AME Aerospace Physiology & Human Factors 1 — Questions and Answers
Question 1: At what altitude does the FAA require supplemental oxygen for flight crew members when flying in an unpressurized cabin above 12,500 feet MSL for more than 30 minutes?
- Above 10,000 feet MSL at all times
- Above 12,500 feet MSL for more than 30 minutes; above 14,000 MSL at all times (Correct answer)
- Above 14,000 feet MSL for more than 30 minutes only
- Above 15,000 feet MSL at all times
Correct answer: Above 12,500 feet MSL for more than 30 minutes; above 14,000 MSL at all times
14 CFR 91.211 requires supplemental oxygen for required flight crew above 12,500 feet MSL if flight exceeds 30 minutes, and at all times above 14,000 feet MSL.
14 CFR 91.211 establishes: (1) above 12,500 to 14,000 feet MSL: supplemental O2 required if flight exceeds 30 minutes; (2) above 14,000 feet MSL: supplemental O2 required for required flight crew at all times; (3) above 15,000 feet MSL: O2 must be provided to all occupants. This is relevant to AMEs because hypoxia is a major physiological hazard, and AMEs must understand these regulations to counsel airmen and evaluate hypoxia-related incidents.
Question 2: What is the 'time of useful consciousness' (TUC) at 35,000 feet following rapid decompression, and what is its significance for aviation medical examiners?
- 30-60 seconds; AMEs must ensure pilots understand the urgency of immediate emergency descent
- 5-10 minutes; pilots have adequate time for controlled descent at this altitude
- 15-20 seconds; AMEs must counsel on the critical importance of immediate oxygen mask donning (Correct answer)
- 2-3 minutes; standard emergency procedures provide adequate time
Correct answer: 15-20 seconds; AMEs must counsel on the critical importance of immediate oxygen mask donning
TUC at 35,000 feet following decompression is approximately 15-20 seconds - an extremely short window emphasizing the critical need for immediate oxygen mask donning before incapacitation occurs.
Time of useful consciousness decreases dramatically with altitude: at 25,000 ft it is approximately 3-5 minutes, at 30,000 ft about 1-2 minutes, and at 35,000 ft approximately 15-20 seconds following rapid decompression. The significance for AMEs includes counseling on the physiological urgency of oxygen mask donning drills and understanding that even mild pre-existing conditions affecting cerebral oxygenation could further reduce TUC. Hypoxic incapacitation can be insidious - euphoria and impaired judgment often precede complete incapacitation.
Question 3: What is the primary concern regarding the use of antihistamines by a certificated pilot, and how should the AME counsel on this?
- Antihistamines cause cardiac arrhythmias and are absolutely prohibited at all times
- First-generation antihistamines cause significant sedation and are not approved for use while flying; second-generation non-sedating antihistamines may be acceptable after an adequate observation period (Correct answer)
- All antihistamines are approved for pilot use as long as symptoms are controlled
- Antihistamines are only prohibited for ATP certificate holders
Correct answer: First-generation antihistamines cause significant sedation and are not approved for use while flying; second-generation non-sedating antihistamines may be acceptable after an adequate observation period
First-generation antihistamines such as diphenhydramine are sedating and not approved for use while flying; second-generation antihistamines may be acceptable for some pilots with an appropriate wait time after dosing.
First-generation antihistamines including diphenhydramine, chlorpheniramine, and hydroxyzine cause significant CNS sedation, impair psychomotor function, and reduce reaction time. They are definitively prohibited for use while exercising airman privileges. Second-generation antihistamines such as loratadine, cetirizine, and fexofenadine have reduced CNS penetration. Fexofenadine is generally preferred as it has the least sedating profile. FAA guidance requires a minimum observation period after initiating any antihistamine before flying - generally at least 48 hours to assess individual response.
Question 4: What is decompression sickness (DCS), and at what altitude does it become a significant risk for non-pressurized flight operations?
- Oxygen toxicity occurring above 20,000 feet
- The formation of nitrogen bubbles in tissues due to rapid pressure reduction, significant above 18,000 feet MSL (Correct answer)
- Carbon monoxide poisoning from engine exhaust, significant above 10,000 feet
- Inner ear barotrauma from rapid ascent, significant above 25,000 feet
Correct answer: The formation of nitrogen bubbles in tissues due to rapid pressure reduction, significant above 18,000 feet MSL
DCS results from dissolved nitrogen forming bubbles in tissues and blood when ambient pressure drops rapidly. It becomes a significant risk above approximately 18,000 feet MSL for unacclimatized individuals in non-pressurized aircraft.
Decompression sickness in aviation occurs when rapid ascent to high altitude reduces ambient pressure, causing dissolved nitrogen to come out of solution and form bubbles in tissues. Symptoms include joint pain, neurological symptoms, skin manifestations, and pulmonary symptoms. Significant DCS risk begins above approximately 18,000 feet MSL. Pilots who have been SCUBA diving are at elevated risk and should observe a surface interval (typically 12-24 hours depending on dive profile) before flying to high altitude.
Question 5: What physiological phenomenon is primarily responsible for spatial disorientation in IMC flight, and why is it relevant to the AME's evaluation of vestibular disorders?
- Hypoxia-induced cortical suppression
- The somatogravic illusion caused by linear acceleration during IMC
- The leans - a vestibular illusion from the semicircular canal limitations and false sensory inputs during sustained turns (Correct answer)
- Vertigo from Eustachian tube dysfunction during altitude changes
Correct answer: The leans - a vestibular illusion from the semicircular canal limitations and false sensory inputs during sustained turns
The leans and other vestibular illusions arise because the semicircular canals cannot detect slow rolls below their threshold, leading to false spatial orientation perceptions - directly relevant to AME evaluation of vestibular disorders.
The vestibular system's semicircular canals detect angular acceleration but only above a threshold rate of approximately 2-3 degrees per second. In IMC, a pilot entering a gradual bank below this threshold will not perceive the bank. If the aircraft then levels, the canals detect the roll back to level as a roll in the opposite direction, leading the pilot to believe they are banked when level - the leans. AMEs evaluating vestibular disorders must understand this mechanism because conditions affecting semicircular canal function impair the pilot's primary instrument for spatial orientation in IMC.
Question 6: Why is carbon monoxide (CO) poisoning a significant aviation medical concern, and what is the physiological basis for its impairment of oxygen delivery?
- CO reduces atmospheric oxygen concentration in the cockpit through combustion
- CO has 200-250 times greater affinity for hemoglobin than oxygen, forming carboxyhemoglobin that cannot carry oxygen and impairs oxygen offloading to tissues (Correct answer)
- CO directly inhibits mitochondrial cytochrome oxidase causing cellular hypoxia without reduced hemoglobin oxygen saturation
- CO causes bronchoconstriction that reduces alveolar oxygen exchange
Correct answer: CO has 200-250 times greater affinity for hemoglobin than oxygen, forming carboxyhemoglobin that cannot carry oxygen and impairs oxygen offloading to tissues
CO's clinical danger in aviation comes from its approximately 250x greater hemoglobin affinity compared to O2, forming stable carboxyhemoglobin that reduces effective oxygen-carrying capacity and impairs oxygen offloading to tissues.
Carbon monoxide binds to hemoglobin with approximately 200-250 times greater affinity than oxygen, forming carboxyhemoglobin (COHb). COHb molecules cannot carry oxygen, and CO binding also increases the oxygen affinity of remaining hemes causing a left shift of the O2-hemoglobin dissociation curve that impairs oxygen offloading to tissues. Standard pulse oximetry cannot distinguish COHb from oxyhemoglobin, meaning SpO2 readings appear normal while actual oxygen delivery is critically impaired. CO poisoning from heater exhaust leaking into the cabin is a significant aviation accident cause.
AME Aerospace Physiology & Human Factors 1
At what altitude does the FAA require supplemental oxygen for flight crew members when flying in an unpressurized cabin above 12,500 feet MSL for more than 30 minutes?