Document
OAS-43A (12/12)
Interagency Aviation
Accident Prevention Bulletin
No. IA APB 22-04 Date: July 14, 2022 Page 1 of 2 Subject: Hypoxia in an Unpressurized Aircraft Area of Concern: Flight Safety Distribution: All Aviation Activities Discussion: One of the most perilous emergencies an aircrew can face is pilot incapacitation and, it can happen so slowly that the pilot and crew may not even realize it. Hypoxia is a condition where oxygen is not available in sufficient amounts resulting in inadequate oxygen delivery to the brain and tissues of the body. All are susceptible to hypoxia at high altitudes in unpressurized aircraft. Hypoxia can impair the functions of the brain and organs and can lead to grave consequences.
A recent SAFECOM ( #22-0356 ) described a situation where a helicopter pilot began to experience the onset of hypoxia while performing an aerial supervision mission. Fortunately the pilot was able to recognize the symptoms, descend to a lower altitude and safely land the aircraft.
What causes Hypoxia? As the altitude increases, the air pressure
Symptoms of Hypoxia
decreases, reducing the concentration of oxygen reaching the bloodstream. In other words, with increasing altitude, the partial • Euphoria pressure of oxygen gets lower and the lungs cannot effectively • Headache transfer oxygen from the air to the blood to be carried to all tissues • Increased response time in the body. Hypoxia has a variety of symptoms and each person • Impaired judgment may be affected or react differently. Other factors such as rate of • Drowsiness ascent, time spent at altitude, fatigue, self-imposed stresses, and individual physiological fitness can all affect the onset of hypoxia.
• Dizziness Exposure to carbon monoxide while operating near a fire could also • Tingling in fingers and toes reduce the altitude and onset of hypoxia.
• Numbness Preventing Hypoxia . The FAA has already developed • Blue fingernails and lips supplemental oxygen policies to prevent the onset of hypoxia and (cyanosis) understanding and following these is important. While pilots • Limp muscles receive training on altitude and hypoxia prevention, a recent study • Confusion or foggy decision- showed that nearly 50% of the pilots responding had never making experienced the effects of hypoxia. Outside of hyperbaric chamber training, many pilots don’t have the experience to draw from to remind them of the warning signs of hypoxia.
No. IAAPB 22-04 July 14, 2022 Page 2 of 2 FAA REQUIREMENTS In Part 135 Commuter and On Demand operations in unpressurized aircraft, the required minimum flight crew must use supplemental oxygen for that part of the flight that exceeds 30 minutes above 10,000 feet through 12,000 feet MSL. Above 12,000 feet MSL each member of the flight crew must use supplemental oxygen during the entire portion of the flight at those altitudes (14 CFR § 135.89, § 135.157, § 121.327, & § 121.329).
In Part 91 General Aviation operations the required flight crew must use supplemental oxygen for any portion of the flight that exceeds 30 minutes above a cabin pressure altitude of 12,500 feet mean sea level (MSL) up to and including 14,000 feet (MSL). The flight crew must use supplemental oxygen for the entire duration of flight operations above a cabin pressure altitude of 14,000 feet MSL (14 CFR § 91.211).
Don’t be confused by the term public aircraft operation. The FAA guidelines still apply. These rules are set up as guidelines to prevent hypoxia and the type of operation doesn’t change human physiology. A contractor must abide by the contract and FAA requirements. Fleet pilots operate under Part 91.
SAFECOM 22-0356 provides an important lesson on the effects of hypoxia. The FAA has temporarily discontinued the Physiology Training due to COVID-19 restrictions. But when it resumes, it is a great opportunity to understand and experience the effects of hypoxia.
If mission planning identifies the need for high altitude operations, first ensure that you have the right aircraft for the mission and then ensure supplemental oxygen is readily available. Additional information for o perating at altitude with unpressurized aircraft and the requirements for supplemental oxygen is available from the FAA.
The insidious nature of hypoxia requires you to be constantly aware of how you and your crew feel. Once hypoxia is recognized, quick and decisive action means recovery is only seconds away.
/s/ John Mills /s/ Lori Clark John Mills Lori Clark Acting Chief, Aviation Safety, Program Branch Chief - Aviation Safety Management Evaluation, and Quality Management Systems DOI, Office of Aviation Services USDA, Forest Service