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Dynamic Weather Routes

What's the Problem? Severe thunderstorms are the leading cause of delay in US airspace. When such weather is present or forecast on preferred flight routes, weather avoidance routes are selected, usually 1-2 hours before takeoff, and often include large buffers to forecasted weather. As flights progress, airline dispatchers and Federal Aviation Administration (FAA) traffic managers strive to find improved routes to reduce delay. However, operators are especially busy during weather events, and workable opportunities for more efficient routes around bad weather are missed. Automation does not exist to indicate when weather avoidance routes have become stale and could be updated to reduce delay.

This animation shows a typical day of air traffic in the national airspace system during convective weather and the scope of the air traffic delay problem. The dots represent actual flights. The gray flights are on time. The flights with blue streaks are delayed between 15 minutes to 2 hours. The flights with red streaks are delayed 2 hours or more.

What's NASA Doing to Help? NASA has developed a ground-based automation system called Dynamic Weather Routes (DWR). DWR continuously and automatically analyzes in-flight aircraft in en route airspace to find opportunities for time- and fuel-saving corrections to weather avoidance routes. Route corrections are simple reroutes like those typically used in today's operations.

This image shows the DWR concept. The left side shows a cluster of weather cells and a line passing around, but close to the weather, that represents a weather avoidance route that is implemented one hour before takeoff. The right side shows that the same cluster of weather cells has evolved and moved. Now the original weather avoidance route is stale and inefficient because there is a rather large buffer between it and the weather. Another line that is dashed represents the new dynamic weather route that is proposed while the flight is en route. The DWR passes closes to the weather and is a more efficient route that saves 5 or more minutes of flying time relative to the original flight plan.

Every 12 seconds, DWR computes and analyzes trajectories for en route flights. DWR first identifies flights that could save 5 or more flying minutes (wind-corrected) by flying direct to a downstream “return” fix on their current flight plan. Eligible return fixes are limited so as not to take flights too far off their current route or interfere with arrival routings near the destination airport. Usually such direct routes that can save 5 or more minutes are due to route segments included to avoid weather. Using the direct route as a “reference route,” DWR inserts up to two auxiliary waypoints as needed to find a minimum-delay route correction that avoids the weather, or optionally weather and traffic conflicts, and returns the flight to its planned route at the downstream fix. If a route correction is found that can save 5 minutes or more relative to the current flight plan, the flight is posted to a list displayed to an airline or FAA user. Auxiliary waypoints are defined using fix-radial-distance format, but a “snap-to” option utilizes nearby named fixes for ease of use in today's operations. Users may adjust the alert criteria, nominally set to 5 minutes, based on their workload and desired potential savings for their flights.

This image shows the DWR automation concept. In the center of the graphic there is a cluster of weather cells. There is a solid line starting from the aircraft icon that passes around the weather to the return capture fix (inside the limit region, or the last fix before STAR) with a rather large berth and represents the current active Center flight plan route. A dotted line goes directly from the aircraft to the return capture fix and passes through the weather and represents the direct reference route. The reference route provides 5 minutes or more of wind corrected time savings. A dashed line representing the dynamic weather route passes around the weather with a smaller spacing buffer than the current active flight plan. The dashed line passes through a triangle that represents the waypoint that is inserted for minimum delay weather or weather and traffic resolution. Near the triangle, and off the dashed line, is a circle that represents the snap-to nearby named fix option.
DWR Automation Concept

In addition to the primary en route Center traffic data input to DWR, national traffic data are used to probe DWR-advised routes for downstream sector congestion on both the existing flight plan and the DWR routes. DWRs are also tested for conflicts with special use airspace and for FAA route restrictions.

Screenshot of the DWR user interface.
Graphical user interface showing a trial Dynamic Weather Route (DWR). (Click image for larger version.)

A graphical user interface enables users to visualize proposed routes on a traffic display and modify them if necessary using point, click, and drag inputs. If needed, users can adjust the return fix, auxiliary waypoints, and the maneuver start point. Metrics, including flying time savings (or delay), proximity to current and forecast weather, downstream sector congestion, traffic conflicts, and special use airspace conflicts all update dynamically as the user modifies a proposed route.

This animation shows a few hours of air traffic in the national airspace system during heavy convective weather. The flights with blue streaks are those for which a DWR route advisory with potential time savings of 5 min. or more has been computed. When determining reroutes, DWR considers storm intensity and height along with growth, decay and movement over time. A few of the DWR-advised flights seen here appear to be traveling through the severe weather, but are actually flying over it.

Potential Benefits. An analysis of all Fort Worth Center traffic in 2013, excluding arrivals to the major Dallas airports, Dallas-Fort Worth International (DFW) and Dallas Love Field (DAL), indicates a potential savings of about 100,000 flying minutes for 15,000 flights, or about 6.7 minutes/flight on average. These potential savings are over and above the savings flights achieve today through normal pilot requests and controller clearances without DWR. On heavy weather days the potential savings for some DWR routes can range from 20 minutes to over 40 minutes for an individual flight.

Evaluation at American Airlines. Since July 2012, DWR has been in operation at the American Airlines (AA) Integrated Operations Control Center in Fort Worth, Texas, where NASA and AA are conducting an operational evaluation of DWR. Testing is currently limited to AA flights in Fort Worth Center airspace, and since May 2014, AA flights in Fort Worth Center plus its first-tier adjacent Centers (Kansas City, Memphis, Houston, and Albuquerque). A DWR display runs at the Air Traffic Control (ATC) Coordinator Desk where an audible alert sounds when a new AA flight is first posted to the DWR Flight List. An AA ATC coordinator evaluates the proposed route and consults with the dispatcher responsible for the flight. If both agree, the ATC coordinator clicks an “Accept” button on the DWR user display, and the dispatcher sends the proposed route correction to the flight crew (via the Aircraft Communications Addressing and Reporting System, or ACARS). The flight crew evaluates the route change and, if they concur, requests the route change from air traffic control, using today's normal procedures.

Photo of an American Airlines System Operations Center ATC coordinator using a workstation running DWR
DWR user display at American Airlines Integrated Operations Control Center, Fort Worth, Texas.

Results. Test results for the period Jan 2013 through Sept 2014 show that 65% of routes advised by DWR and evaluated by AA users were rated acceptable. Potential savings for the DWRs rated “Accept” totaled 8,866 flying minutes for 1,311 flights, and feedback from AA users indicates that ACARS messages with proposed route changes were sent to about 90% of these flights. An analysis of actual Center route amendments indicates an estimated actual savings of 3,290 minutes for 526 AA flights, or 37% of attempted savings.

These savings achieved during voluntary testing by AA are significant, but actual savings are projected to be quite a bit higher. For example, due to staffing limits during the testing phase, only 22% of DWR advisories were evaluated by AA users. Some of the DWR advisories were rejected due to close proximity to weather or merging arrival streams, as well as workload required due to inter-Center coordination. DWR is being further developed to address these problems in order to increase its usage and potential savings. Air/ground data communication (Data Comm) and other automation to streamline route change coordination could also significantly improve actual DWR savings.

Sample Fort Worth Center reroutes from 2012 Operational Trial with American Airlines

It is known that some flights get some percentage of potential DWR savings today, without DWR, through normal pilot requests and controller clearances. An analysis of 1,118 AA and non-AA flights over 29 heavy weather days was conducted to estimate how much more savings AA flights get when DWR is used vs. when DWR is not used. Results show that AA flights where DWR was used realize 20% more savings relative to AA and non-AA flights where DWR was not used. Total advised savings for AA flights over the 29 days was 5,417 minutes for 526 flights. Assuming a 20% net savings and an operating cost of $100/minute, this equates to about $100,000 net savings in operating costs for one airline in one Center over 29 days.

A sector congestion analysis compared the total time sectors in five Centers (Fort Worth Center plus its first-tier adjacent Centers) spent in Monitor Alert congestion status under two traffic scenarios. Under the baseline scenario, all flights fly their nominal weather avoidance routes. Under the DWR scenario, all flights for which DWR advisories were computed fly their DWR routes. Results, based on analysis of traffic on 30 heavy-weather days with DWR advisories for 7,098 flights, show that the total time all sectors spend in congestion status is reduced by 19% under the DWR scenario relative to the baseline.

Next Steps. AA feedback has been favorable, and other airlines, aerospace companies, and the US Air Force have expressed interest in the DWR concept and software. NASA is supporting technology transfer of DWR for commercialization, and DWR automation is being leveraged to find common route corrections for groups of flights, including arrival streams merging and descending into the terminal area.

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DWR: 1,241 flying minutes saved
Estimated actual Dynamic Weather Routes (DWR) flying time savings for 260 American Airlines revenue flights in Fort Worth Center from July 31, 2012 to November 5, 2013.
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Dynamic Weather Routes: Overview for Technology Transfer
Presented on 4/29/14 by Dave McNally, Kapil Sheth, Hassan Eslami, and Chester Gong. This webinar describes the trajectory automation concept, the prototype system including the required input data feeds, potential benefits to airspace users, and results from operational testing at American Airlines.
+ Stream the video via Adobe Connect
+ Watch the video on YouTube
+ Download the slides

Dynamic Weather Routes: The Search for Smarter Flight Routes
NASA Aeronautics Research Institute Presentation given on September 5, 2013 by Dave McNally. (Adobe Connect)
+ Stream Video
US Patent Office Issues Dynamic Weather Routes patent
November 5, 2015
On October 27, 2015, the United States Patent Office issued Patent 9,171,473, titled, “Method and system for dynamic automated corrections to weather avoidance routes for aircraft in en route airspace.”
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PDRC and DWR featured in NASA's “This Year@NASA” for 2014
December 19, 2014
Two new technologies in development in the Aviation Systems Division were featured in NASA's top stories of the year. Check it out, beginning at the 5:40 mark.
+ View on YouTube

Provisional Patent Filed for NAS-based Airborne Rerouting Technology
November 14, 2014
The NASCENT (NAS Constraint Evaluation and Notification Tool) software implemented NASA's Dynamic Weather Routing (DWR) tool algorithm with a few novel techniques, which extends the DWR reroute advisories to the NAS.
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NASA Tool Helps Airliners Minimize Weather Delays
October 15, 2014
DWR web feature on
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Innovator Spotlight: Dave McNally
October 12, 2014
Dynamic Weather Routes (DWR) and principal investigator Dave McNally are profiled in the NASA Technology Transfer Portfolio.
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Weather software developed by NASA helps save American fuel
September 19, 2014
Article by Star-Telegram about how American Airlines is using the new NASA-developed tool, called Dynamic Weather Routes, to reduce delays and save fuel.
+ Read the article and watch the video

NASA taps Global Hawk pilots for 'Post Gen' research
DWR Software Upgrade for American Airlines Trial System
May 29, 2014
The Dynamic Weather Routes (DWR) software that supports the operational trial of DWR at the American Airlines Integrated Operations Center in Fort Worth, Texas was upgraded on May 9, 2014.
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GE Aviation and GE Global Research Explore Dynamic Weather Routes
May 29, 2014
GE Aviation Systems and GE Global Research have expressed strong interest in the Dynamic Weather Routes (DWR) concept and software, sending seven staff members to NASA Ames Research Center on May 20-21, 2014 to work with NASA's DWR software team.
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American Airlines revenue flights gain 10% more savings when using NASA Dynamic Weather Routes (DWR) tool
December 13, 2013
Results from operational testing of NASA's DWR tool at American Airlines (AA) show that AA revenue flights achieved 10% more savings on days where DWR was heavily used by AA vs. days where DWR was lightly used.
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Dynamic Weather Routes presented at UC Berkeley Seminar
October 21, 2013
Principal investigator David McNally gave an invited presentation of the Dynamic Weather Routes (DWR) concept and American Airlines initial trial results at the University of California at Berkeley Transportation Seminar Series.
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Dynamic Weather Routes (DWR) Release 2.0 Installed at American Airlines Integrated Operations Center
July 11, 2012
The Dynamic Weather Routes (DWR) software Release 2.0 was installed on the American Airlines (AA) trial system in Fort Worth, Texas.
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Dynamic Weather Routes (DWR) system evaluated at NASA Ames Research Center
March 22, 2013
From February 26 through March 7, 2013, six recently retired Fort Worth Center Traffic Management Coordinators (TMCs) and Area Supervisors participated in an evaluation of the DWR system.
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"Dynamic Weather Routes Architecture Overview"
Eslami, H., and Eshow, M., 18 Feb. 2014.
+ Download PDF Version

"Strategic Airspace Constraint Analysis and Environmental Impact of Dynamic Weather Routes"
Sheth, K., Sridhar, B., McNally, D., and Petersen, J., 32nd Digital Avionics Systems Conference (DASC), Syracuse, NY, 6-10 Oct. 2013.
+ Download PDF Version

"Operational Evaluation of Dynamic Weather Routes at American Airlines"
McNally, D., Sheth, K., Gong, C., Borchers, P., Osborne, J., Keany, D., Scott, B., Smith, S., Sahlman, S., Lee, C., and Cheng, J., 10th USA/Europe ATM R&D Seminar (ATM2013), Chicago, Illinois, 10-13 June 2013.
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"Dynamic Weather Routes: A Weather Avoidance System for Near-Term Trajectory-Based Operations"
McNally, D., Sheth, K., Gong, C., Love, J., Lee, C.H., Sahlman, S., and Cheng, J., 28th International Congress of the Aeronautical Sciences (ICAS), 23-28 Sep. 2012.
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"Consideration of Strategic Airspace Constraints for Dynamic Weather Routes"
Sheth, K., McNally, D., Petersen, J., Morando, A., and Shih, F., AIAA-2012-5501, 12th American Institute of Aeronautics and Astronautics (AIAA) Aviation Technology, Integration, and Operations (ATIO) Conference, Indianapolis, IN, 17-19 Sep. 2012.
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NASA Fact Sheet
Download the NASA Fact Sheet on DWR.
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