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e. 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 VOR Collocated Tactical Air Navigation (VORTAC) 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 United States and Canada use “Q” as a designator for Area Navigation (RNAV) routes. Q-routes routes are designed for RNAV- or Required Navigation Performance (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. 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.
f. NAVAIDs. VOR, distance measuring equipment (DME), and Tactical Air Navigation Aids (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 Radio Homing 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.
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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
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(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) 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 early 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 percent 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.
(2) 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.
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.
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(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 unpressurized 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
Par 2-7 Page 21 end. To mitigate the risk associated with these variations, if hypoxia is suspected, a descent to altitudes below 10,000 ft MSL is recommended.
(f) Preventative Measures Against Hypoxia.
1. A common technique for aviators to monitor themselves for hypoxia is the use of finger pulse oximeters that report the degree of hemoglobin oxygen saturation as a percent. This value is useful in predicting the partial pressure of oxygen available to drive oxygen into the cells.
CAUTION:
The FAA cautions against relying on pulse oximeters as the sole indicator of hypoxia because:
• Waiting for the percent oxygen saturation levels reported by the pulse oximeter to fall before taking action may result in a level of hypoxia sufficient to cause impairment.
• Hemoglobin oxygen saturation in blood passing through the finger may not reflect true oxygen availability to the brain because of reductions in brain blood flow resulting from hyperventilation (a response to hypoxia).
2. The following are recommended actions to reduce the chance of hypoxia.
• Fly at an altitude where oxygen is not required.
• Fly in a pressurized cabin.
• Fly in accordance with current regulations in reference to the use of supplemental oxygen.
NOTE: The FAA recommends that on any unpressurized flight to or above 10,000 ft in the day, or above 5,000 ft at night, supplemental oxygen should be used.
(g) Treatment for Hypoxia. Hypoxia, under most situations, will be insidious in its onset, which gives it its dangerous nature. Because of the rapid breathing associated with hypoxia, you must slow your breathing rate to prevent hyperventilation. Recognition and the immediate execution of emergency procedures for decompression are the most important factors that dictate the crew’s ability to survive. If hypoxia is suspected, immediately don an oxygen mask and breathe 100 percent oxygen slowly. Descend to a safe altitude. Once hypoxia is detected and 100 percent oxygen is administered, recovery usually occurs in a matter of seconds.
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. The common emergency procedures follow in Table 2-6, Common Emergency Procedures for Hypoxia.
Page 22 Par 2-7 TABLE 2-6. COMMON EMERGENCY PROCEDURES FOR HYPOXIA DON MASK In 5 seconds or less. Check for flow. Breathe 100 percent oxygen.
DESCEND Preferably below 10,000 ft.
LAND A.S.A.P At nearest suitable installation where appropriate medical help can be found.
e. Decompression in Pressurized Aircraft. Even though there are numerous advantages to pressurized flight, there will always be one major disadvantage—possible loss of pressurization.
(1) Rate of Decompression. Factors that dictate how fast an aircraft will decompress are:
(a) Size of Opening. With all other factors equal, the larger the opening, the faster the pressure will travel out of the aircraft.
(b) Size of Cabin. With all other factors equal, the smaller the cabin, the faster the pressure will depart.
(c) Pressure Differential. With all other factors equal, greater pressure differential means slower decompression.
(d) Pressure Ratio. When cabin pressurization is lost, aircraft compressors will continue to operate. The rate at which the compressed air comes in dictates how fast pressure is lost.
(e) Altitude. Higher altitude results in a faster decompression due to less resistance to the air leaving the aircraft.
(2) Phenomena Associated with Decompressions. These decompression phenomena are very common to rapid and explosive decompressions. However, during a slow decompression, the phenomena below may not be evident. Furthermore, the insidious nature of hypoxia and depression of mental function decreases the ability to recognize the emergency and undertake appropriate recovery procedures. For this reason, slow decompressions are the most dangerous, and the aviator must always be on guard against this insidious threat.
(a) Noise. Noise can come from a leaky door seal, a window departing, a breach of structural integrity, or from the aircraft’s alarm system.
(b) Fog. On smaller airframes (Learjets, Citations, Falcons) the fog could fill the aircraft.
(c) Flying Debris, Dust, and Dirt. If there is a large opening, anything not secured down will move towards the opening. These items could cause injury.