Diluter demand aircraft oxygen masks withhold the flow of oxygen until the user inhales. Pure oxygen supply is diluted with cabin air each time a breath is drawn. As altitude increases, the regulator allows more oxygen and less cabin air to be delivered. At approximately fl340, the diluter-demand goes to 100% oxygen. The emergency switch will also deliver 100% oxygen—but in a continuous flow— bypassing the demand function.
- Diluter demand aircraft crew masks are required equipment for any pressurized civilian aircraft—with service ceilings above FL250 -to FL400.
- If your unpressurized aircraft has a service ceiling over FL250, you must placard your aircraft against flights above the FL250 and use constant flow crew masks. Your older aircraft was once grandfathered for constant flow but today’s OEMs no longer produce constant flow approved for use above FL250.
Pressure demand aircraft oxygen masks operate similarly to diluter demand masks, except that the oxygen is delivered under higher pressure, which forces the oxygen into the lungs of the pilot.
pressure demand crew masks are required equipment for any pressurized civilian factory aircraft with service ceilings above FL400.
Safran (EROS) and Rockwell (Puritan, ZEP) crew masks are no longer manufactured with Scott or Sky Ox connectors (below left image):
Your options are to 1) buy an adapter (below right) for the connector so the mask can be used in multiple aircraft, or 2) change out your aircraft port (center right) to be compatible with your upgraded EROS or BE AERO crew mask connector (center left).
Many countries are considering the requirement that all diluter and pressure demand masks be smoke venting, i.e. to meet TSOC99. If your crew mask is not smoke venting, please consider this when it is time for replacing or overhauling your existing masks. [see Canada AC700-32 for overview of the change]:
CANADIAN AC700-032—GENERAL SUMMARY
- THE WALKAROUND OXYGEN SYSTEM SHOULD PROVIDE BOTH HYPOXIA & SMOKE PROTECTION FOR AIRCRAFT PERSONNEL ACCESSING THE CARGO AREA OR WALKING AROUND THE CABIN—IN CASE OF EMERGENCY DEPRESSURIZATION OR FIRE – WITH PROVISION FOR THE AIRCRAFT MAXIMUM ALTITUDE—OR AT LEAST TO FL400.
- THE COMPONENTS OF THE WALKAROUND SYSTEM SHOULD ALWAYS BE ASSEMBLED SO THAT OXYGEN FLOW IS IMMEDIATE UPON DONNING OF THE MASK AND TURNING ON OF THE TANK.
- MASK TYPES:
- FULLFACE MASK (ONE PIECE NOSE-MOUTH-EYES)
- MASK FOR NOSE-MOUTH WITH SEPARATE GOGGLES FOR THE EYES
- ANY OTHER EQUIVALENT EQUIPMENT
- ANY OF WHICH MUST MEET TSOs C78A & C89A
- POSITIVE PRESSURE (SMOKE-VENTING) GOGGLES TSO C99A ARE NOT REQUIRED—ALBEIT DESIRABLE AND GENERALLY AVAILABLE
NOTES: SMOKE HOODS DO NOT MEET THESE STANDARDS FOR PERSONNEL DURING HIGH ALTITUDE FLIGHTS—NOR DO THE LOW-PRESSURE ZODIAC & BE AEROSPACE 5500, 5600, 9700 OR 9800 AND INTEGRA-SERIES PORTABLES.