Density altitude: Climatology of Daily Maximum Values and Evaluation of Approximations for General Aviation

Abstract

Density altitude (DA) is an aviation parameter that helps determine specific aircraft performance characteristics for the expected atmospheric conditions. However, there are currently no detailed graphical tools for general aviation (GA) pilot education demonstrating the spatial and temporal variation of DA to help improve situational awareness. In this study, the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis of the global climate (ERA5) dataset is used to construct a 30-year monthly climatology of DA for the conterminous United States. Several DA characteristics are also investigated, including the effect of water vapor on DA, the determination of reasonable worst-case conditions, and the applicability of two DA rules-of-thumb (ROTs). Maximum values of DA (worst aircraft performance) occur during July reaching 3,600 m over areas with high surface elevations. Humidity, while tertiary to the effects of temperature and pressure, cause the DA to increase from their dry values by more than 140 m as far north as the U.S./Canada border. The dry DA ROT performs well for all conditions outside of strong tropical cyclones, where GA flights would not be expected. The ROT to correct for the effects of water vapor performs well except in high elevations or when the dew point temperatures fall outside the applicable range of ≥5°C. When applied outside this range, in some situations, DA errors can be greater than if no humidity correction were applied. Therefore, a new humidity ROT is introduced here which extends the applicable dew point temperature range to ≥-28°C and reduces DA errors.