A key component to achieving NextGen capabilities is the assimilation of weather information into decision-making. Assimilating weather information and its uncertainties into operational decisions is crucial to quantifying user risks (e.g., safety, comfort and convenience of flight, user business objectives, and Air Traffic Management (ATM) initiatives), which are based on operational thresholds and performance goals. Efficiencies can be realized if all National Airspace System (NAS) stakeholders use the same source of weather information. NextGen will provide a reliable, common weather source to a wide range of users. This supports collaborative decision-making by enabling air transportation decision-makers to be in-sync on the timing of Federal Aviation Administration (FAA) ATM, airline, or pilot actions.
The FAA convened a multi-disciplinary NextGen Weather Performance Requirements Team (NWPRT) to develop the weather performance requirements for NextGen Full Operational Capability (FOC) . The NWPRT used the functional requirements from the JPDO-sponsored weather functional analysis, published in January 2008, as the baseline requirements for their task. The team used concepts in the NextGen Concept of Operations to develop assumptions and rationales for weather performance values.
2.0 PURPOSE The intent of this paper is to aid the ATM and operational user communities in validating NWPRT assumptions and rationales. Their feedback will provide a better understanding of ATM user needs and result in the modification of incorrect assumptions and the associated performance values. This work also illustrates the need for further validation of weather performance requirements by performing operational research coupled with modeling and simulation.
3.0 METHODOLOGY AND ASSUMPTIONS The NWPRT reviewed various NextGen far- and mid-term documents to understand desired operational performance improvements. These references for the envisioned NextGen ATM functionality support the following operational arenas:
- Surface Movement Management - Staffed/Automated NextGen Towers - Integrated Arrival/Departure Management - En Route Operations - Traffic Flow Management
3.1 Weather Information Consistency
A number of these operational arenas need the same type of weather information at the same time. For example, wet or icy airport surfaces affect braking distances (e.g., runway and taxiway) and surface movement initiatives. As a result, airport arrival rates are reduced, which influences En Route and Traffic Flow Management decisions.
3.2 Solution-Independent Approach
The emphasis of the NWPRT was to develop solution-independent performance requirements. For example, the team did not define performance in terms of dBZ because that is solution specific (i.e., radar). Rather, the team developed requirements in terms of meteorological elements that impact operations. For example, the amount of water suspended in the air has operational ties to engine flameouts. Thus, the team developed performance requirements for liquid water content.
3.3 Weather Performance Drivers
NextGen operational decision-makers need to be confident that they can rely on the weather information they receive. Therefore, the values for observed and forecast weather elements must be sufficiently accurate for NextGen decision-making and for assimilation into their decision support tools. Decision-makers also need the weather information to be delivered with user-specified temporal and spatial resolution, forecast accuracy, and latency. For the concept of virtual aircraft departure queues, the availability of accurate weather supports effective departure scheduling, where the aircraft is at the gate with engines off versus on the taxiways. For example, observed temperatures with an accuracy of plus or minus 0.5 degree and forecast temperatures with an accuracy of plus or minus 1.0 degree facilitate departure queue timing calculations for de-icing/anti-icing activities.
The NWPRT identified performance values for all the weather elements that are required for operational decision-making. In general, these values have the highest performance in high-density terminal airspace. For example, the update interval for observations of convective weather elements is less than or equal to 1 minute in high-density terminal airspace. This performance requirement is consistent with the need to know the weather conditions for landing and take-off and is based on the assumption that aircraft operating in high-density airspace will arrive and depart approximately every minute.
Weather information must be at a sufficient density (e.g., at locations or points in space) to represent the weather in between known locations to the required accuracy. Operational needs drive these requirements. It is also important to inform operational decision-makers if and how fast the weather is changing. This is especially true when the weather conditions approach or pass through an operational threshold. This alerts users of the potential need to adjust an operation. Faster weather updates are required where the greatest sensitivity to changing weather exists. The need for an operation to reassess the potential weather impact drives the weather forecast update frequency. For example, the weather performance is the most stringent for current and forecast weather conditions in high-density terminal airspace where there is the greatest
- Number of operations - Complexity of operations - Precision of operations
NextGen operations conducted in en route or global airspace require less constrained performance values. However, those weather elements that impact safety will have the same required measurement performance regardless of airspace. For example, convection and turbulence can have a very high operational impact regardless of the airspace.
The FAA NWPRT developed the weather performance requirements for NextGen FOC and NextGen Mid-Term Operational Capability (MOC). The performance values were developed based on operational needs specified in a number of concepts of operations. All requirements will be fully validated before allocation to a specific solution.
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