity of the vortex and the dissipation time depends upon factors as weight, size, speed of the aircraft and atmospheric conditions (calm weather creates the most critical situation).
Complying with separation minima is the main method to reduce encounters of wake turbulence. If it is suspected that the aircraft is encountering or may encounter wake turbulence, an upwind lateral offset can be used to avoid the wake turbulence (this however provides no guarantee of avoiding wake turbulence). During final approach, the crew should remain on the standard approach slope as a deviation does not guarantee avoidance of the wake turbulence and may introduce other risks.
Airlines should have clear guidance and training material for crew on handling significant wake turbulence encounters. The Flight Crew Training Manual advises, do not use the rudder, keep the AP ON and if the AP is off: release the controls and wait for stabilization of the aircraft prior to rolling wings level and re-establishing the desired trajectory.
Operational considerations for flight crew
If turbulence is expected, the crew must set the SEAT BELTS switch to ON to prepare passengers and prevent injuries in the cabin. All loose equipment must be secured in both the cockpit and the cabin.
When taking off in high turbulence, our training manual section on Weather Turbulence recommends waiting until target speed + 20kts (limited to VFE-5) before retracting the slats/flaps (e.g. the flight crew must wait for F+20 kt before setting Flaps 1).
In flight, as the flight controls are designed to cope with turbulence, it is recommended to maintain AP/ATHR ON (for severe turbulence refer to the QRH). This also applies for the approach, though if during the approach it is considered that A/THR is operating unsatisfactory: disconnect A/THR and use manual thrust (balance against the increased workload).
Severe turbulence as characterized by large, abrupt changes in altitude and/ or attitude with large variations in airspeed should be avoided. If these conditions are encountered, action the QRH Severe Turbulence procedure and request a maintenance inspection (turbulence check).
Management of turbulence as a crew
It is essential for the cabin and flight crew to work together as one team to effectively manage the risks associated with turbulence. Practice shows that turbulence in the rear galley is likely to be perceived as worse than in the front of the cabin.
Having reviewed the relevant charts and weather information, the flight crew should use the interactive briefing to inform the cabin crew about the potential for turbulence and provide further information on the type, severity, duration and location of any expected turbulence.
When expecting turbulence in the descent to destination, consider asking the cabin crew to prepare the cabin for landing at such a time so that the cabin is secure when the turbulence is expected to start (contrary to asking the crew to prepare the cabin for landing when the turbulence starts).
Cabin crew are instructed to sit down and protect themselves when it is considered unsafe to move through the cabin. This may mean that the cabin is otherwise not secured on time.
When severe turbulence is either encountered or expected and insufficient time is available for normal procedures, make a PA to instruct the cabin crew and passengers to be seated immediately. When it is subsequently safe to move again in the cabin, make a further PA to return to normal cabin crew operations. Making a PA both in advance and during turbulence is considered a great way to keep your customers informed and reassured. It also really supports the cabin crew and will make a difference to any nervous passenger.
The key points:
- Turbulence encounters may cause injuries to passengers and cabin crew. Using best practices, applying recommended techniques, and following procedures will help to reduce the risk of injuries.
- Turbulence in the rear galley is likely to be perceived as worse than in the front of the cabin. Cabin and flight crew working together as one team is essential in effectively managing the risks associated with turbulence.
- If turbulence is expected, the crew must set the Seat Belts switch to ON, to prepare passengers and prevent injuries in the cabin. All loose equipment must be secured in both the cockpit and in the cabin.
- Always consider that a convective cloud may be dangerous, even if the weather echo is weak (the weather radar only detects water droplets).
- Making a PA both in advance and during turbulence really helps to reassure passengers and also supports the cabin crew in their duties.
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