Scope of the Initial Issue This report covers engine tests performed in Altitude Test Facilities (ATFs) with the primary purpose of determining steady state thrust at simulated altitude flight conditions as part of the in-flight thrust determination process. As such it is complementary to AIR1703 and AIR5450@ published by the SAE E-33 Technical Committee. The gross thrust determined using such tests may be used to generate other thrust-related parameters that are frequently applied in the assessment of propulsion system performance. For example: net thrust@ specific thrust@ and exhaust nozzle coefficients. The report provides a general description of ATFs including all the major features. These are: ? Test cell air supply system. This controls the inlet pressure and includes flow straightening@ humidity and temperature conditioning. ? Air inlet duct and slip joint. Note that the report only covers the case where the inlet duct is connected to the engine@ not free jet testing. ? Thrust stand force measurement system ? Test cell ? Cell exhaust system ? Measurement system The report provides detailed technical information on how the facilities are operated@ including: ? Program planning guidelines ? Optimization of the tests ? Setting and control of flight conditions ? Assessment of the data A technical discussion provides the underlying physics for: ? Air mass flow determination ? Determination of the conditions in the inlet duct and slip joint ? Derivation of thrust and related parameters ? Correction of data to nominal flight conditions ? Measurement uncertainty The initial issue of this report primarily address ATF testing of engines intended for use on subsonic@ transport aircraft. Future revisions to the report will include greater content relevant to the testing of engines for supersonic aircraft@ including the wider and higher flight envelopes associated with such aircraft and the technical issues raised by these flight conditions.