Study guide
17.1 Hypoxia, Hyperventilation, and Carbon Monoxide
FAA Private Pilot — Airplane PAR
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1 Introduction & Exam Overview
1.1 Current Exam Facts 1.2 ACS Codes, the AKTR, and How to Use This Guide
2 Pilot Qualifications & Medicals
2.1 Eligibility, Training, and Knowledge-Test Authorization 2.2 Private Pilot Privileges and Limitations 2.3 Medical Certificates, Duration, and Disqualification 2.4 BasicMed (14 CFR 61.113(i) and Part 68)
3 Airworthiness, Documents & Currency
3.1 Required Pilot and Aircraft Documents 3.2 Inspections, Airworthiness Directives, and Preventive Maintenance 3.3 Inoperative Equipment and 91.213 3.4 Recent Flight Experience and the Flight Review
4 14 CFR Part 91 Operating Rules
4.1 Right-of-Way, Minimum Safe Altitudes, and Speed Limits 4.2 VFR Cruising Altitudes, Altimeter Settings, and Oxygen 4.3 Fuel Requirements, Transponder, ADS-B, and ELT 4.4 NOTAMs, TFRs, and Accident/Incident Duties
5 National Airspace System
5.1 Class A, B, and C Airspace 5.2 Class D, E, and G Airspace and VFR Weather Minimums 5.3 Special Use Airspace 5.4 Other Airspace, TFRs, TRSA, ADIZ, and SFRA
6 Aviation Weather Theory
6.1 Atmosphere, Pressure, Temperature, and Density 6.2 Stability, Clouds, and Moisture 6.3 Air Masses and Fronts 6.4 Wind, Jet Stream, and Local Wind Systems
7 Weather Hazards
7.1 Thunderstorms and Convective Weather 7.2 Structural Icing, Frost, and Carburetor Ice 7.3 Fog, Low Ceilings, and Visibility 7.4 Wind Shear, Microbursts, Turbulence, and Mountain Waves
8 Weather Products & Briefings
8.1 METAR Decoding 8.2 TAF and Graphical Forecast Products 8.3 PIREPs, AIRMET, SIGMET, Convective SIGMET, and Winds Aloft 8.4 Briefings and Go/No-Go Decisions
9 Principles of Flight
9.1 Four Forces and Lift Production 9.2 Angle of Attack, Critical AoA, and Stalls 9.3 Drag, L/D, and Ground Effect 9.4 Axes, Stability, and Flight Controls
10 Maneuvering Flight, Stalls & Spins
10.1 Load Factor, Bank Angle, and Stall Speed 10.2 Left-Turning Tendencies 10.3 Slow Flight, Power-On/Off Stalls, and Spin Awareness 10.4 Steep Turns and Ground-Reference Maneuvers
11 Powerplant, Fuel & Electrical Systems
11.1 Reciprocating Engines, Mixture, Detonation, and Preignition 11.2 Ignition, Magnetos, Carburetor vs Fuel Injection 11.3 Fuel Grades, Contamination, and Fuel-System Management 11.4 Electrical System and Alternator Failure
12 Flight Instruments & Avionics
12.1 Pitot-Static Instruments and Blockage Errors 12.2 Gyroscopic Instruments, Vacuum Failure, and Magnetic Compass Errors 12.3 Engine Instruments, Transponder Modes, and Basic Avionics
13 Aircraft Performance
13.1 Pressure Altitude, Density Altitude, and Performance Effects 13.2 Takeoff and Climb Performance 13.3 Cruise, Descent, and Landing Performance 13.4 Wind, Gradient, Surface, and Crosswind Component
14 Weight and Balance
14.1 Weight-and-Balance Principles 14.2 Moment, CG, and Sample Computations 14.3 Forward and Aft CG Effects 14.4 V-Speeds, Markings, and Limitation Placards
15 Charts, Pilotage & Dead Reckoning
15.1 Sectional Chart Symbology and Airspace Depiction 15.2 Pilotage and Dead Reckoning 15.3 Variation, Deviation, Wind Triangle, and E6B 15.4 VFR Cross-Country and Fuel Planning
16 Radio Navigation, Lost Procedures & Airport Operations
16.1 VOR Navigation 16.2 GPS, RAIM, and Radar Services 16.3 Lost Procedures and Diversion 16.4 Communications, Light-Gun Signals, Lighting, and Traffic Patterns
17 Aeromedical Factors
17.1 Hypoxia, Hyperventilation, and Carbon Monoxide 17.2 Spatial Disorientation, Illusions, and Vision 17.3 Scuba-to-Flight, Alcohol/Drugs, and IMSAFE
18 ADM, Night Operations & Emergencies
18.1 ADM, Hazardous Attitudes, PAVE, and DECIDE 18.2 Night Operations and Night Illusions 18.3 Emergency Descent, Engine Failure, and System Malfunctions 18.4 Survival Gear, ELT, and Forced-Landing Considerations
19 Preflight Procedures & Airport Ground Operations
19.1 Preflight Assessment, Airworthiness Determination, and the Preflight Inspection 19.2 Flight Deck Management, Passenger Briefings, and Engine Starting 19.3 Taxi Operations: Signs, Markings, Lighting, and Runway Incursion Avoidance 19.4 Before-Takeoff Check, After-Landing, and Securing the Airplane
20 Class-Specific Knowledge: Seaplane & Multiengine
20.1 Seaplane and Water Operations Knowledge 20.2 Multiengine Knowledge: VMC, VYSE, and Engine-Out Fundamentals
17.1 Hypoxia, Hyperventilation, and Carbon Monoxide
Key Takeaways Explain This Topic AI
PHAK Chapter 17 names four hypoxia types: hypoxic (altitude / low partial pressure), hypemic (CO, blood donation, smoking, anemia), stagnant (G-loads, cold, poor circulation), and histotoxic (alcohol, cyanide, some drugs).
Treat suspected hypoxia with supplemental oxygen and a descent; time of useful consciousness shrinks rapidly above 10,000 feet (PHAK) and AIM 8-1-2 gives 20–30 minutes at 18,000 feet and 5–12 minutes at 20,000 feet.
Hyperventilation blows off carbon dioxide and mimics hypoxia; the cure is slower normal breathing, talking or singing, or a paper bag — not oxygen alone at a low altitude.
Carbon monoxide from an exhaust or cabin-heater leak causes hypemic hypoxia; shut the heat off, open vents, use 100 percent oxygen if available, and land.
Ear and sinus blocks (ACS PA.I.H.K1c) happen most on descent when a cold or allergy plugs the Eustachian tube or sinus openings; do not launch congested, and use a gentle Valsalva rather than an oral decongestant that impairs you.
Last updated: August 2026
ACS PA.I.H.K1 asks for symptoms, recognition, causes, effects, and corrective actions. The written test will not give you a pulse-oximeter printout. It will give you a cause (altitude, a heater, a beer, a cold) and ask which problem you have and what you do first. PHAK Chapter 17 and AIM 8-1 are the source text.
Four hypoxia types — name the broken link
Hypoxia is not “not enough air in the sky.” The atmosphere is still about 21 percent oxygen from sea level to space (AIM 8-1-2). What changes with altitude is barometric pressure , so each breath delivers fewer oxygen molecules to the blood. Hypoxia means the tissues — especially the brain — are not getting enough oxygen to work. PHAK splits that failure into four places in the chain:
Type Broken link Classic PAR causes What still works
Hypoxic Not enough oxygen available to the lungs (low partial pressure) Unpressurized altitude; a failed or unused oxygen system Blood and cells are fine if you restore pressure or add O₂
Hypemic Blood cannot carry a normal oxygen load Carbon monoxide , smoking, blood donation , anemia, blood loss Cabin air may be 21 percent O₂; hemoglobin is occupied or missing
Stagnant Oxygen-rich blood is not circulating High-G maneuvers, cold vasoconstriction, heart problems, shock Lungs and hemoglobin are fine; flow is not
Histotoxic Cells cannot use the oxygen that arrives Alcohol , cyanide, some drugs / narcotics Delivery is fine; the mitochondria are poisoned
Memorize the names by the prefix. Hypo-oxic is a shortage at the lung. Hyp-emic is a blood ( hemo ) problem. Stagnant is stalled circulation. Histo-toxic is poisoned tissue. The exam’s favorite swap is calling a CO leak “hypoxic hypoxia” because the airplane is at 8,500 feet. The altitude may add hypoxic stress, but the CO is hypemic : hemoglobin prefers carbon monoxide on the order of 200 times more than oxygen, so the blood is carrying the wrong molecule.
PHAK’s alcohol note belongs here, not only in the 91.17 section: one ounce of alcohol can equate to about an additional 2,000 feet of physiological altitude . A hangover is still histotoxic hypoxia. Smoking is hypemic plus a night-vision penalty. A weekend blood donation is hypemic until the red-cell count recovers — PHAK tells pilots to stay on the ground for a period after donating; do not invent a published hour count the handbook does not give.
Symptoms and time of useful consciousness
The trap is that hypoxia feels like confidence. Early signs include euphoria or a carefree, belligerent mood, headache, delayed reaction, impaired judgment, visual trouble, drowsiness, lightheadedness, tingling in fingers and toes, numbness, and later cyanosis (blue fingernails and lips) and tunnel vision. AIM 8-1-2: night vision can degrade at a cabin altitude as low as 5,000 feet ; other significant effects in a healthy pilot usually wait until about 12,000 feet . From 12,000 to 15,000 feet , judgment, memory, alertness, coordination, and calculation go first. Performance can deteriorate seriously within 15 minutes at 15,000 feet . Above 15,000 feet the visual field grays from the outside in.
Time of useful consciousness (TUC) , also called effective performance time, is the interval between oxygen interruption (or arrival in an oxygen-poor cabin) and the moment you can no longer do something useful — don a mask, start a descent, talk to ATC. PHAK’s conceptual rule is that above 10,000 feet, TUC decreases rapidly . Do not memorize a third-party “TUC card” that is not in the book you are citing. AIM 8-1-2 publishes the numbers PAR items actually sample:
- Cabin / flight condition (AIM 8-1-2) What happens
- About 5,000 feet Night vision already declining
- Below ~12,000 feet (healthy, daytime) Other obvious hypoxia effects usually not yet
12,000–15,000 feet Judgment, memory, coordination, calculation degrade; headache, drowsiness, euphoria or belligerence
- 15,000 feet Performance can collapse within 15 minutes
- 18,000 feet Ability to take corrective action lost in 20 to 30 minutes
- 20,000 feet That window shrinks to 5 to 12 minutes , then unconsciousness
Those AIM times assume a relatively sudden exposure. Exertion, cold, heat, fever, anxiety, smoking, anemia, alcohol, and antihistamines all lower the altitude at which the same impairment appears. A smoker at 9,000 feet night VFR is not “below the hypoxia chapter.”
Treatment is oxygen and a descent — both, not a philosophical debate about which one is more elegant. Put on the mask or cannula, select oxygen, start down toward an altitude where room air works (think at or below 10,000 feet unless the airplane and 91.211 require more), and do not wait for cyanosis. Chamber training at CAMI or a military physiology unit is how you learn your personal symptom order; the written test still wants the generic list plus “oxygen and descend.”
Hyperventilation is a CO₂ problem, not an O₂ problem
Hyperventilation (PA.I.H.K1b) is breathing too fast or too deep so that you blow off carbon dioxide . Blood vessels in the brain constrict. Symptoms look insultingly like hypoxia: lightheadedness, visual change, tingling, hot-and-cold feelings, suffocation, drowsiness, muscle spasms, then incoordination and unconsciousness. AIM 8-1-3 adds that the frightened pilot often breathes even faster, which makes it worse.
The altitude and the story tell the two apart. Tingling and a racing breath after a scary radio call at 3,500 feet is hyperventilation. The same tingling at 13,500 feet after 40 minutes without oxygen is hypoxia until proven otherwise. They can also travel together.
Corrective action from PHAK and AIM:
Consciously slow the rate and depth of breathing back to normal. Symptoms usually fade in a few minutes.
Talk, sing, or count aloud so the airway cannot race.
Breathe into a paper bag (or a similar closed volume) to rebuild CO₂ if you have one.
If you are already on an oxygen system when the symptoms start, AIM 8-1-3 is specific: set the regulator to 100 percent oxygen , verify the system is actually delivering, then fix the breathing rate. That sequence exists because hypoxia and hyperventilation overlap and hypoxia will kill you first.
The PAR trap is “treat hyperventilation with oxygen only” at pattern altitude. Extra oxygen does not replace the CO₂ you exhaled. At 2,000 feet AGL the right first move is slow the breathing. At FL180 the right first move is 100 percent oxygen and a descent, then sort out the breathing.
Carbon monoxide — the heater you cannot smell
Carbon monoxide (PA.I.H.K1f) is colorless, odorless, and tasteless (AIM 8-1-4). Light-airplane cabin heat typically picks up air that has flowed over the exhaust muffler. A crack or leaking seal puts exhaust — and CO — into the heat muff. CO binds hemoglobin and produces hypemic hypoxia . Smokers already carry a CO load before they start the engine.
Symptoms: headache , drowsiness, dizziness, blurred vision, weakness. A cherry-red complexion or cherry-red lips is the classic late medical sign of severe CO poisoning; do not wait for it. An exhaust odor is a gift. Many trainers carry a chemical spot detector on the panel; treat a darkening spot as a leak until a mechanic says otherwise.
Immediate actions, in order you can actually fly:
Cabin heat off. You just closed the path from the muffler into the cockpit.
Vents and windows open to dilute what is already inside.
100 percent oxygen if the airplane has it — you are treating hypemic hypoxia by flooding whatever hemoglobin is still free.
Land at the nearest suitable airport. If symptoms stay after shutdown, get medical care. AIM 8-1-4 is explicit about shutting the heater, opening vents, and seeing a physician when symptoms are severe or persist.
Do not “turn the heat up to stay warm” and do not diagnose a winter headache as “just dehydration” while the muffler is leaking.
Ear and sinus blocks — PA.I.H.K1c
The middle ear is a closed box behind the eardrum. The Eustachian tube vents it to the throat. On climb , expanding middle-ear air usually pops the tube open by itself. On descent , outside pressure rises and you must open the tube on purpose: swallow, yawn, chew, tense the throat, or a gentle Valsalva (mouth closed, pinch the nose, blow softly). A cold, allergy, or sore throat swells the tube shut. The eardrum is then driven inward, with pain, hearing loss, and a risk of rupture or an infected fluid collection.
Sinus block is the same physics in the frontal (above the eyebrow) or maxillary (cheek / upper-teeth) sinuses. It is most common on descent . Pain can be stunning. Bloody mucus is a clue the lining tore.
Prevention is not a stronger spray. AIM 8-1-2: do not fly with an upper-respiratory infection or nasal allergy. Decongestant sprays rarely protect the tube for a whole flight, and oral decongestants have side effects that impair a pilot . If a block has not cleared shortly after landing, see a physician. The private-pilot answer is to stay on the ground with the cold — that is also an IMSAFE and 61.53 decision, developed in 17.3.
Scenario: Maya, 9,500 feet, and the “just a headache” heater
Maya is cruising a 172 at 9,500 feet on a January cross-country. Cabin heat is full. She feels a dull headache and a little sleepy, then notices her passenger’s lips look oddly flushed. She tells herself it is hypoxia from altitude and reaches only for the oxygen cannula her instructor left in the back.
Oxygen helps a little. It does not fix a leaking muffler. Maya is looking at hypemic hypoxia from CO , maybe stacked on a little hypoxic stress. Heat off , vents open , oxygen if she has it, and a landing — not a continued cruise with the heater “just a bit lower.” If the same headache had started after a go-around at 1,200 feet with no heat and a panicked radio call, she would slow her breathing and talk, not climb for “more air.” Cause first, then the matching fix.