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The crew oxygen masks are only required to function (oxygen flow and test) at -5 °C and warmer. If the cabin has been allowed to cold soak below this temperature, it may be necessary to warm the cabin prior to testing the masks during the preflight inspection. NORMAL When the control knob is in the normal (N) position, the oxygen supplied to the mask is a mixture of ambient air and pres-surized oxygen. In this position, the operator can turn the flow control knob to adjust the flow. 100% When the control knob is in the 100% position, the mask is provided with pure oxygen. EMERGENCY The emergency flow control knob is also located on the regulator unit. If the knob is turned clockwise to the EMERGENCY position, the mask supplies a constant flow of oxygen at a permanent positive pressure. At high cabin altitude (above 35 000 ft) the mask supplies only pure oxygen at a constant flow, regardless of the knob position. PRESS TO TEST When the press to test button is pushed, oxygen is momentarily supplied to the mask and the hose flow indicator will change color. INFLATABLE HARNESS CONTROL The oxygen mask is extracted from the stowage box by gripping the plates of the regulator, which protrude out of the box. When the two red tabs on the mask are squeezed, the harness inflation valve will open permitting the harness to inflate. When the tabs are released, the harness deflates and the mask holds tightly against the operator’s face. CONTROL KNOB REGULATOR CREW OXYGEN MASK MICROPHONE CONTROL OXYGEN LINE DESCRIPTION COMPONENTS AND OPERATION The electrical pneumatic actuating valve (EPAV) controls oxygen availability to the passenger oxygen distribution system and provides for automatic or manual mode selection. The control is a three-position PAX switch on the OXYGEN panel labeled OFF, PAX AUTO, and DEPLOY. |