Aircrafts’ Altitude Measurement Using Pressure Information: Barometric Altitude and Density Altitude TEODOR LUCIAN GRIGORIE Avionics Department University of Craiova 107 Decebal Street, 200440 Craiova ROMANIA lgrigore@elth.ucv.ro http://www.elth.ucv.ro LIVIU DINCA Avionics Department University of Craiova 107 Decebal Street, 200440 Craiova ROMANIA ldinca@elth.ucv.ro http://www.elth.ucv.ro JENICA-ILEANA CORCAU Avionics Department University of Craiova 107 Decebal Street, 200440 Craiova ROMANIA jcorcau@elth.ucv.ro http://www.elth.ucv.ro OTILIA GRIGORIE Carol I, High School 2 Ioan Maiorescu Street, 200418 Craiova ROMANIA ogrigorie@yahoo.com Abstract: - The paper is a review of the pressure method used in the aircrafts’ altitude measurement. In a short introduction the basic methods used in aviation for altitude determination are nominated, and the importance of the barometric altitude is pointed. Further, the atmosphere stratification is presented and the general differential equation, which gives the dependence of the static pressure by the altitude, is deduced. The barometric and the hypsometric formulas for the first four atmospheric layers are developed both in the analytical and numerical forms. Also, the paper presents a method to determinate the density altitude with an electronic flight instrument system. A brief review of the flight altitudes is performed, and the calculus relations of the density altitude are developed. The first two atmospheric layers (0÷11 Km and 11÷20 Km) are considered. For different indicated barometric altitudes an evaluation of the density altitude, as a function of non-standards temperature variations and of dew point value, is realized. Key-Words: - standard atmosphere; atmospheric layers; barometric formula; density-altitude; evaluation 1 Introduction Seen like one of the most important parameters for the flight safety, the altitude can be defined as the distance between the aircraft centre of mass and the point when the local vertical intersects the surface of Earth [1]. The measurement of the altitude can be made directly, with the altimeters, or indirectly, situation in which it is calculated by means of complementary systems, such as, for example, Air Data Computer (ADC), Inertial Navigation System (INS) or Global Positioning System (GPS) [2]÷[5]. Showing altitude information on board WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Teodor Lucian Grigorie, Liviu Dinca, Jenica-Ileana Corcau, Otilia Grigorie ISSN: 1109-2734 503 Issue 7, Volume 9, July 2010