Impact of Select Uncertainty Factors and Implications for Experimental Design
September 2012
Gareth O. Coville, The MITRE Corporation
Billy Baden, Jr., The MITRE Corporation
Rishi Khanna, The MITRE Corporation
ABSTRACT
Performance estimates produced by a National Airspace System (NAS)-wide simulation
models vary due to the complexity and amount of variability that occurs within the NAS.
One area of modeling variability which current NAS-wide simulation models attempt to
compensate for is the variation in delay occurring across days. This is typically accomplished
through the use of a carefully-selected set of days seeking to be "representative" of the NAS
performance across a given year. These days are referred to as design days. Current
practices model each design day once, with averaging across all design days to yield annual
estimates of performance. The concern with this process is that each design day represents
one specific instance of what could have happened in the NAS and does not consider the
many small daily variations that could have a potentially significant impact. Also, creating
design days is an interactive and time-consuming process, so simply creating additional
design days to improve the confidence of the model results is not always economically
feasible. This paper determines the impact that intra-day perturbations due to four factors
within a NAS-wide model (air carrier delay, runway configuration changes, sector workload
limits and program rate forecasts associated with ground delay programs) have on NASwide
simulation results. This paper also determines the combinations of design days and
iterations per design day required to achieve convergence of NAS-wide estimates for a given
confidence level when the four factors within the model are perturbed. The conclusions of
this paper are that averaging across design days provides a high level of confidence in the
results up to a point but for even higher levels of confidence it becomes important to include
iterations in the experimental design. The four factors added an additional 37% NAS-wide
delay to the model results. We expected the four factors to increase delay in model results as
some of these factors were not previously modeled and are new forms of delay. The factor
that contributed the most to the variability of NAS-wide delay was the program rate
forecasts associated with ground delay programs.
Additional Search Keywords
National Airspace System, NAS, NAS uncertainty factors, air carrier delays, runway configuration changes, NAS-wide performance, Next Generation Air Transportation System, NextGen
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