Downloaded from https://www.everyspec.com MIL-STD-81OC 10 March 1975 METHOD 500.1 LOW PRESSURE (ALTITUDE) 1. PURPOSE. The altitude test is conducted to determine the effects of reduced pressure on equipment. This method is applicable for the purpose of determining the ability of equipment to withstand reduced pressure encoun- tered during shipment by air and for satisfactory operation under those pres- sure conditions found at high ground elevations. 1.1 General effects. Degrading effects may include leakage Of gases or fluids from gasket-sealed enclosures and rupture of pressurized containers.
Under low pressure conditions, low density materials may change their physical and chemi- cal properties. Erratic operation or malfunction of equipment may result from arcing or corona. Greatly decreased efficiency of convection and conduction may occur as heat transfer mechanisms under low pressure conditions are encountered. 2. APPARATUS. Altitude chamber. 3. PROCEDURES ) 3.1 Procedure I Step 1 - Prepare the test item in accordance with General Requirements, 3.2 and maintain standard ambient temperature during the entire test. Step 2 - Decrease the chamber pressure to 429.1 mm of Hg (16.9 inches of Hg or 15,000 feet above sea level) at a rate not to exceed 2,000 fpm.
Maintain this pressure for not less than 1 hour and then operate the test item where applicable and obtain results in accordance with General Requirements, 3.2. (If a sudden loss of pressure in the cargo compartment could cause failure of the test item which could damage the aircraft, the equipment shal1 also be tested to withstand an altitude of 40,000 feet, non-operating.) Step 3 - With the test item not operating, return the chamber to standard ambient conditions at a rate not to exceed 2,000 fpm. Step 4 - @crate and inspect the test item and obtain results in accordance with General Requirements, 3.2. 500.1-1 METHOD 500.1 D 10 March 1975 .,