Prediction Uncertainty Reduction Tech Challenge: Final Report

In 2018, several companies were requesting that the Federal Aviation Administration (FAA) establish
a regulation for certifying commercial supersonic aircraft, including their noise during landing and takeoff
(LTO). Regulators, having no technical data to judge reasonable noise levels for such aircraft, were
turning to NASA and other experts to use their noise prediction models to guide the formulation of such
regulations. Ultimately, a Notice of Proposed Rulemaking was released by the FAA, largely based on
studies using the best prediction methods available. However, during these studies it became clear that the
uncertainty in aircraft noise predictions, when applied to supersonic vehicles, was much greater than what
regulators were accustomed to, leaving the regulators on shaky ground in making new noise rules.

As a result of a January 2021 Tollgate review, the Advanced Air Vehicles Program approved a new
Technical Challenge (TC) to be run out of the Commercial Supersonic Technology (CST) Project. The
TC was called “Prediction Uncertainty Reduction (PUR).” The final TC statement was “Produce data
and demonstrate tools that reduce the uncertainty in predicting Landing & Takeoff Noise levels of
supersonic-relevant designs by 5 EPNdB and are ready for use in studies to inform FAA rule-making.”

During the 90-day initial baseline Uncertainty Quantification study that followed, a key performance
metric and Progress Indicator was created and approved by the Program. The key performance metric was
the cumulative error in predicting the certification noise levels of propulsion components appropriate for
supersonic flight as they impacted the total aircraft noise. It was shown that when this metric was applied
to conventional aircraft, such as the 737-800, the cumulative error was 1.5 EPNdB; when applied to the
study vehicle being used in International Civil Aviation Organization studies of supersonic noise
regulations, the cumulative error was 7.8 EPNdB. The TC goal of 5 EPNdB reduction would bring the
uncertainty of predicting supersonic aircraft noise to nearly as low as that of predicting conventional
aircraft.