Thirty years ago, Hartsfield-Jackson Atlanta International Airport’s air traffic controllers assigned departure headings at their discretion. This practice made it very difficult for residents or potential residents near the airport to gauge typical aircraft noise impacts or to understand what a typical day’s flight activity relative to their location might be. In 1972, a task force was convened to formulate a process that would concentrate aircraft departures—and the noise they produce—over less noise-sensitive areas. We call the preferred flight path a “noise abatement departure track” (NADT), and we refer to less noise-sensitive areas as compatible land-uses. Representatives from the communities surrounding the airport, the FAA, and the City of Atlanta/Department of Aviation were on the team that created the tracks.

Only jets must conform to the tracks, as other types of airplanes are inherently quieter than they are. Another reason that non-jets don’t use the NADTs is that they would get in the way of the better performing jets and begin to make the NADTs burdensome to controllers and pilots.

What principles does the FAA use to keep an airplane on a NADT? A specialist called the Local Controller issues the pilot of the airplane either a no-wind or a wind-corrected heading designed to achieve conformity with the idealized NADT and instructs the pilot to turn to that heading at a location known as the middle marker. The Local controller then tells the pilot to contact the Departure Controller. After turning to the NADT heading, the airplane will normally stay on that heading until either one of two conditions is met: 1) the airplane reaches an altitude of 5,000’ MSL (mean sea level); or 2) the airplane travels a distance of 5 NM (nautical miles) or more from the end of the runway it departed off of. After fulfilling one of those conditions, the Departure Controller will contact the pilot and vector (issue turning instructions) the airplane towards its departure gate.

The NADTs create very desirable consistency, but there are limits to how closely airplanes can follow the ideal track. Pilots and controllers cannot coordinate their actions—as hard as they may try—to fly the NADT as accurately as a car can drive within a certain lane of traffic. Current navigational procedures are not yet sophisticated enough for that to be possible. Nevertheless, if the average person were to examine pictures of HAIA flight tracks from different days of the same operational flow it would be surprising if he or she could discern any major differences between the days. Even the average altitudes of airplanes using the corridors are fairly constant relative to the areas they typically fly over. You might notice that airplanes are lower over a given area when it is hot, however, since climb rates tend to suffer with an increase in temperature and humidity.

Right now, the NOMS Program is working on ways to ensure that airplanes better adhere to our noise abatement tracks. We send a daily NADT deviation report to the Air Traffic manager’s office at the TRACON. We’ve revised pilot departure charts to codify existing NADT procedures; a special brochure will soon highlight the importance of flying the track accurately. We are working with the FAA and an airline to accelerate the implementation of RNAV SIDs (standard instrument departures). This may allow aircraft to turn to the heading assigned by an air traffic controller at a more precise location, which would result in a more concentrated departure corridor. Airplanes capable of flying RNAV routes have special devices called FMSs that act like the cruise control on your car. The FMS can more precisely fly a track than the pilot can using conventional navigation and equipment.

Soon, the FAA will modify westerly flow NADTs to accommodate the fifth runway. The same principles that have governed the existing NADTs will apply to both the modified NADTs and the new NADTs created for the fifth runway.