TURBULENCE
Turbulence is caused by air movement that is often invisible and unexpected. FAA guidelines require the use of seatbelts during takeoff and landing, while taxiing on the ground and whenever to the seat belts signs are on as a way to ensure safety against turbulence.
Statistics have shown that:
- turbulence is the major cause of injuries in non fatal accidents.
- around 58 people are injured annually by turbulence while not wearing seatbelts
- for the period of 1980 to 2004, there were 234 turbulence accidents – 298 injuries and 4 deaths
- most of the accidents occur above 30000 feet.
CAUSES OF TURBULENCE:
Causes of turbulence:
- atmospheric pressure changes - sudden changes in wind and temperature causes changes in the density of the air, creating turbulence
- jet streams - turbulence is usually found where there is a break in the jet stream due to the lowering or raising of the tropopause, on the colder side
- mountain waves
- thunderstorms - turbulence is usually associated with the convection activity, up draught and downdraught
- cold/warm fronts
CLASIFICATION OF TURBULENCE:
THERE ARE FOUR CLASSIFICATION:-
- Light: slight changes to attitude and/or altitude
- Moderate: variations in speed, altitude and altitude occur but the aircraft is remains in control
- Severe: large changes and variation of speed, altitude and altitude. There may be period where control of the aircraft is impossible. Damage of aircraft structure may occur.
- Extreme: prolonged expose can lead to loss of control and is capable of damaging the aircraft.
It is good to note that the severity of the PIREP issued depends on not only the severity of the turbulence but the size of the aircraft as well. Therefore, a report of light turbulence for a wide bodied jet may be more severe for a lighter jet.
A PILOTS EXPLANATION
| (Video embedded from YouTube on 18 september 2010) |
INCIDENTS:
CASE 1
United Flight 967, a Boeing 777, carrying 298 passenger and 10 crewmembers hit turbulence overhead Kansas. The flight was from Dulles International Airport to Los Angeles. They encountered “severe turbulence” leaving 30 passenger injured. The flight diverted to Denver.
| (Video embedded from YouTube on 18 September 2101) |
CRM MITIGATING FACTORS:
The avoidance and mitigation of the effects of turbulence encompasses all the CRM skills required of pilots. It requires the usage of judgement, situational awareness, sound decision making, good teamwork with the flight crew and the cabin crew and good communication.
METHODS USED:
PREFLIGHT:
- Obtain all pertinent documents, sigmet weather forecast and charts, satellite photos, turbulence charts and reports (PIREPS). This would help increase one's situational awareness of the areas of turbulence.
- Re routing the flight plan around known / forecasted areas of turbulence or weather systems. Flight plans can sometimes be defaulted to the most optimum and effecient routes. By actively intervening and rerouting, areas of turbulence can be circumnavigated.
- Establish communication and coordination with all crewmembers. Briefing the cabin crew on the weather conditions, duration, location and precautions to be taken. This allows all crewmembers to be aware of the areas of turbulence, especially the cabin crew who may be conducting service during the periods of turbulence.
DETECTION:
- Continuous tracking and updating of potential areas of forecasted enroute turbulence areas. Always being vigilant to the possibility of Clear Air Turbulence.
- Making PIREPS to inform ATC of turbulence encountered.
- Obtaining PIREPS and ride reports from ATC.
- Correct use of weather radar tilt and management.
- Continuous communication between the flight deck and the cabin to keep the cabin crew abreast of the flight.
- Early PA’s to facilitate the suspension of service. This facilitates the time required to secure the cabin in anticipation of turbulence.
- Use of seat belts sign. This allows the cabin crew members and the passengers sufficient time to return to their seats.
- Avoid any convective weather activity enroute by at least 20 nautical miles
PRECAUTIONS:
- Understanding that if the seat belt sign are left on for a prolonged period of time, it loses it effectiveness for passengers and cabin crew. Use the seat belt sign judiciously.
- Timely notification of anticipated turbulence if possible. This would help facilitate the time required to for the cabin crew to prepare the cabin and allow passenger to return to their seats.
- Timely Passenger Announcements
References
1. Turbulence. Retrieved 18 September 2010, from http://www.skybrary.aero/index.php/Turbulence.
2. Turbulence, Staying Safe. (August 2009). Retrieved 18 september 2010, from http://www.faa.gov/passengers/fly_safe/turbulence/.
3. LEVIN Alan (2010). Turbulence a top cause of midair injuries.USA Today 2010-07-22. Retrieved 18 September 2010, from http://www.usatoday.com/news/nation/2010-07-22-turbulence22_ST_N.htm.
Want to know more?
Sybrary: http://www.skybrary.aero/index.php/Turbulence
FAA: http://www.faa.gov/passengers/fly_safe/turbulence/.
