Many passengers do not understand the effects of turbulence, or that an encounter with turbulence may occur without warning.
What is turbulence?
Turbulence is air movement that normally cannot be seen. It may occur when the sky appears to be clear and can happen unexpectedly. It can be created by any number of different conditions, including atmospheric pressures, jet streams, mountain waves, cold or warm fronts, or thunderstorms.
Different intensities of turbulence
Light turbulence - briefly causes slight, erratic changes in altitude and/or attitude.
Light chop - slight, rapid and somewhat rhythmic bumpiness without noticeable changes in altitude or attitude.
Moderate turbulence - similar to light turbulence, but greater intensity. Changes in altitude/attitude occur. Aircraft remains in control at all times. Variations in indicated air speed.
Moderate chop - similar to light chop, but greater intensity. Rapid bumps or jolts without obvious changes in altitude or attitude.
Severe turbulence - large, abrupt changes in altitude/attitude. Large variation in indicated airspeed. Aircraft may be temporarily out of control.
Extreme turbulence - aircraft is violently tossed about and is impossible to control. May cause structural damage.
The reactions inside aircraft vary from occupants feeling slight strain against their seat belts and unsecured items being slightly displaced, through to occupants being forced violently against seat-belts, and unsecured items being being tossed about. (Imagine what it would be like if you were not wearing a seat belt!)
Clear air turbulence
There are several notable problems with clear air turbulence:
- It cannot always be foreseen so there is no warning.
- It is usually felt at its mildest in the flight deck and is generally more severe in the aft section.
- It can occur when no clouds are visible.
- Aircraft radars can't detect it.
- It is common at high altitudes, where cruising airline suddenly enter turbulent areas.
Turbulence is the leading cause of in-flight injuries. There are countless reports of occupants who were seriously injured while moving about the passenger cabin when clear air turbulence is encountered.
- Thermals - Heat from the sun makes warm air masses rise and cold ones sink.
- Jet streams - Fast, high-altitude air currents shift, disturbing the air nearby.
- Mountains - Air passes over mountains and causes turbulence as it flows above the air on the other side.
- Wake turbulence - Near the ground a passing plane or helicopter sets up small, chaotic air currents, or
Microbursts - A storm or a passing aircraft stirs up a strong downdraft close to the ground.
In-flight turbulence is the leading cause of injuries to passengers and crew. Occupants injured during turbulence are usually not wearing seatbelts, ignoring recommendations to keep seatbelts fastened even when the signs are not illuminated. It is recognised that passengers need to move around the cabin to use restroom facilities or to exercise on long flights. However you should keep your seatbelt fastened at all times when seated.
From 1981 through 1997 there were 342 reports of turbulence affecting major air carriers. Three passengers died, two of these fatalities were not wearing their seat belt while the sign was on. 80 suffered serious injuries, 73 of these passengers were also not wearing their seat belts.
Turbulence related incidents
The following are recent jet airliner mishaps from around the world. In each event, at least one passenger/flight attendant was injured during an unexpected turbulence encounter.
- During a flight from Singapore to Sydney with 236 passengers and 16 crew, the airplane encountered turbulence over central Australia. The plane hit an "air pocket" which caused it to drop 300 feet. Nine passengers including one pregnant woman and three crew members suffered various neck, back and hip injuries, with one of the passengers requiring surgery. Those who were injured were not wearing seat belts.
- During a flight from Japan to Brisbane 16 passengers were injured when a large aircraft encountered turbulence. Passengers had been advised to keep their seatbelts fastened while seated. The pilot in command reported that flight conditions were smooth prior to encountering the turbulence. The weather radar did not indicate adverse weather, so the crew did not turn on the seatbelt signs. A number of the passengers who were not wearing their seatbelts were injured when they were thrown from their seats.
- A jet hit air turbulence shortly before it landed at a Hong Kong airport, injuring 47 people, seven of them seriously. "It happened very suddenly and everything was very chaotic," one of the 160 passengers aboard the flight said. "The plane just dropped and I saw things flying all over."
For more information on turbulence read the Australian Transport Safety Bureau's Staying safe against in-flight turbulence fact sheet.