Supplemental Oxygen and Pressurization

PRESSURIZED CABIN AIRCRAFT (§ 91.211)

Above FL 250: At least 10 minutes supply of supplemental oxygen must be available for each occupant in the event a descent is necessitated by a loss of cabin pressurization.

Above FL 350: At least one pilot at the controls must be wearing an oxygen mask at all times unless equipped with quick-donning masks. When only one pilot is seated at the controls, pilot must wear the mask at all times even with quick-donning masks.

Above FL 410: One pilot must wear the mask at all times even with quick donning masks.

PRESSURIZED AIRCRAFT – BASIC COMPONENTS (8083-25 / AC 65-15A)

A person who applies for commercial pilot certificate with an airplane category rating and does NOT hold an INSTRUMENT RATING in the same category and class: “The carriage of passengers for hire in on x-country flights in excess of 50 NM or at night is prohibited:

PRESSURIZED AIRCRAFT (8083-25: 6-32 ~ 34)

In a typical pressurized system, the cabin, flight compartment, and baggage compartments are incorporated into a sealed unit capable of containing air under a pressure higher than outside atmosphere pressure.

Air is released from the fuselage by an outflow valve. By regulating the air exit, the outflow valve allows for a constant inflow of air to the pressurized area.

A cabin pressurization system typically maintains a cabin pressure altitude of approximately 8,000 ft at the maximum designed cruising altitude of an aircraft.

Pressurization of the aircraft cabin is an accepted method of protecting occupants against the effects of hypoxia.

* Terms

l  Aircraft altitude: the actual height above sea level at which the aircraft is flying

l  Ambient temperature: the temperature in the area immediately surrounding the aircraft

l  Ambient pressure: the pressure in the area immediately surrounding the aircraft

l  Cabin pressure: cabin pressure in terms of equivalent altitude above sea level

l  Differential pressure: the difference in pressure between the pressure acting on one side of a wall and the pressure acting on the other side of the wall. In aircraft air-conditioning and pressurizing systems, it is the difference between cabin pressure and atmospheric pressure.

The cabin pressure control system provides cabin pressure regulation, pressure relief, vacuum relief, and the means for selecting the desired cabin altitude in the isobaric and differential range.

The cabin pressure regulator controls cabin pressure to a selected value in the isobaric range (altitude) and limits cabin pressure to a preset differential value in the differential range (cabin pressure vs. atmospheric pressure).

The cabin air pressure safety valve: A combination pressure relief, vacuum relief, and dump valve

l  Pressure relief valve: prevents cabin pressure from exceeding a predetermined differential pressure above ambient pressure.

l  Vacuum relief valve: prevents ambient pressure from exceeding cabin pressure by allowing external air to enter the cabin when the ambient pressure exceeds cabin pressure.

l  Dump valve: actuated by a cockpit control that will cause the cabin air to be dumped overboard.

Decompression is defined as the inability of the aircraft’s pressurization system to maintain its designed pressure differential. The primary danger of decompression is hypoxia

OXYGEN SYSTEMS (8083-25: 6-34 ~ 35)

Aircraft oxygen is usually stored in high pressure system containers of 1,800 ~ 2,200 psi.

When the ambient temperature surrounding an oxygen cylinder decreases, pressure within that cylinder decreases because pressure varies directly with temperature if the volume of a gas remains constant.

The containers should be supplied with aviation oxygen only, which is 100% pure oxygen.

An oxygen system consists of a mask or cannula and a regulator that supplies a flow of oxygen dependent upon cabin altitude.

Diluter-Demand Oxygen Systems

DILUTER-DEMAND OXYGEN SYSTEMS (8083-25: 6-36)

Diluter-demand oxygen system supply oxygen only when the user inhales through the mask.

Automix lever allows the regulators to automatically mix cabin air and oxygen or supply 100% oxygen.

The demand mask provides a tight seal over the face to prevent dilution with outside air and can be used safely up to 40,000 ft.

A pilot who has a beard or mustache should be sure it is not interfere with the sealing.

PRESSURE-DEMAND OXYGEN SYSTEMS (8083-25: 6-36)

Pressure-demand oxygen systems are similar to diluter demand oxygen equipment, except that oxygen is supplied to the mask under pressure at cabin pressure altitudes above 34,000 ft.

Pressure-demand regulator create airtight and oxygen-tight seals, but they also provide a positive pressure application of oxygen to the mask face piece that allows the user’s lungs to be pressurized with oxygen.

This feature makes pressure demand regulators safe at altitudes above 40,000 ft.

CONTINUOUS-FLOW OXYGEN SYSTEMS (8083-25: 6-36)

Continuous-flow oxygen systems are usually provided for passengers.

The passenger mask typically has a reservoir bag, which collects oxygen from the continuous-flow oxygen system during the time when the mask user is exhaling.

The oxygen collected in the reservoir bag allows a higher aspiratory flow rate during the inhalation cycle, which reduces the amount of air dilution.

Ambient air is added to the supplied oxygen during inhalation after the reservoir bag oxygen is depleted.

The exhaled air is released to the cabin.