Federal Aviation Administration

The Duwamish Flight Track study was conducted by the Federal Aviation Administration (FAA) in response to a letter dated July 21, 2000. from the President of the Port of Seattle Commission. That letter requested that the FAA determine the operational feasibility of specific flight track change recommendations, which were, contained in the Port of Seattle (POS) Commission Resolution Number 3401, as amended. The request was for the FAA to maximize the use of the Duwamish/Elliott Bay Corridor, a north-flow left-turn procedure, preferably by assigning that routing to jet departures that today use a north-flow right-turn procedure entitled the SUMMA Departure.

Seattle-Tacoma International Airport is in a north-flow configuration (landing and departing to the north) approximately 35 percent of the year. Direction of landing and departing is largely dependent on wind direction and velocity.

The task set before this workgroup was to determine the feasibility of, and changes required for maximum use of the Duwamish/Elliott Bay Corridor for aircraft departing to the north. The goal of the group was to determine the operational feasibility of each alternative and to conduct analysis of the impacts of increases to curfew hours.

A number of alternatives were explored. The majority of the alternatives reflect the proven air traffic control concept of resolving major flow crossovers in the terminal environment below 10000 feet Mean Sea Level (MSL). This is a major design factor in the Four-Post terminal configuration. The Four-Post terminal concept, as employed at Seattle, is also found in the terminal airspace at Denver, Los Angeles, Atlanta, Chicago, San Francisco, Dallas-Fort Worth, and most major terminals across the country.

Alternative re-routes studied by the workgroup were designed to connect with the appropriate established en route flows and to be compatible with the existing Seattle TRACON (Terminal Radar Approach Control) Four-Post configuration. The relocation of other major Seattle TRACON flows was not considered within the scope of this study. Additionally, changes to national traffic flows and en route sectorization are being addressed through the National Airspace Redesign effort and changes of that magnitude are beyond the scope of this study.

The Sector Design Analysis Tool (SDAT), an automated modeling tool that assists in the design of traffic flows, was used to depict baseline and possible alternative routes and explored the potential operational impacts of each. Experiential analysis methods were also employed to augment the process when the limitations of the modeling tool were reached. Senior A»r Traffic Control personnel, with extensive experience in both en route and terminal operations, supplied the human expertise necessary for realistic model development.

The first alternative considered (Study Alternative #1) was to re-route all aircraft today assigned the SUMMA Departure procedure via the Duwamish/Elliott Bay flow until west of the southbound arrival flow (downwind) over Elliott Bay. At that time the aircraft would be given climb instructions and turned southwest along the route of the San Francisco/Honolulu/Portland traffic. When these aircraft are above the arrival traffic inbound from the south and southwest they would be turned south/south eastbound to intercept the Seattle VORTAC (Note 1) 143-degree radial, proceed to the SUMMA intersection on course to continue their flight plan route.

The analysis of this option indicates restrictions for traffic such as stopping the climb or vectoring an aircraft north of Elliott Bay would be used in order to maintain the current level of safety. Although by definition this alternative is operationally feasible the analysis shows the accumulative negative impacts of such action. Traffic Management System restrictions would need to be employed to alleviate the additional conflicts and increased coordination requirements. A significant increase in departure delays during high traffic demand periods or during periods of low visibility would occur thus reducing efficiency well below current levels.

The second alternative considered (Study Alternative #2) was to re-route all aircraft that are today assigned the SUMMA Departure procedure via the Duwamish/Elliott Bay flow until nearing the western opening of Elliott Bay. At that time the aircraft would be given a sharp left turn direct to the Seattle VORTAC, creating a teardrop pattern, thence via the Seattle VORTAC143 radial to SUMMA intersection, then continue on their flight plan route. Each aircraft could remain altitude restricted until back west of the southbound arrival flow (downwind) over Elliott Bay, and would then have to climb to be above the arrival traffic operating east and southeast of Seattle.

The analysis of this option presents the highest level of safety concern. Severe restrictions would need to be imposed in order to maintain the current level of safety and to alleviate the additional conflicts and increased coordination requirements. A significant increase in departure delays during high traffic demand periods or during periods of low visibility would occur resulting in reduced efficiency. The workgroup found this alternative is not operationally feasible.

The third alternative (Study Alternative #3) considered was to re-route only one of the two traffic flows that use the SUMMA Departure procedure. Those that are destined for cities southeast of Seattle (i.e., Atlanta, Dallas-Fort Worth, etc.) would not be re-routed. These would continue to be assigned the SUMMA Departure procedure with a transition route over Baker City, Oregon. Those aircraft destined for the Los Angeles Basin and Southwest U.S. cities would be re-routed via the Duwamish/Elliott Bay Corridor. Then (as in the first alternative), when these aircraft are west of the southbound arrival flow (downwind) over Elliott Bay, they would be given climb instructions and turned southwest along the route of the San Francisco/Honolulu/Portland traffic. When above the arrival traffic inbound from the south and southwest they would be turned south/south eastbound to parallel the Seattle VORTAC 143-degree radial, until south of the SUMMA intersection and then routed direct Lakeview, Oregon or given a heading to intercept and proceed via the 143-degree radial, on course to continue their flight plan route.

Although by definition this alternative is operationally feasible the analysis shows the accumulative negative impacts of such action. The analysis of this option indicates restrictions would need to be imposed in order to maintain the current level of safety and to alleviate the additional conflicts and increased coordination requirements. A significant increase in departure delays during high traffic demand periods or during periods of low visibility would occur resultingin lower efficiency than currently exists.

The fourth alternative (Study Alternative #4) was to re-route all aircraft that are today assigned the SUMMA Departure procedure, via the Duwamish/Elliott Bay flow until west of the southbound arrival flow (downwind) over Elliott Bay. At that time the aircraft would be given climb instructions and turned southwest along the route of the San Francisco/Honolulu/Portland traffic. Aircraft destined for points southeast, would be routed over Baker City, Oregon as described in Alternative #1. Aircraft destined for the Los Angeles Basin and vicinity, would continue within the existing San Francisco flows, passing northwest of Olympia, Washington and turning southbound direct to Eugene or Corvallis, Oregon. At that point, the Los Angeles traffic would be routed to cross the major West Coast northbound routes to get to Lakeview, Oregon to join the existing Jet Route flows.

The workgroup did not evaluate routes which would enter and transit Oakland ARTCC and/or Los Angeles ARTCC airspace on routes other those in use today. Realignment of, and/or establishment of new routes which go beyond an individual facility's airspace and jurisdiction fall under the purview of the National Airspace Redesign (NAR) effort and are beyond the scope of a Regional Office or facility to approve. Analysis of impacts would depend upon the specific route(s) determined by the NAR efforts with all involved facilities.

The analysis of this option indicates a significant mileage increase for aircraft assigned this alternative routing. The analysis also indicates restrictions for traffic such as stopping the climb or vectoring an aircraft north of Elliott Bay would be used in order to maintain the current level of safety. Traffic Management System restrictions would need to be employed to alleviate the additional conflicts and increased coordination requirements. A significant increase in departure delays during high traffic demand periods or during periods of low visibility would occur thus reducing efficiency well below current levels in the TRACON operation. Additionally, this alternative would create conflict and cross over situations in the en route environment that mirror those which were eliminated by the implementation of the "Four-Post" plan in 1990. Although by definition this alternative is operationally feasible the analysis shows accumulative negative impacts in increased delays and mileages and route conflicts. Changes that would affect Oakland and/or Los Angeles ARTCC's or mandate changes to established west coast flows could not be addressed by this work group.

The study found that Alternatives #1, #3, and #4 are by definition operationally feasible, meaning that the re-routes, as described, can be safely accomplished by Air Traffic Control. However, it must be recognized that each of these alternatives, if adopted, would noticeably impact the operational capabilities of Seattle TRACON and would adversely impact the efficiency of Seattle-Tacoma International Airport and other airports within TRACON airspace. The adoption of any of these alternatives would result in a significant increase in departure flow restrictions to maintain the current level of safety and alleviate the additional conflicts and increased coordination requirements identified. These alternatives would impose additional mileage and restricted-altitude flight times within TRACON airspace to each flight re-routed. Flights routed via Alternative #4 would encounter significant mileage increases. This study determined that any of these alternatives would produce a very significant increase in the number and duration of departure delays at Seattle-Tacoma International Airport.

The workgroup also conducted an examination of a Port of Seattle request to consider increasing the hours of the "curfew" on north-flow right-turn operations. Analysis of extending curfew hours as an option indicates that this would be feasible only with a significant increase in delays to maintain safety during increased traffic periods. The workgroup determined that it is highly probable that increasing traffic volumes during the first curfew hour (10:00 p.m. to 11:00 p.m.) will soon require that the curfew be shortened on week nights to accommodate those increases. The workgroup also determined that it could be feasible to increase the Saturday evening to Sunday morning curfew hours from 9:00 p.m. to 8:00 a.m. when traffic conditions permit. The workgroup determined that the TRACON should explore expanding and contracting the curfew accordingly.