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Editor’s Note: Seeking the Delicate Balance

By David Jensen | June 1, 2000
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Where is the delicate balance?

The digitized cockpit could grant air crewmen virtually an endless amount of flight-critical data. But such a capacity fosters the concern of creating confusion among pilots from information overload.

And greater situational awareness in the cockpit allows air crewmen to play a larger role in decision-making–stepping closer into the realm of Free Flight, if you will. But that begs the question, where does the pilots’ responsibility end and the air traffic controllers’ begin?

Amy Pritchett, professor at the Georgia Institute of Technology, is well aware of the fragile balance being weighed as the aviation industry seeks new ways to safely accommodate more and more air traffic. That’s why when she speaks of the results of a one-year study she conducted for the National Aeronautics and Space Administration (NASA), she is quite attempted to begin her talks with an emphatic: "This is NOT self separation!"

What is the topic of Pritchett’s research?

As you might guess, it involves the separation of aircraft as they enter the terminal control area and make their approach to land at a major airport. Specifically, her study–the results of which are to be presented to NASA this month–pertain to the use of an enhanced cockpit display of traffic information (CDTI). This display would make air transport pilots more aware of traffic flow so that they can better judge their separation from other aircraft when making an approach to a busy, major airport.

Twelve airline pilots assisted in the study, utilizing the CDTI while "flying" in a flight simulator. The participants’ experience level ranged from B727 copilots to captains on new widebodies. The simulations, which were completed early last year, were to ascertain the level at which pilots felt comfortable with the amount of data received. Again, avoiding information overload.

Primarily, the information on the display would have "ADS-B quality," according to Pritchett. "It would be larger and much clearer than TCAS [traffic alert and collision avoidance system] displays."

Additional information was provided on the standard terminal arrival route (STAR) charts used by the pilots–more information than just altitude and waypoints to follow.

"We added expected speeds for an approach," says Pritchett. But these speeds were just starting points; for some simulations, additional information such as settings from the lead aircraft’s autopilot also were added to the CDTI. With such information, plus knowledge of wind conditions, air crewmen can better judge their spacing with lead aircraft and "tighten up" when lining up for the approach, Pritchett says.

"Controllers aren’t aware of wind conditions and don’t know the aircraft’s acceleration profile, so they get conservative and may put in a buffer between aircraft," Pritchett explains. "But if pilots know what’s ahead, they won’t need the buffer and will tighten up traffic."

Beginning to sound like self separation? Not at all, says the Georgia Tech professor. The CDTI "would allow controllers to give higher types of commands and communicate more directly with pilots," she contends. Pritchett adds that controllers and pilots would have less voice communication but more information would be transmitted during each audio contact. The controller would be freed of low-level commands–"turn right," "turn left" etc.–and could give instructions such as, "Follow aircraft N1234 at eight miles."

"On average, a controller gives 11 commands [during an approach], but with the CDTI, he or she may have to give just three or four commands, but each command will be of a higher level and give more information," says Pritchett. "So CDTI could help reduce voice communication congestion."

Of course, controllers must always maintain their traffic monitoring duties. Not all pilots might have a CDTI or be using one when entering an arrival route. They will need either conventional instruction or a reminder to turn on and utilize the display.

What did the pilots in the experiment think of CDTI? "Eleven out the 12 pilots thought CDTI is the way to go," says Pritchett. "One pilot said, ‘I’m happy having no more responsibility.’ Support for the CDTI was strong but not unanimous."

Regarding the amount of data received, the pilots "didn’t feel comfortable performing in-trail spacing until they knew the speed of the lead aircraft," Pritchett adds. Better yet, they wanted to view the target speed dialed into the lead aircraft’s autopilot.

One so-called "off-nominal event" did generate pilot concern. During one simulation, the lead aircraft backed off its airspeed 50 knots more than expected. "The pilots found this hard to deal with [while using the CDTI] and they wanted the controllers to intervene, to tell the aircraft’s crew to speed up or tell them they’re not doing their job."

The Cargo Airline Association (CAA) is keenly interested in CDTI, as it is akin to the automatic dependent surveillance-broadcast evaluations it has conducted. Pritchett has had contact with the CAA and spoke before the RTCA and officials of the Federal Aviation Administration. She also is scheduled to speak at the Aviation 2000 Conference and Exhibition that Avionics Magazine will sponsor Oct. 28-Nov. 1. Her work joins that of others who seek the delicate balance that will deliver both efficiency and safety to future flight operations.

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