Turbulence

Turbulence

Turbulence is defined as a disturbed, irregular flow of air with embedded irregular whirls or eddies and waves. An aircraft in turbulent flow is subjected to irregular and random motions while, more or less, maintaining the intended flight path. Turbulence is the result of atmospheric or environmental effects:

• Clear Air Turbulence Phenomenon: Clear Air Turbulence (CAT) layers are found along front lines and their jet streams. These areas of vertical exchange of air mass are the most dynamic and significant where two tropopauses overlap each other. When turbulence becomes excessive, an altitude change is more efficient than a track change.

• Convective Induced Turbulence: This type of turbulence is due to heat radiation from different ground states, e.g. forests, lakes, rocks, RWYs etc. Climb out and approach phase can be uncomfortable.

• Topographically Induced Turbulence: Topographically induced turbulence occurs in strong wind conditions behind hills, buildings, etc. These conditions may also cause wind shear.

• Wake Turbulence: Behind aircraft consists of two counter-rotating cylindrical vortices. The pressure differential between the upper and the lower side of the wing triggers the roll up of the airflow aft of the wing, resulting in swirling air masses trailing downstream of the wing tips. Pilots should avoid a region within less than 200ft of the vortex core. When flying on track systems in oceanic or remote areas offset procedures (i.e. SLOP) may be applied.

En-route turbulence accounts for a substantial number of passenger and/or cabin crew injuries and can occur at anytime and at any altitude. Turbulence can be expected, or it can be sudden and unexpected. Intensity can vary and is relative to location of the occupants in the aeroplane (generally the rear of the aeroplane will experience greater turbulence intensity then the front).

Turbulence injury prevention takes a combination of teamwork and personal responsibility. The responsibility for preventing turbulence injuries will continue to rest with each individual crew member. Crew members should keep each other informed of conditions and take appropriate actions to avoid injuries.

Procedures for flying in severe turbulence are described in FCOM PRO-SUP-91-10 Severe Turbulence.

The Commander should include a weather turbulence briefing with the standard predeparture briefing, and the cabin crew should pay particular attention to turbulence forecasts. The weather briefing should contain the following:

• Discussion of the critical exposure periods (which could include take-off, cruise or known areas of turbulence and descent);
• Expected en-route weather;
• Forecast turbulence location (in terms of flying time and degree of reported turbulence);
• Communication of possible service modifications prior to expected turbulence encounters;
• Establishment of the “all clear” signal, usually done by turning the Seat Belts sign to OFF.

During the welcome PA, the CIC shall advise passengers to keep their seat belts fastened during the entire flight whilst seated.

While in flight, the Commander should communicate with the CIC if turbulence is expected or encountered. He will call the CIC to the cockpit or turn the Seat Belts sign to ON. The CIC should communicate this information to the other cabin crew members. Cabin crew should then prepare the cabin according to the level of the turbulence anticipated.

Communication must flow two ways. If a reasonable amount of time has elapsed with no turbulence and the Seat Belts sign remains ON, CIC should initiate contact with the Commander via interphone in order to determine if it is safe to resume duties.

The following items shall be accomplished by the CIC when he is informed by the flight crew that turbulence is expected:

• Ask how much time is available prior to encountering, anticipated intensity and the duration of the turbulence;
• Ensure that all cabin crew members are given the same information;
• Coordinate with the flight crew regarding appropriate announcements advising the passengers of the situation, including fastening their seat belts;
• Determine the level of service if any;
• Advise the Commander when cabin is secure;
• Confirm any other specific information or instructions.

Cabin crew members should:

• Ensure all occupants are seated and seat belts fastened - infants should be secured using infants seat belt;
• Ensure all lavatories are vacated;
• Secure all loose items in the flight and galleys - all carts should be stowed andlocked;
• Take designated cabin crew seats and fasten seat belts and shoulder harness;
• Remain seated until Seat Belts sign is switched OFF.

When the turbulence has ended and the Seat Belts sign has been switched OFF, the cabin crew shall check passengers, cabin and flight deck to ensure there are no adverse effects arising from the turbulence encounter.

If conditions dictate (moderate or greater intensity turbulence) and Seat Belts sign has not been switched ON, cabin crew shall immediately take the nearest seats or jump seats and fasten seat belts and shoulder harnesses. CIC or any other cabin crew member should make public address instructing passengers to return to their seats and fasten seat belts.

When possible, the Commander shall be informed via interphone of cabin status (secured or unsecured).

Turbulence has been divided into four categories based upon the severity of the encounter:

Turbulence AIREP (ICAO Doc 4444)

When encountering turbulence, pilots shall report such conditions to ATC as soon as practicable. The turbulence PIREP should state at least:

• Aeroplane position;
• Aeroplane altitude or flight level;
• Turbulence intensity.