"Hot Day", "Tropical Day", "Standard Day", "Polar Day" and "Cold Day" are part of the lexicon of the aircraft industry. These terms are generally understood to refer to specific, generally accepted characteristics of atmospheric temperature versus pressure altitude. There are also other, less well-known days, defined by their frequency of occurrence, such as "1% Hot Day", "10% Cold Day", or "Highest Recorded Day". These temperature characteristics have their origins in multiple sources, including U.S. military specifications which are no longer in force.

Purpose

This document is intended to preserve the commonly used day types in an accessible form for future use, make recommendations for their consistent usage, and collect the data in a single format.

Field of Application

These day types find their most frequent application in aircraft and propulsion system computer simulations. They do not impose any requirements on system design, but rather form a common frame of reference for defining the conditions under which various types of analyses are to be performed. Day types provide both a convenient mechanism for setting up computer program input and a convenient shorthand for discussing operational environment. For example, an airframe company might request engine data on a Hot Day to determine hot-day aircraft payload or range capability.

Except for Standard Day, the source data for this document covers a pressure altitude range from sea level to either 100000 ft (30.48 km) or 30 km (98425 ft), depending on the source. All tables in Section 5 have been extended to -2000 ft. (The ambient pressure at -2000 ft is higher than the highest barometer reading ever recorded at sea level.) The tables in Appendix A have not been extended.