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Don Paul: How engineers help you fly safely

Recently I wrote an article on the role of meteorologists in aviation safety.

I discussed one hazard known as clear air turbulence, or CAT. CAT is the biggest cause of in-flight injuries in civil aviation. CAT is essentially invisible both on radar and to the cockpit crews’ eyes.

There are geographical regions which are known to be more commonly associated with CAT, such as the turbulence produced by strong upper level winds intersecting mountain ridges, especially ridges perpendicular to the winds. Airline pilots and most general aviators have been trained to be alert for this more common turbulence, often found east of the Sierra and Rockies ranges at somewhat lower altitudes.

Higher up, CAT becomes more difficult for aviation meteorologists to forecast in atmospheric layers where the primary source of turbulence isn’t associated with detectable clouds and storms, but invisible intersecting winds.

Where intersections are occurring, wind shear will result. Wind shear is any sudden change in wind speed or direction. Strong shear can produce highly disruptive changes in an aircraft’s pitch, yaw and lift. The shear can be severe and occasionally extreme. Aircraft are engineered to withstand even extreme turbulence. But unsecured passengers, flight crew and serving carts can become upwardly mobile projectiles, tossed violently if a plane suddenly has lost lift and quickly loses altitude as a result. The lack of warning for much CAT is the reason passengers should always be securely belted when seated, even if the flight is smooth at a given moment.

The invisible “cloaking” is beginning to change. Work pioneered by engineers and electronics specialists at the Japan Aerospace Exploration Agency has been progressing in using what is known as LIDAR in detecting CAT close ahead in an aircraft’s path. LIDAR stands for Light Detection and Ranging, in which a pulsed laser beam is sent out and, in a sense, illuminates a target for a three-dimensional image which is measured through the reflected image of the laser pulses. What’s the target if CAT is unseen? Aerosols, such as water vapor and tiny dust particles are visible to the LIDAR if close enough to the aircraft. The LIDAR imagery can detect vertical and horizontal motion of the aerosols and mathematical algorithms can translate this imagery into mapped air currents, much as does Doppler radar with more visible targets in precipitation.

With this LIDAR information, pilots can reduce speed and alter control surfaces to reduce exposure to the CAT, and they can alert passengers and flight attendants to quickly seat themselves and buckle up for safety. This JAXA video illustrates the difference in safety advance warning of CAT can make for the aircraft, and those in the cabin.

CAT also sometimes occurs at critically low altitudes, affecting final approaches and landings. The LIDAR warning technology also will give pilots more opportunity to ready themselves and their craft’s control surfaces for this hazard, and a better chance to execute a safe “go around” to avoid the wind shear and attempt another, safer landing.

With Doppler LIDAR, lower altitude CAT is more readily detectable because aerosols are larger and more concentrated than at high altitudes. For higher altitudes, more powerful LIDAR systems are necessary to reach the smaller, more thinly scattered aerosol targets. These systems are now coming out of research, and forward range detection has been increasing. With these new LIDAR applications, U.S. aviation giant Boeing has joined in with the Japanese agency and is scheduling test flights on larger aircraft later this year. The latest version of this technology has demonstrated a range out to 17.5 kilometers in front of the aircraft, giving the cockpit crew enough time to alert passengers to the rapidly approaching hazard. To go with the LIDAR system, new aircraft control response systems are being engineered to immediately alter control surfaces such as ailerons to reduce vulnerability to the turbulence.

Pilots routinely report encounters with significant turbulence. These PIREPS are extremely valuable to cockpit crews and Air Traffic Control in mapping out nasty turbulence already in progress. New, easy-to-use laptop mapping applications with virtually instantaneous display of PIREPS are already affording pilots more timely information on turbulence zones for both small and large geographical scales. These high-tech communications breakthroughs from private enterprise are adding to the arsenal against CAT and other types of turbulence.

Things will be looking up for nervous fliers in the sky monitoring their white knuckles. Another notch for in-flight safety is being carved.

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