Density Altitude Variations and Runway Lengths

The necessity of accurate knowledge of changing meteorological conditions, particularly air temperature and pressure altitude, at departure airports was recognized prior to the introduction of Jumbo-jet aircraft into service. Previous studies on the effect of variations in these two variables were made and, because the effects of pressure altitude variations were smaller than the effects of temperature variations, pressure accoutability was not made a part of the U.S. regulations. A different form of presentation of computed runway lengths, with and without pressure accountability utilizing a probability plot, results in a much broader picture of the effects and permits an analysis both from the point of view of the aircraft operator and the airport designer. The results of the study indicate that payloads can be effected from 1.5% to 13%, or the required runway length can vary from 1% to 4%, or both.