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The DC-8 lost its left outboard engine and 19 feet of wing and fell 500 feet in 10 seconds, but landed safely. (NCAR)

The Calculators of Calm

Just how far out of their way will airlines go to give you a smooth ride?

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(Continued from page 3)

“In reality, I think all [airlines are] doing is trying to have a more reliable, robust seat belt warning light, basically to get people buckled down, and to secure the cabin with enough advance warning,” says Hannon.

The Doppler upgrade is closer to deployment than lidar, but both should give pilots and crews about 90 seconds of warning. NASA staff scientist Rod Bogue, a former manager of TPAWS, says that, based on recent experiments conducted on the length of time it takes to get passengers and flight attendants seated and buckled, 90 seconds is just about the right amount of time.

Another promising technology unrelated to TPAWS is the use of Next Generation Radar—a nationwide network of extremely powerful and sensitive Doppler radars—to detect turbulence. The National Weather Service, NOAA, the U.S. Air Force and Navy, and the FAA operate nearly 160 NEXRAD radars. Cornman is confident that the FAA will fund an NCAR project for this year in which NEXRAD data from around Chicago will be quickly posted online for United’s dispatchers and meteorologists. “The other aspect of the program that we’re also talking to United about is to uplink this data to the cockpit,” says Cornman. Printers in the cockpit could spit out alerts that would inform pilots about turbulent conditions along their approach paths.

“Basically we tell our students that whenever possible, just avoid turbulence,” says Mike Corradi, chief flight instructor at Embry-Riddle. “That way, you’ll never have to prove your superior talents as a pilot.”

Even moderate turbulence poses unwelcome piloting challenges, a point made soberingly clear when Corradi straps me into the left seat of a flight training device. Unlike a flight simulator, the device doesn’t mimic the sensation of motion, but the 220-degree wrap-around screen showing computer-generated flight in real time provides an extremely realistic illusion of it.

After a relatively smooth takeoff, I level off at 8,000 feet, gazing at the detailed scene around and “below” me. The instruments on my control panel are all steady, calm, and easy to read. Then Corradi switches on the turbulence input, dialing up to 3 on a scale going up to 10. The horizon starts to bounce, pitch, roll. My instruments—when I can read them—indicate constant yawing. The scenery dances. It’s all I can do just to maintain a semblance of level flight, which gradually slips from my grasp as I try to right the aircraft according to the instruments. Finally Corradi freezes the screen image and tells me to look up, saying, “Now, this is a picture you never want to see.” I’m locked in a bank of more than 30 degrees, a mountain range is at eye level and about a mile dead in front, and I’ve been steadily losing altitude.

I’m not a pilot—and the flight training device is simulating a small aircraft—but it’s not much easier for professionals flying big jets. “I can tell you, it’s very fatiguing to be in turbulence for a long period of time,” says Terry McVenes, an Airbus A320 pilot for U.S. Airways. Fatigue can undermine concentration, and in areas of high turbulence, pilots must constantly be at the controls; a good jolt to the aircraft can disengage an autopilot system. More recent and sophisticated autopilot systems can handle it, but many pilots prefer to fly manually through turbulence because it gives them a better sense of control.

When a flight hits turbulence that is moderate or worse, pilots follow certain procedures and then pursue options. First, they turn on the seat belt sign in the cabin, perhaps even make an announcement. Then they slow the aircraft down, just as a driver brakes when hitting a bumpy road. “All aircraft have a turbulence penetration speed,” McVenes says, referring to a manufacturer’s recommendation of an optimal speed for flying through bad air. “If you’re in the passenger cabin, you’ll hear the engines back down.”

After alerting the cabin, says Hank Krakowski, a veteran pilot for United, “I talk to air traffic control to see what they know about turbulence in the area and if changing altitude makes sense.” Air traffic control usually has some knowledge of any recent reports about turbulence at various altitudes. If the turbulence is on the downwind side of a thunderstorm, Krakowski, per United policy, has to double the wind speed at his altitude to determine the number of miles he must keep between him and the storm. For instance, if the wind speed is 23 miles per hour, he must fly at least 40 miles away from the lee side of the storm. “Once I’ve gotten into smooth air,” Krakowski says, “I then let United dispatch know I’ve changed altitude and then see the effect it’s going to have on my fuel.”

In other words, the numbers game begins again. If the lower altitude is going to eat up so much fuel that Krakowski may find himself in a dangerous situation should he have to enter a hold at his destination—or worse, have to divert—he may later climb back up and stay there, provided the turbulence is not severe. “While you want to create a great experience for the customer, the most important thing we do for them is get them to their destination and connections on time,” he says. “So sometimes they have to live, as we do, with the foibles of the atmosphere.”

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