Reader Feedback: Regarding Boeing Tailored Arrivals

Regarding our report of Boeing Tailored Arrivals, Reader Lou Rosgen wrote: "I recall this same program at Denver Stapleton, as well as several others.  'Profile Descent' was the name of the program, even had published procedures.  Are we reinventing the wheel here?"

Editor's Response:

There was a prior "profile descent" program that included Denver.  However, the "tailored arrivals" of today might be more aptly described as wheel improvements rather than wheel reinventions.

Mr. Rosgen's recall of "profile descents" is likely referring to the FAA's LFM/PD (local flow management/profile descent), which according to a NASA document (Airborne Trailblazer, Chapter 7-1), was first installed on an experimental basis at Denver and Dallas Fort Worth in the late 1970s.

While LFM/PD was considered an improvement over existing arrival procedures, it had a couple of significant drawbacks:  First, while the program gave the controllers the time each aircraft was to cross its metering fix, they had to manually compute how to get the airplanes to that fix at the correct time, speed, and altitude.  Second, even though pilots were given the speed and altitude, or altitude range, at which they were to cross the fix, controllers had the responsibility for modifying the speed and/or descent profiles of arriving aircraft to meet the time requirements of the schedule.

In the late 1970s, researchers at Boeing and NASA began working on profile descent equations, using the four-dimensional capabilities of NASA's TSRV (transport systems research vehicle) 737's FMS (flight management system).

In June 1979, these new algorithms were installed in the TSRV 737, for a series of flight tests of LFM/PD at Denver, which proved to be successful, and the FMS-controlled profile descent proved to use 28% less fuel.

But there were other issues:  For example, what would be the consequences of different airplanes using different, climb and descent paths and speed profiles even though they made their metering fix times?  And how would aircraft using profile descents mix with aircraft not equipped for that kind of approach?  In addition, even though the airborne FMS was capable of accuracies within seven seconds, the ground metering system at that time was only accurate within 30 seconds.

NASA conducted additional profile descent experiments in 1984-85, which eventually showed that if individual airplanes were controlling their own descent paths, controllers wouldn't be able to predict the exact trajectory of the descending airplanes, and there was too much potential for unexpected maneuvers.  In other words, even though the onboard technology worked well, the ATC infrastructure couldn't incorporate it.

It wasn't until the FAA began introducing CTAS (center tracon automation system), in the l990's that controllers had the same basic information that pilots had that things could move forward.  Denver and Dallas-Fort Worth were two of the first airports to get this arrival tool.

The oceanic tailored arrivals (OTA) of today use the integrated CNS (communication, navigation, and surveillance) capabilities available in aircraft with FANS (future air navigation system) equipment, and the ground capability available through the FAA's ATOP (advanced technologies and oceanic procedures) system.  ATOP, which is also known as Ocean 21, is currently in various stages of deployment at the Oakland, New York and Anchorage ARTCCs (air-route traffic control centers).

A number of flight demonstration activities associated with Tailored Arrivals have been carried out in the U.S and abroad. An in-service demonstration was conducted by Airservices Australia in 2004, in partnership with Qantas Airlines, Boeing and the Air Traffic Alliance, where static clearances were issued by datalink to B-747 and A-330 aircraft into Melbourne and Sydney.  Other related activities include continuous descent approach (CDA) field trials conducted at Louisville in 2002 and 2004 with United Parcel Service, and similar CDA trials at Mather airport near Sacramento, and RNAV (area navigation) arrivals into Atlanta.  Other important related work is going on in Sweden, where in January of this year, a SAS B-737 performed, what was described as the first managed four-dimensional-trajectory (4DT) flight, as well as the first advanced continuous descent approach (A-CDA), ever made in revenue service.  10-10-2006.

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