Par 2-5 Page 9 (NM) or vertical wind shear of 6 kts or greater per 1,000 ft usually indicate moderate to severe turbulence and should be avoided.
d. Clear Air Turbulence (CAT). CAT is a meteorological phenomenon associated with high-altitude winds. This high-level turbulence occurs where no clouds are present and can take place at any altitude (normally higher than 15,000 ft above ground level (AGL)), although it usually develops in or near the jet stream where there is a rapid change in temperature. CAT is generally stronger on the polar side of the jet and greatest during the winter months. Causes of CAT are wind shear, convection currents, mountain waves, strong low pressures aloft, or other obstructions to normal wind flow. CAT is difficult to forecast because it gives no visual warning of its presence and winds can carry it far from its point of origin. Pilot Weather Reports (PIREP) are one of the best methods of receiving timely and accurate reports on icing and turbulence at high altitudes.
e. Clouds and Thunderstorms. Cirrus and cirriform clouds are high-altitude clouds composed of ice crystals. Cirrus clouds are found in stable air above 30,000 ft MSL in patches or narrow bands. Cirriform clouds, such as the white clouds in long bands against a blue background known as cirrostratus clouds, generally indicate some type of system below.
Cirrostratus clouds form in stable air as a result of shallow convection currents and also may produce light turbulence. Clouds with extensive vertical development (e.g., towering cumulus and cumulonimbus clouds) indicate a deep layer of unstable air and contain moderate to heavy turbulence with icing. The bases of these clouds are found at altitudes associated with low to middle clouds but their tops can extend up to 60,000 ft MSL or more.
NOTE: Cumulonimbus clouds are thunderstorm clouds that present a particularly severe hazard that pilots should circumnavigate. Hazards associated with cumulonimbus clouds include embedded thunderstorms, severe or extreme turbulence, lightning, icing, and dangerously strong winds and updrafts.
f. Icing. Icing at high altitudes is not as common or extreme as it can be at low altitudes.
When it does occur, the rate of accumulation at high altitudes is generally slower than at low altitudes. Rime ice is generally more common at high altitudes than clear ice, although clear ice is possible. Despite the composition of cirrus clouds, severe icing is generally not a problem although it can occur in some detached cirrus. It is more common in tops of tall cumulus buildups, anvils, and over mountainous regions.
2-6. FLIGHT PLANNING AND NAVIGATION.
a. Flight Planning.
(1) Operational Considerations. Careful flight planning is critical to safe high-altitude flight. Pilots must consider pressurization system settings, particularly on takeoff, climb, and descent to assure operation in accordance with the manufacturer’s recommendations. They must also consider fuel management, reporting points, weather briefings, direction of flight, airplane performance charts, aircraft systems, and procedures, high-speed winds aloft, and oxygen
Page 10 Par 2-6 duration charts. When possible, additional oxygen should be provided to allow for emergency situations. Breathing rates increase under stress and extra oxygen could be necessary.
(2) Altitude Considerations. Flight planning should take into consideration factors associated with altitudes that pilots will transit while climbing to or descending from the high altitudes (e.g., airspeed limitations below 10,000 ft MSL, airspace, and minimum altitudes).
Westward flights should generally be made away from the jet stream to avoid the strong headwind, and eastward flights should be made in the jet stream when possible to increase ground speed. Ground speed checks are particularly important in high-altitude flight. If fuel runs low because of headwinds or poor flight planning, a decision to fly to an alternate airport should be made as early as possible to allow time to replan descents and advise air traffic control (ATC).
b. Knowledge of Aircraft. Complete familiarity with the aircraft systems and limitations is extremely important. For example, many high-altitude airplanes feed from only one fuel tank at a time. If this is the case, it is important to know the fuel consumption rate to know when to change tanks. This knowledge should be made part of the preflight planning and should have its accuracy confirmed regularly during the flight.
c. Gradual Descents. Pilots should plan gradual descents from high altitudes in advance to prevent excessive engine cooling and provide passenger comfort. They should comply with the manufacturer’s recommendations found in the AFM, especially regarding descent power settings, to avoid stress on the engines. Although most jets can descend rapidly at idle power, light twin airplanes require some power to avoid excessive engine cooling, cold shock, and metal fatigue. ATC does not always take aircraft type into consideration when issuing descent instructions. It is the pilot’s responsibility to fly the airplane in the safest manner possible. Cabin rates of descent are particularly important and should generally not exceed 500 or 600 ft/min.
Before landing, cabin pressure should be equal to ambient pressure or inner ear injury can result.
If delays occur en route, pilots should adjust descents.
d. Weather Charts. Before beginning a high-altitude flight, pilots should consult all weather charts, including those designed for low levels. High-altitude flight allows a pilot to over-fly most adverse weather, but pilots must consider low altitude weather for arrival, departure, and en route emergencies that require an immediate diversion.
e. Types of Weather Charts. Weather charts that provide information on high-altitude weather include:
• Constant pressure charts provide information on pressure systems, temperature, winds, and temperature/dewpoint spread at the 850 millibar (mb), 700 mb, 500 mb, 300 mb, and 200 mb levels (the five charts are issued every 12 hours).
• Prognostic charts, which provide forecast winds, temperature, and expected movement of weather over the 6-hour valid time of the chart.
• Observed tropopause charts, which provide jet stream, turbulence, and temperature/wind/pressure reports at the tropopause over each station.
• Tropopause wind prognostic charts, which are helpful in determining jet stream patterns and the presence of CAT and wind shear.
Par 2-6 Page 11
• Tropopause height vertical wind shear charts, which are helpful in determining jet stream patterns and the presence of CAT and wind shear. Dashed lines indicate wind shear.
f. Navigation. Specific charts are available for flight at FL 180 and above. En route high-altitude charts delineate the jet route system, which consists of routes established from FL 180 up to and including FL 450. The very high frequency Omnidirectional Range (VOR) airways established below FL 180 found on low-altitude charts must not be used at FL 180 and above. High-altitude jet routes are an independent matrix of airways, and pilots must possess the appropriate en route high-altitude charts before transitioning to the FLs.
(1) Jet Routes. Jet routes in the United States are predicated solely on VOR or VHF Omnidirectional Range Collocated and Tactical Air Navigational (VORTAC) navigation facilities, except in Alaska where some are based on low/medium frequency NAVAIDs. All jet routes are identified by the letter “J” followed by the airway number.
(2) Q-Routes. The U.S. and Canada use “Q“ as a designator for RNAV routes.
Q-routes routes are designed for RNAV or RNP capable aircraft. One benefit of this system is that aircraft with RNAV or RNP capability can fly safely along closely spaced parallel flight paths on high density routes, which eases airspace congestion.
(3) Reporting Points. Designated reporting points must be used by flights using the jet route unless otherwise advised by ATC. Pilots may conduct flights above FL 450 on a point-to-point basis, using the facilities depicted on the en route high-altitude chart as navigational guidance. Area Navigation (RNAV) routes, using either random or fixed waypoints, are also used for direct navigation at high altitudes. These routes are based on RNAV capability between waypoints defined in terms of latitude/longitude coordinates, degree-distance fixes, or offsets from established routes or airways at a specified distance and direction. Radar monitoring by ATC is required on all random RNAV routes.
g. NAVAIDS. VOR, distance measuring equipment (DME), and TACAN depicted on high-altitude charts are designated as Class H NAVAIDs, signifying that their standard service volume is from 1,000 ft AGL up to and including 14,500 ft AGL at radial distances out to 40 NM; from 14,500 ft AGL up to and including 60,000 ft AGL at radial distances out to 100 NM; and from 18,000 ft AGL up to and including 45,000 ft AGL at radial distances out to 130 NM. See Figure 2-1, Standard High-Altitude Service Volume, for an illustration of the high-altitude service volume. Ranges of non-directional beacon (NDB) service volumes are the same at all altitudes.
Page 12 Par 2-6 FIGURE 2-1. STANDARD HIGH-ALTITUDE SERVICE VOLUME
2-7. PHYSIOLOGICAL TRAINING. To ensure safe flights at high altitudes, pilots of high-altitude aircraft must understand the physiological effects of high-altitude flight and the effect of hypoxia on an individual’s ability to perform complex tasks in a changing environment.
Additional physiological training information, including locations and application procedures for attending an altitude chamber, can be found in paragraph 2-8. Although not required, altitude chamber training is highly recommended for all pilots.
a. Physics of the Atmosphere. The combined weight, or force, of all gases in the atmosphere at any given point gives us our atmospheric pressure. As you ascend from sea level, the atmospheric pressure will correspondingly drop. As atmospheric pressure drops, the air becomes less dense. The primary reason for this phenomenon lies in the kinetic nature of atoms and molecules. Molecules, especially those of a gas, are in a constant state of motion. As pressure around the molecules is reduced, the molecules will travel further apart. This explains why air becomes less dense as altitude increases, and accounts for gas expansion. Since air is a mixture of gases, it is subject to the laws that govern all gases. Table 2-1, Gas Laws and Their Effect on the Human Body, explains the effects of reduced barometric pressure and its interplay on the human body.
TABLE 2-1. GAS LAWS AND THEIR EFFECT ON THE HUMAN BODY
GAS LAW EXPLANATION AVIATION APPLICATION Graham’s Law Law of gaseous diffusion
A gas will diffuse from an area of high concentration to an area of low concentration.
TRANSFER OF GAS IN BODY This law explains the transfer of gases between the atmosphere and the lungs, the lungs and the blood, and the blood and the cell.
Par 2-7 Page 13
GAS LAW EXPLANATION AVIATION APPLICATION Boyle’s Law P1 = V2 P2 V1
A volume of a gas is inversely proportional to the pressure to which it is subjected with the temperature remaining constant.
TRAPPED GAS This law explains how pressure change allows the gas to expand and contract in body cavities (ears, sinuses, and gastrointestinal (GI) tract) with increasing and decreasing altitude.
Dalton’s Law PT=P1+P2+…PN The total pressure of a mixture of gas is equal to the sum of the partial pressure of each gas in the mixture.
HYPOXIA This law explains how ascent to altitude reduces the total atmospheric pressure, thus reducing each of the partial pressures associated with the total atmospheric pressure.
Henry’s Law P1 = A1 P2 A2
The amount of gas dissolved in solution varies directly with the pressure of that gas over the solution.
DECOMPRESSION SICKNESS This law explains why nitrogen in the body comes out of solution forming bubbles that cause decompression sickness. As altitude increases, pressure decreases and nitrogen will attempt to leave the body and equalize with the surrounding environment. If pressure change is too rapid, the excess nitrogen may form a bubble(s).
Charles’ Law V1 = T1 V2 T2 The pressure of a gas is directly proportional to its temperature.
This gas law has no physiological bearing since body temperature is a constant 98.6°F.
b. Respiration. When we are exposed to a high altitude environment, our ability to obtain and utilize oxygen is dramatically affected. External respiration is the exchange of gases between the lungs and the surrounding atmosphere. With each breath (about half a liter of air), we inhale
2.79 x 1021 oxygen molecules.
(1) Partial Pressure of Oxygen. The partial pressure of oxygen is approximately 20 percent of the total atmospheric pressure. At sea level, this would be about 152 millimeters of mercury (mmHg) of pressure (20 percent of the total atmospheric pressure of 760 mmHg). When a breath is drawn into the lungs, one would expect the partial pressure of oxygen to remain at Ground Level 17,000 MSL
Page 14 Par 2-7 152 mmHg. However, the lungs contain other gases that exert a constant pressure (water vapor at 47 mmHg and carbon dioxide at 40 mmHg). These gases tend to displace part of the oxygen, reducing the partial pressure of oxygen at the air sac (alveoli) level to 102 mmHg.
(2) Oxygen and Carbon Dioxide Diffusion in the Blood. Oxygen and carbon dioxide move into and out of the blood in the lungs in accordance with Graham’s Law, which states: “An area of high gaseous pressure will exert force towards an area of low gaseous pressure.” This will cause gases to move back and forth across a gas permeable membrane (such as the air sacs).
At sea level, the high partial pressure of oxygen (102 mmHg) diffuses through the air sac wall and into the blood (see Figure 2-2, Blood Cells and Alveoli). This in turn raises the partial pressure of oxygen in venous blood (blood that has left the cells and therefore is low in oxygen) from 40 mmHg to 102 mmHg. At the same time this is happening, the high pressure of carbon dioxide (approximately 47 mmHg) in the blood will cause some of the carbon dioxide to diffuse into the air sacs where carbon dioxide pressure is a constant 40 mmHg. This principle also applies to internal respiration (the exchange of gases from the blood to the cells). The high partial pressure of oxygen in arterial blood causes the oxygen to move from the blood into the cells. Due to cellular metabolism, the high partial pressure of carbon dioxide in the cell will cause it to diffuse into the blood for transport to the lungs.
(3) Atmospheric Areas and Normal Body Function. The human body functions normally in the atmospheric area extending from sea level to 12,000 ft MSL. In this range, brain oxygen saturation is at a level that allows for normal functioning. Optimal functioning is 96 percent saturation. At 12,000 ft MSL, brain oxygen saturation is approximately 87 percent, which begins to approach a level that could affect human performance. Although oxygen is not required below on 12,500 ft MSL when operating in accordance with part 91, we recommend its use when flying unpressurized above 10,000 ft MSL during the day and above 5,000 ft MSL at night when the eyes become more sensitive to oxygen deprivation.
FIGURE 2-2. BLOOD CELLS AND ALVEOLI
c. Trapped Gas. Gases readily expand with any decrease in pressure. Gas expands in accordance with Boyle’s Law, which states: “A volume of a gas is inversely proportional to the pressure to which it is subjected, temperature remaining constant.” From this law it is apparent that if you reduce the pressure, as you ascend to altitude, gases increase in volume and then decrease in volume on descent.
Red Blood Cells Alveoli
Par 2-7 Page 15
(1) The human body has several cavities that contain varying amounts of gas. Most of these cavities have an opening that will allow the gas to enter and escape. If the opening is reduced in size or closed, then the gas is trapped. Once trapped, it is still subject to gas expansion and compression in accordance with Boyle’s Law. The result of having changes in gas volume within these cavities without equalization will usually be pain. Table 2-2, Trapped Gas Issues, gives examples of body areas that may be affected by trapped gas during the specified phases of flight.
(2) Table 2-3, In-Flight Treatment of Trapped Gas Emergencies, gives the recommended procedures for in-flight treatment of trapped gas emergencies.
Page 16 Par 2-7 TABLE 2-2. TRAPPED GAS ISSUES
BODY AREA PROBLEM PHASE
OF FLIGHT
PHYSIOLOGY
MIDDLE EAR
DESCENT On ascent, the air and pressure of expanding gases will escape via the eustachian tube. The base of each eustachian tube is collapsed, which acts as a one-way valve to allow gases and liquids to escape and not travel up to the middle ear. On descent, the gas is naturally trapped. Because of the increasing pressure on descent, this pressure will need to be equalized or an ear block will result.
SINUSES
DESCENT or ASCENT (rare) The maxillary sinuses that sit under the cheekbones and the frontals that lie under the eyebrows have an unobstructed opening that will allow gas to enter and escape. In the event of an upper respiratory infection (URI), the openings will be swollen and possibly closed allowing no route for the gas and pressure to equalize, resulting in a sinus block.
TEETH
ASCENT A tooth block is very rare. They can occur if you have had a recent cavity filling. If there is any airspace trapped between the filling and the pulp of the tooth, it will expand on ascent and cause pain.
GI
ASCENT The GI tract will always contain a varying amount of gas. This gas is usually a result of the digestion process and can escape by either flatulation or belching. If the gas expands, as in unpressurized flight to altitude, and is not allowed to escape, it could result in pain and possible syncope (fainting).
LUNGS
DECOMPRESSION Gas in the lungs will normally enter and escape via the trachea. If the breath is held during a rapid increase in altitude, the gas within the lungs will expand in accordance with Boyle’s Law, but have no pathway to escape. This could cause possible lung damage.
Par 2-7 Page 17 TABLE 2-3. IN-FLIGHT TREATMENT OF TRAPPED GAS EMERGENCIES
AILMENT SYMPTOMS TREATMENT Ear Block Can start out as a full feeling that will progress to pain. Pain increases with descent. Can also cause vertigo.
• Level off from descent.
• Try ear-clearing maneuvers such as valsalva, aviators jaw jut, yawn, or swallow.
• Ascend and try ear-clearing again.
• If there is no relief, land A.S.A.P.
Sinus Block Intense pain under the cheekbones and in the upper teeth (maxillary). Intense pain under eyebrows and in corner of the eyes (frontal).
• Level off from descent.
• Try the valsalva maneuver.
• Ascend and try sinus-clearing again.
• If there is no relief, land A.S.A.P.
Tooth Block A pain in a single tooth where the pain increases with a corresponding increase in altitude.
• Level off from ascent.
• If there is no relief, land A.S.A.P. and see a dentist.
GI Tract Progressively increasing pain in the abdominal area with a corresponding increase in altitude.
• Try to pass the gas through flatulating or belching.
• If there is no relief, immediate descent.
d. Physiological Problems at Increased Altitudes.
(1) Hypoxia. Hypoxia is a state of oxygen deficiency in the blood, tissues, and cells sufficient to cause an impairment of body functions. Anything that impedes the arrival or utilization of oxygen to the cell places the body in a hypoxic state. All cells require oxygen to function. The central nervous system (made up of the brain and spinal cord) demands a great deal of oxygen (approximately 20 percent of all oxygen that you inhale feeds the brain). If the oxygen supply to the body is reduced, the brain will be one of the first organs to be affected, with the higher reasoning portions of the brain showing degraded function first. This means that judgment and cognitive skills diminish from the very start. There are many conditions that can interrupt the normal flow of oxygen to the cells. Table 2-4, Hypoxia Types, describes the various levels at which hypoxia can occur:
(2) Hyperventilation. Hyperventilation is defined as 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. Hyperventilation will result in disturbances in the acid-base balance in the blood, and eventually the brain as the levels of carbon dioxide in the lungs fall.
The signs and symptoms of hyperventilation are easily confused with those of hypoxic hypoxia.
Because hyperventilation occurs as an carly adaptive mechanism to hypoxia at altitude, it becomes even more difficult to differentiate between the two conditions. Symptoms perceived by an aviator who is hyperventilation include dizziness, lightheadedness, tingling, numbness, visual disturbances, and loss of coordination. The treatment of hyperventilation requires a voluntary reduction in the rate and depth of ventilation. Because hypoxia and hyperventilation are so similar and both can incapacitate so quickly, the recommended treatment procedures for aviators is to correct both problems simultaneously: (1) administer 100% oxygen under pressure; (2) reduce the rate and depth of breathing: (3) check the oxygen equipment to ensure proper functioning: and (4) descend to a lower altitude where hypoxia is unlikely to occur.
Page 18 Par 2-7 TABLE 2-4. HYPOXIA TYPES Common Name Location of Impediment Explanation Hypoxic (Altitude) Hypoxia Lungs Any condition that interrupts the flow of O2 into the lungs. This is the type of hypoxia encountered at altitude due to the reduction of the partial pressure of O2.
Hypemic Hypoxia Blood
Any condition that interferes with the ability of the blood to carry oxygen, such as:
• Anemia.
• Bleeding.
• Carbon monoxide poisoning.
• Smoking.
• Certain prescription drugs.
Stagnant Hypoxia Blood Transport Any situation that interferes with the normal circulation of the blood arriving to the cells. Heart failure, shock, and positive G-forces will bring about this condition.
Histotoxic Hypoxia Cell Any condition that interferes with the normal utilization of O2 in the cell. Alcohol, narcotics, and cyanide all can interfere with the cell’s ability to use the oxygen in support of metabolism.
(a) Hypoxic (Altitude) Hypoxia. The cause of this type of hypoxia is an insufficient partial pressure of oxygen in the inhaled air resulting from reduced oxygen pressure in the atmosphere at altitude. Altitude hypoxia poses the greatest potential physiological hazard to a flightcrew member when at altitude. Supplemental oxygen will combat hypoxic hypoxia within seconds. Check your oxygen systems periodically to ensure an adequate supply of oxygen and that the system is functioning properly. Perform this check frequently with increasing altitude. If supplemental oxygen is not available, initiate an emergency descent to an altitude below 10,000 ft MSL.
WARNING:
If hypoxia is suspected, immediately don oxygen mask and breathe 100 percent oxygen slowly. Descend to a safe altitude. If supplemental oxygen is not available, initiate an emergency descent to an altitude below 10,000 ft MSL. If symptoms persist, land as soon as possible.
(b) Hypemic Hypoxia. This type of hypoxia is defined as a reduction in the oxygen-carrying capacity of the blood. Hypemic hypoxia is caused by a reduction in circulating red blood cells (anemia) or contamination of blood with gases other than oxygen.
1. The most common cause is smoking, but carbon monoxide poisoning due to a leak in the exhaust system for the engine is also a consideration. Pilots should take into consideration the effect of smoking on altitude tolerance when determining appropriate cabin
Par 2-7 Page 19 pressures. If heavy smokers are among the crew or passengers, a lower cabin altitude should be set because physiologic altitudes for smokers are generally much higher than actual altitudes. For example, a smoker’s physiological altitude at sea level is approximately 7,000 ft MSL. Twenty thousand ft actual altitude for a nonsmoker would be equivalent to a physiological altitude of 22,000 ft MSL for a smoker. The smoker is thus more susceptible to hypoxia at lower altitudes than the nonsmoker.
2. Hypemic hypoxia is corrected by locating and eliminating the source of the contaminating gases. A careful preflight of heating systems and exhaust manifold equipment is mandatory. If symptoms persist, ventilate the cabin, land as soon as possible, and seek medical attention, because the symptoms may be indicative of carbon monoxide poisoning.
WARNING:
If hypoxia is suspected, immediately don oxygen mask and breathe 100 percent oxygen slowly. Descend to a safe altitude. If supplemental oxygen is not available, initiate an emergency descent to an altitude below 10,000 ft MSL. If symptoms persist, land as soon as possible.
(c) Stagnant Hypoxia. This is a less common form of hypoxia. It is due to inadequate blood flow to the tissues. Causes include heart failure, shock, prolonged positive pressure breathing, and excessive G-forces.
WARNING:
If hypoxia is suspected, immediately don oxygen mask and breathe 100 percent oxygen slowly. Descend to a safe altitude. If supplemental oxygen is not available, initiate an emergency descent to an altitude below 10,000 ft MSL. If symptoms persist, land as soon as possible.
(d) Histotoxic Hypoxia. This is the inability of the body’s cells to use oxygen because of impaired cellular respiration. Alcohol or drug use can cause this type of hypoxia. The only method of avoiding this type of hypoxia is to abstain, before flight, from alcohol or drugs that are not approved by a flight surgeon or an Aviation Medical Examiner (AME).
WARNING:
If hypoxia is suspected, immediately don oxygen mask and breathe 100 percent oxygen slowly. Descend to a safe altitude. If supplemental oxygen is not available, initiate an emergency descent to an altitude below 10,000 ft MSL. If symptoms persist, land as soon as possible.
Page 20 Par 2-7
(e) Hypoxia Signs and Symptoms.
1. Signs of hypoxia can be detected in an individual by an observer. Signs aren’t a very effective tool for hypoxic individuals to use to recognize hypoxia in themselves.
Symptoms of hypoxia are the sensations a person can detect while in a hypoxic state. Personal symptoms of hypoxia are as individual as the person experiencing them. A group of people who are hypoxic will, a majority of the time, get the same symptoms. However, the symptoms will appear in a different order and in varying intensities. The greatest benefit in hypoxia training in an altitude chamber is that the order and the intensity of your symptoms will usually remain constant over the years. Therefore, familiarity with one’s own hypoxia “signature” will facilitate the recognition of a hypoxic state during flight. Table 2-5, Common Hypoxia Signs and Symptoms, lists some of the more common signs and symptoms of hypoxia.
TABLE 2-5. COMMON HYPOXIA SIGNS AND SYMPTOMS
SIGNS SYMPTOMS Rapid Breathing Cyanosis (bluing effect of the skin) Poor Coordination Lethargy Executing Poor Judgment Sweating Trembling Myoclonic (Muscle) Spasms Air Hunger Fatigue Nausea Headache Dizziness Hot and Cold flashes Tingling Visual Impairment Euphoria
2. Of the listed symptoms, visual impairment is probably the least reliable.
Your visual field will be affected, but at such a slow rate that it could go unnoticed. Generally, symptoms will appear before unconsciousness occurs. Except for possible headache and nausea, there are no other uncomfortable symptoms. Of all the symptoms, euphoria (a false sense of well-being) is probably the most dangerous. Furthermore, in most cases, hypoxia onset is very insidious. Any preoccupation with flying duties could be enough of a distraction to allow the hypoxia to progress beyond the point of self-help.
WARNING:
A common misconception among pilots is that it is easy to recognize the symptoms of hypoxia and to take corrective action before becoming seriously impaired. While this concept may be appealing in theory, it is both misleading and dangerous for crewmembers.
3. While other significant effects of hypoxia usually do not occur in a healthy pilot in an un-pressurized aircraft below 12,000 ft MSL, there is no assurance that this will always be the case. Furthermore, the altitude range of impairment due to hypoxia is best described as a continuum; there is no definitive altitude at which the effects of hypoxia begin or