High-End GPS May Give Airline Passengers Smoother Flights

As reported by Forbes: Anyone who’s flown can attest to atmospheric turbulence. My worst was one late December in the North Pacific, some 400 miles south of the Aleutians. The plane started shuddering and bucking so badly that even the flight attendants looked spooked.

But moderate to severe turbulence can cause more than just a racing heart.

Passengers aboard two recent flights encountered severe, if not extreme, clear air turbulence. The first incident, in which five United passengers and crew were injured, took place earlier last month as a Boeing 737 was making its approach into Billings, Montana.

The second, a day later, took place aboard a Cathay Pacific Boeing 747 en route from San Francisco to Hong Kong. Several passengers and crew were injured in some thirty seconds of severe turbulence over the Japanese Island of Hokkaido, which at least one passenger described as nothing short of a “roller coaster.”

In fact, the FAA (Federal Aviation Administration) reports that there are more than 1000 turbulence-related injuries on commercial aircraft each year. In the last decade alone, Robert Sharman, an atmospheric scientist at NCAR (National Center for Atmospheric Research) in Boulder, Colorado, says there have even been a handful of turbulence-related deaths.

But atmospheric weather at a range of altitudes is inherently harder to predict than surface weather.

“The difficulty is that turbulence is highly spatially dependent and can change in ten minutes’ time,” said Sharman. As a result, he says, most turbulence alerts still originate from the pilots themselves.

However, Seth Gutman, an atmospheric scientist at NOAA (National Oceanic and Atmospheric Administration) in Boulder, and colleagues, has proposed using the existing Global Positioning System (GPS) as a real time probe for atmospheric turbulence.

GPS signals, Gutman explains, are refracted and delayed by water vapor as they travel through earth’s lower atmosphere.

“We take that signal delay info and provide that to weather models,” said Gutman. “But instead of averaging this out over half an hour, we propose doing it over timescales of about a second.”

The key is tapping into existing state-of-the-art GPS receivers that are typically used for high-accuracy applications; including emergency response; engineering; road construction; even geophysics monitoring.

Gutman says there are already thousands of such GPS receiving stations across the U.S. maintained mostly by state and local governments.

The idea is to use arrays of these systems at fixed locations on the ground to directly detect turbulence within the GPS antennas’ field of view.

The same principle would also apply for use with Russia’s Glonass system; Europe’s forthcoming Galileo system; China’s Compass; and Japan’s QZSS.

Such a turbulence warning system could even cover the polar routes, says Gutman.

One potential shortfall of Gutman’s proposal, however, is that although GPS signals can point out turbulence within a specific vertical column, knowing at which altitude in that column is likely to cause problems for passing aircraft would still be difficult to determine.

Although mountains, jet streams, weather fronts and atmospheric convection can all cause clear air turbulence, fortunately, most turbulence is rarely severe.

What does Sharman classify as severe turbulence?

“Either momentary loss of control of the aircraft or a one ‘g’ acceleration,” said Sharman. “That means if you’re not buckled in, you’re flying out of your seat.”

Still, most commercial pilots would argue that severe turbulence rarely lasts more than a few seconds and even though the cockpit may momentarily lose control of the aircraft, once the incident is over, the plane automatically regains its flying composure.

Is a commercial airliner structurally at risk during severe turbulence?

“It can be,” said Sharman. “I've seen pictures of parts of a composite wing coating being ripped off. If you start bending or twisting a wing surface, some of that material can come off.”

In 1992, a DC 8 cargo aircraft suffered turbulence so severe over the Front Range of Colorado’s Rocky Mountains that its left outboard engine was completely ripped off as well as some 12 feet of its left wing’s leading edge. Mercifully, the pilot was able to limp into Denver International.

What can be done to avoid such incidents?

To a large degree, Gutman says it all comes down to national priorities. Gutman asks, do we as a nation want to use such systems to improve our ability to forecast and warn of severe aviation turbulence?

If so, Gutman says the proof of concept for this GPS-related turbulence avoidance system is ripe for the financing.

“If we had resources,” said Gutman, “we could do a demo this summer. Implementation is not difficult. What takes time is verifying that what we’re seeing corresponds to real events, so that false notifications of turbulence are low.”