High Altitude Operations

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Description: As you progress to more advanced planes, you will need to fly at higher altitudes and we need to know what to expect. 

 

Objective: To understand subjects pertaining to high altitude operations including environmental systems, emergency procedures, and normal operations 2. To be able to properly react to simulated emergencies specific to high altitude operation

 

Reference: PHAK, FAR part 91, AC 61-107 

 

Elements 

 

The High Altitude Flight Environment 

1.  As required by part 61, § 61.31, pilots who fly at altitudes at or above flight level (FL) 250 in a pressurized aircraft must receive training in the critical factors relating to safe flight operations under those circumstances.

1. That person must receive and logged ground training to satisfy the requirements of section 61.31(g)(1)(i-ix), 61.31(g)(2)(i-iii), and receives a logbook endorsement per section 61.31(g)(3).

2. These critical elements include knowledge of the special physiological and/or aerodynamic considerations that should be given to high-performance aircraft operating in the high-altitude environment.

3. Although the high altitude is defined as flight level 250, Class A starts at 18000 feet and oxygen requirements start much lower than that. 

4. FARs 91.215 all aircraft within the continental USA at above 10,000MSL must be equipped with an operable Mode C capable transponder unless operating at or below 2,500. 

 

1.Regulatory requirements for use of oxygen  91.211

Non-pressurized planes 

Pressurized aircraft: (Per FAR section 91.211 )No person may operate a civil aircraft of U.S. registry with a pressurized cabin—

1. At flight altitudes above flight level 250 unless at least a 10-minute supply of supplemental oxygen,

2. At flight altitudes above flight level 350 unless one pilot at the controls of the airplane is wearing and using an oxygen mask that is secured and sealed and that either supplies oxygen at all times or automatically supplies oxygen whenever the cabin pressure altitude of the airplane exceeds 14,000 feet (MSL), except that the one pilot need not wear and use an oxygen mask while at or below flight level 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.

3. f for any reason at any time it is necessary for one pilot to leave the controls of the aircraft when operating at flight altitudes above flight level 350, the remaining pilot at the controls shall put on and use an oxygen mask until the other pilot has returned to that crewmember's station.

 

2. Physiological hazards associated with high altitude operations. 

1. A. The human body functions normally from sea level to about 12,000’ MSL i. Brain oxygen saturation is at a level for normal function (Optimal functioning is 96% saturation) a. At 12,000’, oxygen saturation is approx 87%, which gets close to a performance affecting level b. Above 12,000’ oxygen saturation decreases and performance is affected. 

2. Hyperventilation: An increase in the rate and depth of breathing that exchanges gas in the lung beyond the volumes necessary to maintain normal levels of oxygen and carbon dioxide.

1. Symptoms perceived by an aviator who is hyperventilation include dizziness, lightheadedness, tingling, numbness, visual disturbances, and loss of coordination. 

3. Hypoxia: a state of oxygen deficiency in the blood, tissues, and cells sufficient to cause an impairment of body functions.

1. Hypoxic Hypoxia (Insufficient oxygen available to the lungs) 

2. Hyperemic Hypoxia (The blood cannot transport enough oxygen to the tissues/cells) 

3. Stagnant Hypoxia (Oxygen-rich blood isn’t moving to the tissues) 

4. Histotoxic Hypoxia (“Histo” refers to tissues or cells, and “Toxic” means poison)

1. All hypoxia will have these symptoms”

1. Cyanosis, Headache, Decreased reaction time/Impaired judgment, Euphoria, Visual Impairment, Drowsiness/Lightheaded or dizzy sensation, Tingling in fingers or toes and Numbness

2. Use supplemental oxygen or lower flight level. 

4. Time of Useful Consciousness

1. This is the period of time from interruption of the oxygen supply, or exposure to an oxygen-poor environment, to the time when an individual is no longer capable of taking proper corrective and protective action. 

2. The faster the rate of ascent, the worse the impairment, and the faster it happens. 

3. 

5. Altitude-Induced Decompression Sickness (DCS).

1. At sea level, the nitrogen pressure inside the body and outside of the body is in equilibrium.

2. When atmospheric pressure is reduced as a result of ascent, the equilibrium is upset.

3. This results in nitrogen leaving the body by passing from the cells, to the blood, and then out through the respiratory system. 

4. If the nitrogen is forced to leave the solution too rapidly because of a large partial pressure difference, bubbles may form, causing a variety of signs and symptoms.

5. There are two types of gas:

1. Trapped Gas. Expanding or contracting gas in certain body cavities during altitude changes can result in abdominal pain, toothache, or pain in ears and sinuses if the person is unable to equalize the pressure changes. Above 25,000 ft MSL, distention can produce particularly severe GI pain. 

2. Evolved Gas. When the pressure on the body drops sufficiently, nitrogen comes out of solution and forms bubbles, which can have adverse effects on some body tissues. 

6. Scuba diving and DCS

1.  SCUBA diving requires breathing air under high pressure. Under these conditions, there is a significant increase in the amount of nitrogen dissolved in the body

2. Following SCUBA diving, if not enough time is allowed to eliminate the excess nitrogen stored in the body, altitude DCS can occur during exposure to altitudes as low as 5,000 ft or less. 

3. Wait at least 12 hours for flights up to 8,000 ft

4. Wait at least 24 hours for flights above 8,000 ft. 

6. Vision deterioration 

1. Vision has a tendency to deteriorate with altitude; smoking worsens this effect.

2. The empty visual field caused by cloudless, blue skies during the day can cause inaccuracies when judging the speed, size, and distance of other aircraft.

7. Middle ear block

1. Ear pain and temporary reduction in the ability to hear due to difference differences from the outside and the ear cavity.

2. Due to the middle ear’s inability to equalize with the outside air pressure because the Eustachian tube might be blocked. 

8. Sinuses

1. Differences in pressure between the sinuses and the cockpit will create blockages which will lead to pain over the sinus area, toothache, or bloody mucus.

9. GI tract 

1. Foods such as veggies and beans produce gas, as the gas expands over altitude, you have to release it. 

10. Prolonged oxygen use 

1. can be harmful to health (100% aviation oxygen can create toxic symptoms if used for too long) 

2. The sudden supply of pure oxygen following decompression can often aggravate hypoxia. Therefore, oxygen should be taken gradually to build up in small doses 

3.  If symptoms are aggravated it may not mean the oxygen is not working, do not discard the oxygen supply and continue (this may even further increase the hypoxia) 

4.  Symptoms: bronchial cough, fever, vomiting, nervousness, irregular heartbeat, lowered energy

 

3. Characterization of a pressurized airplane and various types of supplemental oxygen systems. 

1. A. Cabin pressurization is the compression of air to maintain a cabin altitude lower than the flight altitude. 

1. This removes the need for full-time use of supplemental oxygen ii. A cabin pressure altitude of approx 8,000’ is maintained and prevents rapid changes of cabin altitude that may be uncomfortable or cause injury to passengers/crew (prevents against hypoxia)

2. How it Works. 

1. The cabin, flight and baggage compartments are incorporated into a sealed unit capable of containing air under higher pressure than the outside atmospheric pressure (Differential Pressure) 

2. 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).

3. Turbine powered aircraft uses bleed air from the engine compressor section is used to pressurize the cabin. 

1. Compression heats the air, so it’s routed through a heat exchange unit before entering the cabin

3. Cabin air pressure safety valves

1. The cabin pressure control system provides pressure regulation, pressure relief, and vacuum relief and the means for selecting the desired cabin altitude

1. Pressure relief valve: makes sure the cabin pressure is not over. 

2. Vacuum relief: If ambient pressure is higher than cabin pressure, it allows some ambient pressure to come in. 

3. Dump valve: Releases all cabin pressure to outside. 

4. Instruments for pressurization system 

1. Cabin differential pressure gauge indicates the difference between inside and outside pressure

2. Cabin Altimeter shows the altitude inside the airplane

3. Cabin Rate of Climb/Descent

5. Types of supplemental oxygen - Most high altitude planes are equipped with some sort of fixed or portable oxygen system. It consists of a container , regulator, mask, and pressure gauge 

1. Oxygen Masks

1. Nasal cannulas

1. Continuous flow devices 

2. Personal comfort

3. Use for up to 18,000 feet service altitude because of the risk of reducing oxygen-blood saturation levels if one breathes through the mouth too much. 

2. Oral-nasal-re-breather

1. Simple, common, and cheapest

2. It has an external plastic bag that inflates very time you exhale to store exhaled air so it may be mixed with 100 percent oxygen from the system.

3. Useable up to 25,000 feet

3. Quick-don mask

1. Able to be put on within five seconds for quick crew access

2. Rated up to 40,000 feet

4. Airline drop-down units

1. Uses a series of one-way ports that allow a mixture of 100 percent oxygen and cabin air into the mask

2. Exhalation is vented to the atmosphere so the bag does not inflate.

3. Used for emergencies up to 40,000 feet

4. 

2. Oxygen delivery systems

1. Continuous flow

1. This system delivers a continuous flow of oxygen from the storage container

2. Very economical system that it doesn’t need complicated masks or regulators to work

3. Wasteful since the flow of oxygen is constant 

4. Up to 28,000 feet

2. Diluter Demand

1. Compensates for the shortcomings of the continuous flow systems by giving the user on demand during inhalation and stops the flow when the demand ceases during exhalation

2. Also, the incoming oxygen is diluted with cabin air and provides the proper percentage of oxygen. 

3. Up to 40,000 feet 

3. Pressure Demand

1. It provides oxygen under positive pressure which is a forceful oxygen flow that is intended to slightly over-inflate the lungs.

 

4. Importance of aviator’s breathing oxygen 

1. Aviators oxygen is specified at 99.5% pure oxygen and not more than .005mg of water per liter. 

2. It is recommended that aviator’s breathing oxygen be used at all times, medical and industrial oxygen may not be safe 

1. Medical oxygen has too much water, which can collect in various parts of the system and freeze 

1. Freezing may reduce/stop the flow of oxygen 

3. Industrial oxygen is not intended for breathing and may have impurities in it (metal shavings, etc.)

 

5. Care and storage of high-pressure oxygen bottles

1. Pilots should aware of the danger of fire when using oxygen.

1. Materials that are nearly fireproof in ambient air may be susceptible to combustion in oxygen. 

2. Oils and grease will ignite if exposed to oxygen and cannot be used for sealing the valves and fittings of oxygen equipment. 

3. Smoking is strictly prohibited. 

4. Inspection should include a thorough examination of the: 

1. Pilots should inspect: 

1. Available supply

2. An operational check of the system

3. Assurance that the supplemental oxygen is readily available 

4. Visual inspection of the mask and tubing for tears, cracks, or deterioration. 

5. Regulator for valve and lever condition

6. Oxygen quantity

7. Location and functions of oxygen pressure gauges, flow indicators, and connections

8. Masks should be donned and tested

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

1. When the ambient temperature surrounding the cylinder decreases, the pressure within will decrease

2. If a drop in indicated pressure is noted due to temperature, there is no reason to suspect depletion of the supply 

3. High-pressure containers should be marked with the psi tolerance before filling to the pressure

 

6.Problems associated with rapid decompression and corresponding solutions 

 

1. Decompression - the inability of the aircraft’s pressurization system to maintain its designed pressure schedule. Decompression can be caused by a malfunction of the system itself or structural damage to the aircraft. 

1.  Rapid Decompression - A change in cabin pressure where the lungs can decompress faster than the cabin. The risk of lung damage is significantly lower in this decompression compared to explosive decompression. 

2. Explosive Decompression - A change in cabin pressure faster than the lungs can decompress. Most authorities consider any decompression that occurs in less than 0.5 seconds as explosive and potentially dangerous. This type of decompression is more likely to occur in small volume pressurized aircraft than in large pressurized aircraft and often results in lung damage. To avoid potentially dangerous flying debris in the event of explosive decompression, properly secure all loose items such as baggage and oxygen cylinders. 

3. Slow Decompression A gradual or slow decompression is dangerous because it may not be detected. Automatic visual and aural warning systems generally provide an indication of a slow decompression. 

2. Associated problems 

1.  the cabin will fill with fog, dust, flying debris

2. Fog is the result of the rapid change in temperature and change of relative humidity

3.  Air will rush from the mouth and nose due to the escape from the lungs

4. Exposure to wind blast and extremely cold temperatures may occur

5. Hypoxia 

3. Solutions 

1. Supplemental oxygen 

2. Descend to a lower altitude

 

7. The fundamental concept of cabin pressurization 

1. Cabin, flight compartments, and baggage compartments are incorporated into a sealed unit capable of containing air under a pressure higher than outside atmospheric 

2. Cabins are usually maintained at 8,000 ft. 

3. Prevents stale air and eliminates odor 

4. Protects the occupants from hypoxia. 

 

8. Operation of a cabin pressurization system 

1. On aircraft powered by turbine engines, bleed air from the engine compressor section is used to pressurize the cabin

1. Exhausts from the engine is used to spin a turbine which powers a compressor that compresses bleed air then send its to a cooler and then it is allowed to go to the cabin 

2. Air is released from the fuselage by a device called an outflow valve. 

3. Cabin pressure control system provides cabin pressure regulation, pressure relief, vacuum relief, and the means to select the desired cabin altitude.

1. Cabin pressure regulator controls cabin to a selected value in the isobaric range and limits cabin pressure to a preset differential value in the differential range

2. Differential control is used to prevent the maximum differential pressure

3. Pressure relief prevents cabin pressure from exceeding a predetermined differential pressure above ambient pressure. 

4. Vacuum relief ambient pressure from exceeding cabin pressure by allowing external air to come in

5. Dump valves dump cabin air into the atmosphere