Injuries aboard airplanes from turbulence are on the decline, thanks partly to new technology, aggressive use of seat belts and an unintended consequence of post-Sept. 11 security concerns.

Last year, no airline passenger in the U.S. suffered a serious or even a minor injury from turbulence in the U.S., according to the Federal Aviation Administration. There have been no passenger injuries so far this year in the U.S. through mid-April, the FAA says.

Eight flight attendants did suffer serious injury last year -- typically broken ankles, the FAA says. That was considerably better than 2003, when 18 flight attendants and three passengers suffered serious injuries. In addition, five flight attendants and four passengers had minor injuries from turbulence in 2003.

In all, eight total injuries in 2004 made it the best year in a decade for avoiding injuries from turbulence, according to the FAA. In 1999 and 2000, turbulence injured more than 90 passengers and crew in the U.S.

The FAA credits the recent U.S. reduction to a combination of increased seat-belt use, better crew training and better weather forecasting. Post-2001 security concerns probably play a big part as well in preventing injuries -- since passengers aren't allowed to congregate in aircraft galleys and sometimes even get shooed back to seats when waiting in line for a bathroom. It's the silver lining to the airline-seat lockdown.

Some injuries can be serious. In March, an EVA Air A330 from Taiwan flew into turbulence near Tokyo that injured 48 people, one with a broken neck. Police said passengers not buckled up were thrown out of their seats, damaging the plane's ceiling. In 1997, a Japanese woman was killed when a United Airlines 747 flying between Tokyo and Honolulu encountered clear-air turbulence and rocked violently. Her seat belt wasn't buckled; 63 others were injured as well.

On average, 58 passengers a year are hurt in the U.S., according to researchers at the National Aeronautics and Space Administration, making rough air the leading cause of injury to passengers and flight crews in nonfatal accidents. Almost all of the injuries can be prevented when seat belts are fastened.

But the improvement comes from more than just buckling up. Northwest Airlines has been a pioneer in developing forecasting for turbulence and wind shear, and today Northwest sells its daily "turbulence plot" to several other airlines. Northwest is particularly interested in the issue because it flies so much in mountainous areas. The information comes in the form of maps as well as instant text messaging sent to pilots in the air. Pilots can get warnings of turbulent air hundreds of miles in advance through onboard computers, or from FAA air-traffic controllers who collect reports of bumpy rides from planes, and figure out which altitudes are smoother than others.

Starting earlier this year, pilots and air-traffic controllers have more flexibility to try to avoid pockets of turbulence because the FAA doubled the number of available altitudes jets can use when cruising, in order to boost airspace capacity. Equipped with more accurate altimeters, jets can now cruise 1,000 feet apart vertically, instead of 2,000 feet. That opens up more opportunity for pilots to find smoother air, perhaps just 1,000 feet higher.

To a meteorologist, turbulence is an irregular or disturbed flow in the atmosphere, much like waves on an ocean, produced when cold air collides with warm air or tall mountains disrupt the flow of air. Gusts and eddies can spin off the edges of the jet stream, and the invisible wind waves create "clear air turbulence" that can catch aircraft without warning. When wind currents change speed and direction, it affects the lift produced by an airplane's wings. With a shift, a plane can suddenly drop a bit, or bounce up.

For passengers unsettled by the stomach-churning drops from wind shear, it's important to remember that there's still plenty of air underneath the plane and the aircraft isn't going to fall out of the sky. What's more, airplanes are designed to withstand incredible forces far beyond what they encounter even in the most violent turbulence. In clear-air turbulence incidents, injuries result from passengers and crew not being buckled into their seats, not from damage to the airplane.

If your stomach gets queasy from the lurches of a rough ride, two tips: First, people in the back of the plane are more vulnerable to gyrations than people near the cockpit, especially on long planes like the Boeing 757. Second, looking out the window helps many people overcome the queasiness. (The horizon and other stable landmarks provide a frame of reference to help balance your body.) However, looking down at your lap will make you only more disoriented.

Of course, the best ride comes from smooth air. And the better airlines get at flying through smooth air, the safer we'll be.

Researchers say new advances are coming that should help smooth out flights more. NASA is currently testing a radar device on a Delta Air Lines 737-800 that measures wind flows instead of rain. The test, which began last June and runs to Sept. 30 has already correctly predicted turbulence encounters 300 times, NASA says.

The equipment, called Turbulence Prediction and Warning System, or TPAWS, is actually a software and hardware upgrade to the plane's wind-shear predictor, which gives pilots a warning of wind-current changes at low altitudes around airports. The new version, built by Rockwell Collins, "sees lots of things that regular radar doesn't see," says NASA's Kathy Barnstorff.

With even just a few minutes of warning, planes can fly around pockets of turbulence, or pilots can get passengers seated and buckled up.

In addition, NASA is testing a new automated turbulence-reporting system on more than 70 Delta planes. When a plane encounters turbulence, a precise message is sent to the ground and shared with airline route planners, air traffic controllers and other pilots.

Delta says the new technology has not only helped planes avoid turbulence, but also allowed planes to make better use of air space because of more accurate charting of turbulent air. That should both reduce air-travel congestion, and allow pilots to reduce how often they turn on the seat-belt sign to strap down passengers.

"With these tools, we'll have better knowledge of where turbulence is and we won't cry wolf as much," said Bill Watts, the turbulence program manager for Delta. "We can get people to sit down when they really need to sit down."