Turbulence! Strap yourself in.

Turbulence is air movement that normally can not be seen and often occurs unexpectedly. It can be created by a number of different conditions, including atmospheric pressures, jet streams, mountain waves, cold or warm fronts, and thunderstorms. Turbulence can happen even when the sky appears to be clear.

In the aftermath of two serious turbulence events in 1995, the Federal Aviation Administration issued a public advisory to airlines urging that passengers use seat belts at all times. The FAA concluded that the rules concerning seat belts did not require strengthening, but that a public education initiative was necessary to encourage their usage. Current FM regulations require passengers to be seated with their seat belts properly fastened when the aircraft leaves the gate and until it climbs after takeoff; during landing until the aircraft reaches the gate and comes to a complete stop; and whenever the seat belt sign is illuminated during flight.

Statistics back up the need for precautions:

* In non-fatal accidents, in-flight turbulence is the leading cause...