Crew masks are designed to fit completely and reasonably tightly over a pilot’s nose and mouth. The mask may also come with attached smoke goggles – in this case, the mask will be a single unit with clear portion that goes over the eyes and a oxygen mask portion that go over the nose and mouth. A picture of a crew mask is shown in Figure 1. Another picture of a crew mask that contains smoke goggles is shown in Figure 2.
Figure 1 Demand / Diluter Demand Oxygen Mask without Smoke Goggles
Figure 2 Demand / Diluter Demand Oxygen Mask with Smoke Goggles
Crew masks will be capable of flowing 100% oxygen (full demand) or partial oxygen (diluter demand). Full demand mode is used when an aircraft has depressurized and cabin altitude is above approximately 30,000 feet. In diluter demand mode, the mask has an opening that allows cabin air to supplement oxygen flow, thus reducing the oxygen flow (in full demand mode this opening is shut so that cabin air is not allowed to flow into the mask). Diluter demand is used when a pilot is using oxygen above certain aircraft altitudes. For example, for flight crew operating under FAA Part 135 rules (135.89), one flight crewmember is required to have mask on flowing diluter demand at altitudes above 35,000 feet or any time the other crewmember has temporarily left the cockpit. Crew masks will also contain a flow indicator, which indicates to the user that oxygen is flowing to the mask. Microphones may also be part of the crew mask assembly. The microphone should not interfere with operation or donning of the crew mask. Crew masks should be capable of being donned within 5 seconds using one hand. The crew masks will normally reside in a “box” that is made by the same manufacturer as the mask manufacturer. The box can be located on the seat or the side panel next to the seat. The key aspects for selecting mask location is that the mask must be within easy reach and must be able to be donned properly with one hand in 5 seconds. The crew masks will have straps (similar to a baseball catcher’s mask) to hold the mask on the crewmember’s face. The straps have some adjustability and flexibility.
As described above, crew masks will have oxygen inlet that connects to the oxygen supply, diluter valve, outflow valve (to exhaust air from the mask when breathing out), flow indicator, optional smoke goggles and optional microphone. Under FAA regulations, crew masks are designed to meet the standards of Technical Standard Order (TSO) C78. TSO C78 specifies flow requirements at different altitudes as well as qualification and performance test requirements. Another source of design requirements for demand masks is SAE AS 8026, Crewmember Demand Oxygen Mask for Transport Category Aircraft. As a general rule, when selecting a crewmember demand oxygen mask, the mask should contain the desired features and meet the requirements of TSO C78 and/or AS 8026.