ATM-Weather Integration Plan - Joint Planning and Development ...

Joint Planning and Development Office (JPDO)
DRAFT v0.7
ATM-Weather Integration Plan
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weather counts. Regions where weather-impacted counts are low relative to fair-weather counts
are assumed to be areas that pilots are avoiding due to the weather present in the area. The
correlation of observed weather with areas of avoidance is used to identify the weather
characteristics that best predict the observed weather avoidance.
Both approaches have strengths and weaknesses. Trajectory classification is highly labor
intensive, restricting the size of the statistical dataset used in the model, but gives very detailed
insights into pilot behavior. Spatial cross-correlation greatly reduces the labor involved in the
analysis, vastly increasing the modeling dataset, but does not provide information about
individual decisions. Spatial cross-correlation is also subject to errors arising from the displaced
weather impacts (e.g., local air traffic counts are abnormally low because airways leading to the
region are blocked by weather upstream) or traffic management initiatives that distort demand
(e.g., pro-active reroutes to avoid predicted weather that does not materialize as expected).
To date, CWAM studies have only considered weather characteristics derived from groundbased
weather radar products (precipitation intensity, echo top height). Studies using both
methodologies have identified the difference between aircraft altitude and echo top height as the
primary predictor of weather-avoiding deviation in en route airspace, with precipitation intensity
playing a secondary role. Current CWAM are most prone to error for en route traffic flying at
altitudes near the echo top, particularly in regions of moderate precipitation intensity. Since
current CWAM are based only on ground-based weather radar, they do not readily discriminate
between relatively benign decaying convection and stratiform rain and turbulent downwind from
thunderstorms, both of which are often characterized by echo tops in the 30-40 kft. range and
moderate precipitation intensities [DCF09]. Further research is needed to examine additional
weather information (e.g., satellite, winds, convectively-induced turbulence estimates [CML04])
that may help differentiate between benign and hazardous regions with similar radar signatures.
Research is also needed to identify the human factors associated with pilot decision-making,
particularly in circumstances where CWAM performs poorly.
B-1.2 Terminal Convective Weather Avoidance Modeling
In order to determine the impacts of convective weather on terminal air traffic operations, it is
necessary to partition terminal area airspace into passable and impassable regions. CWAM that
take into account the constraints of terminal area flight need to calculate WAFs that apply
specifically to terminal area operations. Each WAF grid point is assigned a probability and/or a
binary value (0 or 1) that represents that likelihood that pilots will choose to avoid convective
weather at a point location in the terminal area.
CWAM for terminal areas are likely to differ from en route CWAM in significant ways.
Departures and arrivals are constrained to follow ascending or descending trajectories between
the surface and cruise altitude, leaving little flexibility to avoid weather by flying over it. Pilots
of aircraft ascending or descending through weather are likely to have few or no visual cues to
inform their decision, unlike those in en route airspace who may have clear views of distant
thunderstorms as they fly above the clouds. Aircraft flying at low altitudes in the terminal area
appear to penetrate weather that en route traffic generally avoids [K08]. The willingness of pilots
to penetrate severe weather on arrival increases as they approach the ground [RP98].
B-2 April 22, 2009