Metrics for Evaluating the Impact of Weather on Jet Routes

The Route Availability (RA) model assesses the convective weather impacts on routes in the National Airspace System (NAS). RA methods invoke a Convective Weather Avoidance Model (CWAM), Weather Avoidance Field (WAF) generation, MaxFlow/Mincut and/or Route Blockage (RB) techniques in order to assess the impact that convective weather has on a jet route. The RA analysis is spatially confined to lateral regions (left and right of the centerline) around a jet route. The RA model applies to terminal/transition arrival and departure routes as well as en route jet routes. In this paper, we revisit RA modeling in order to capture attributes about how weather impacts routing structures in the NAS. We consider jet routes as well as Standard Arrival Routes (STARs) which include multiple jet routes that form a merge tree routing structure. First, we study the nominal clear weather deviations relative to the jet route or STAR to determine nominal route conformance statistics. We expect that aircraft fly within +/- 4 nmi to the left or right of the route centerline, and compare the observed statistics on clear weather time periods to time periods of light, moderate, and severe weather constraints. As pilots request permission to deviate around weather hazards, the route conformance variance increases, limited by the size, geometry, and location of hazardous weather constraints, sector boundaries, potential conflicts with other aircraft in the sector, or proximity to nearby routes (with or without traffic present). We track how far pilots deviate from a nominal routing structure during weather avoidance maneuvering, and study these weather avoidance trajectories to generate route deviation statistics.

In order to study the relationship between pilot deviations and weather constraints nearby a routing structure, we define two wiggle room metrics, a local wiggle room and global wiggle room metric, based on the weather constraints in a sector of airspace and where the weather constraints reside relative to a routing structure and sector boundaries.

The concept of a local wiggle room metric is designed to address the situation in which the pilot deviates away from the routing structure but remains locally nearby the routing structure. The local wiggle room metric measures how much “room” there is between the routing structure and nearby constraints, to identify how much room exists for the pilot and controller to utilize in avoiding weather hazards that reside nearby the nominal routing structure.

The concept of a global wiggle room metric is designed to address the situation in which the pilot deviates significantly from the routing structure, potentially flying around hazardous weather constraints, loosing line of sight with the routing structure, returning back to the routing structure presumably after successfully avoiding the weather constraint.

In this effort, we study pilot deviations in response to weather, in order to see if they can be classified as weather avoidance maneuvers within the local wiggle room, or if they reside in global wiggle room, or if a constraint is violated (weather hazard, nearby route, or sector boundary constraint).

Given the wiggle room statistical analysis, we next look at the relationship between the amount of wiggle room that is available and the deviation statistics that are determined by the observed pilot behavior. We investigate the upper bounds on wiggle room in order to determine the operational limits to weather avoidance maneuvering for jet route and STAR routing structures. When the wiggle room approaches zero, we postulate that the routing structure will be unusable (in other words, route blockage occurs). Thus, we arrive at RA and RB conditions based on the wiggle room metrics for a given routing structure.

Real weather data and current routing structures are used in this analysis.