II.i High Altitude Operations

Question 1

What are the regulations pertaining to the use of supplemental oxygen on board a pressurized aircraft (91.211)?

Answer 1

B. No person may operate a civil aircraft of US registry with a pressurized cabin at flight altitudes above:

i. FL 250 unless at least a 10-minute supply of supplemental oxygen is available for each occupant of the aircraft for use in the event that a descent is necessitated by a loss of cabin pressure
a. This is in addition to oxygen required above
ii. FL 350, unless one pilot at the controls of the airplane is wearing and using an oxygen mask that is secured and sealed
a. The mask must supply oxygen at all times or automatically supply oxygen whenever the cabin pressure altitude of the airplane exceeds 14,000’ MSL
b. Exception: One pilot need not wear and use an oxygen mask while at or below FL 410 if there are two pilots at the controls and each pilot has a quick donning type of oxygen mask that can be placed on the face with one hand from the ready position within 5 seconds, supplying oxygen and properly secured and sealed
c. If one pilot leaves the controls the remaining pilot shall put on and use and oxygen mask until the other pilot has returned

Question 2

Describe a pressurization control system

Answer 2

The cabin is incorporated into a sealed unit capable of containing air under a higher pressure than the outside atmospheric pressure (Differential Pressure)

a. Differential Pressure - the difference between cabin pressure and atmospheric pressure normally expressed in psi (the higher the plane goes, the higher the differential to a limit)
b. Max differential pressure varies by make/model of plane
ii. Turbine powered aircraft – bleed air from the engine compressor section is used to pressurize the cabin
iii. In most light planes, the turbocharger’s compressor or engine driven pneumatic pump pressurizes the cabin
a. Compression heats the air, so it’s routed through a heat exchange unit before entering the cabin
iv. The cabin pressure control system provides pressure regulation, pressure relief and vacuum relief and the means for selecting the desired cabin altitude
a. A cabin pressure regulator, an outflow valve, and a safety valve are used to accomplish this

Question 3

Types of oxygen systems.

Answer 3

Continuous flow
Pressure demand
Diluter demand

Question 4

Continuous flow?

Answer 4

i. Most common in GA planes
ii. Usually for passengers and has a reservoir bag which collects oxygen from the system when exhaling
iii. Ambient air is added to the oxygen during inhalation after the reservoir oxygen supply is depleted
Exhaled air is released into the cabin

Question 5

Pressure demand?

Answer 5

Oxygen is supplied to the mask under pressure at cabin altitudes above 34,000’

i. Provide a positive pressure application of oxygen that allow the lungs to be pressurized with oxygen
iii. Some systems include the regulator on the mask to eliminate purging a long hose of air

Question 6

Diluter demand

Answer 6

Supply oxygen only when the user inhales through the mask

i. Depending on the altitude, the regulator can provide 100% oxygen or mix cabin air and the oxygen
ii. The mask provides a tight seal and can be used safely up to 40,000’

Question 7

Care and storage of high pressure oxygen bottles

Answer 7

Oxygen is usually stored at 1,800 – 2,200 psi

i. When the ambient temperature surrounding the cylinder decreases, pressure within will decrease
a. If a drop in indicated pressure is noted due to temperature, there is no reason to suspect depletion of the supply
ii. High pressure containers should be marked with the psi tolerance before filling to the pressure
C. Be aware of the danger of fire when using oxygen
i. Materials that are nearly fire proof in ordinary air may be susceptible to burning in pure oxygen
a. Oils and greases may catch fire if exposed to pure oxygen and cannot be in oxygen systems
ii. Smoking during any kind of oxygen equipment use is prohibited
iii. Before each flight, thoroughly inspect and test all oxygen equipment
D. Examine the equipment - available supply, operational check, and assure it is readily available
E. To assure safety, periodic inspections and servicing should be done

Question 8

Problems associated with rapid decompression and corresponding solutions.

Answer 8

Indications of a Rapid or Explosive Decompressurization
i. During explosive decompression, there may be noise and one may feel dazed for a second
a. Fog may occur and is the result of the rapid change in temperature and change of relative humidity
iii. Air will rush from the mouth and nose due to the escape from the lungs
iv. Differential air pressure on either side of the eardrum should clear automatically
v. Exposure to wind blast and extremely cold temperatures may occur
E. The primary danger of decompression is hypoxia
i. If proper use of oxygen equipment is not accomplished quickly unconsciousness may occur
F. Recovery from all types of decompression involves donning oxygen masks and an emergency descent
i. The top priority is reaching a safe altitude
a. Be aware, cold shock in piston engines can result from rapid high-altitude descents, cracking cylinders
b. The time to make a recovery before loss of useful consciousness is much less with an explosive decompression