Task VIII.A
Supplemental Oxygen
To determine the applicant exhibits satisfactory knowledge, risk management, and skills associated with flight at higher altitudes where supplemental oxygen is required or recommended.
References: 14 CFR part 91; AC 61-107; AIM; FAA-H-8083-2, FAA-H-8083-3, FAA-H-8083-25; POH/AFM
Quick Review
Conversational Q&A — quiz yourself before the oral.
You met 91.211 as a private pilot. At the commercial level the examiner expects you to work the numbers cold, pick the right oxygen system for the altitude, compute a duration in a scenario, and brief passengers on the mask — all of it in a professional-pilot context where the airplane may actually go there.
Three thresholds, all cabin pressure altitude:
- Above 12,500 ft up to and including 14,000 ft — the required minimum flight crew must be provided with and use oxygen for that portion of flight of more than 30 minutes duration
- Above 14,000 ft — the required minimum flight crew uses oxygen for the entire flight time at those altitudes
- Above 15,000 ft — each occupant must be provided oxygen (91.211)
Note the asymmetry the examiner is fishing for: crew must use it; passengers must only be provided it.
- Above FL250 — at least a 10-minute supply of supplemental oxygen, in addition to the 91.211(a) oxygen, must be available for each occupant for a descent forced by loss of pressurization
- Above FL350 — one pilot at the controls must be wearing and using a mask that is secured and sealed and either supplies oxygen at all times or automatically supplies it whenever cabin altitude exceeds 14,000 ft
- Exception at or below FL410 — the mask need not be worn if there are two pilots at the controls and each has a quick-donning mask placeable with one hand within 5 seconds (91.211(b))
If either pilot leaves the controls above FL350, the remaining pilot puts the mask on until the other returns (91.211(b)(2)).
- Hypoxic — insufficient oxygen available to the body as a whole; at altitude it's the drop in partial pressure of oxygen, not the percentage (the atmosphere stays about 21 percent oxygen from the surface out to space — AIM 8-1-2)
- Hypemic — the blood can't take up or transport oxygen; most common form is CO poisoning, also anemia, blood loss, recent blood donation
- Stagnant — oxygen-rich blood isn't moving; G-loading, shock, cold-restricted circulation
- Histotoxic — the cells can't use the oxygen delivered; alcohol, narcotics, poisons (PHAK ch. 17)
One ounce of alcohol equates to roughly an additional 2,000 ft of physiological altitude (PHAK ch. 17).
Symptoms:
- Cyanosis (blue fingernails and lips)
- Headache
- Increased reaction time and decreased response to stimuli
- Impaired judgment
- Euphoria
- Visual impairment
- Drowsiness, dizziness, tingling in the fingers and toes, numbness
As it worsens the visual field narrows and instrument interpretation gets hard (PHAK ch. 17).
Why dangerous: euphoria and impaired judgment give you a false sense of security while your performance is already degraded, so you don't self-diagnose. That's why the fix is regulatory and mechanical — put the mask on at the altitude, don't wait to feel bad.
TUC (also called effective performance time) is the time from interruption of the oxygen supply to the point where you can no longer take proper corrective and protective action (AC 61-107B para 2-7). It is not the onset of unconsciousness — impairment can be immediate.
From AC 61-107B Figure 2-3, sitting quietly:
| Altitude | TUC/EPT | Following rapid decompression |
|---|---|---|
| 18,000 ft | 20–30 min | 10–15 min |
| 22,000 ft | 10 min | 5–6 min |
| 25,000 ft | 3–5 min | 1.5–2.5 min |
| 28,000 ft | 2.5–3 min | 1–1.5 min |
| 30,000 ft | 1–2 min | 30 s–1 min |
| 35,000 ft | 30 s–1 min | 15–30 s |
| 40,000 ft | 15–20 s | nominal |
| 43,000 ft and above | 9–12 s | nominal |
- Rate of decompression — rapid decompression cuts TUC by at least 50 percent (para 2-7(b)); for the specific band between 25,000 ft and 43,000 ft, assume the reduction is 50 percent (para 2-7(a))
- Rate of ascent — the faster you get there, the shorter it is
- Physical activity — ten deep knee bends at 25,000 ft with the mask off cuts TUC by 50 percent
- Fatigue, low blood glucose, alcohol, medications, smoking, poor conditioning, illness (AC 61-107B para 2-7)
Published TUCs are averages with wide individual variation, so assume the lower value is limiting (AC 61-107B).
- Continuous flow — supplies oxygen at a set or automatic rate; the mask has a rebreather bag that collects oxygen during exhalation so the next inhalation is less diluted. Usually the passenger system. Certificated up to 41,000 ft, but capability requires very careful attention above 25,000 ft (AC 61-107B para 2-9)
- Diluter demand — delivers only on inhalation; an automix lever blends cabin air and oxygen by altitude or gives 100 percent. Tight-sealing mask, safe to 40,000 ft
- Pressure demand — same as diluter demand plus positive pressure to the facepiece so the lungs are pressurized; this is what makes it safe above 40,000 ft (PHAK ch. 7, AC 61-107B)
Demand systems waste no oxygen between breaths, which is why they're on the crew side.
Aviator's gaseous oxygen is Grade A, Type I, minimum purity 99.5 percent by volume excluding moisture, with no more than 0.005 mg of water vapor per liter at 760 mm Hg and 68 °F. It must be odorless and free of contaminants including drying agents (FAA Introduction to Aviation Physiology, CAMI, ch. 8). Current guidance specifies oxygen meeting or exceeding SAE AS8010, Aviator's Breathing Oxygen Purity Standard (PHAK ch. 7, AC 61-107B para 2-9).
The controlling difference is moisture. Medical and industrial ("technical") oxygen carry water vapor that can freeze in the lines and regulator at altitude and block the flow, and industrial grades may carry impurities. Do not confuse the three.
- Materials that are nearly fireproof in ordinary air burn readily in oxygen; oils and greases can ignite on contact and must never be used on oxygen valves or fittings
- Smoking is prohibited during any use of oxygen equipment; verify all flow is shut off after use
- Service only outside the hangar, with hands, clothing, and tools free of oil, grease, lip salve, and hair oil
- Portable bottles must be secured against displacement in turbulence
- Bottles get hydrostatic testing at a DOT-approved facility; the system is inspected by a certificated maintenance provider (AC 61-107B para 2-9, PHAK ch. 7)
Not necessarily. Pressure varies directly with temperature at constant volume, so an oxygen cylinder cold-soaked in an unheated compartment shows a lower indicated pressure without any loss of oxygen. Aircraft oxygen is normally stored at 1,800–2,200 psi in high-pressure systems, and containers are marked with the psi tolerance before filling (PHAK ch. 7, AC 61-107B para 2-9).
Rule it out by comparing against temperature before you assume a leak — but if the drop is progressive in flight, treat it as a leak and plan a descent.
With clean hands:
- Mask and tubing for tears, cracks, or deterioration
- Regulator valve and lever condition and position
- Quantity and pressure gauge indication
- Location and function of pressure gauges, flow indicators, and connections
- Don the mask and test the system — including mask-microphone communication with ATC on installed crew systems (AC 61-107B para 2-9, AFH ch. 15)
If you're flying a cannula system, the green flow detector belongs in your regular scan. Cannulas aren't approved in place of masks on aircraft with oxygen systems certified for operations above 18,000 ft (PHAK ch. 7).
Deep Dive
Working an oxygen quantity problem
The skill element is explicit: determine the quantity of supplemental oxygen required in a scenario given by the evaluator (CA.VIII.A.S1). The examiner wants a repeatable method, not a memorized number — you compute from the POH/AFM duration chart, then add margin.
An electrical pulse-demand system senses the inhalation effort and delivers oxygen only during the initial portion of the breath, so nothing is dumped into the cabin during exhalation. Compared with continuous flow, it can cut oxygen consumption by 50–85 percent. Most also carry an internal barometer that automatically increases the delivered pulse as altitude increases (PHAK ch. 7).
For a commercial operator flying a long unpressurized leg in the mid-teens, that is the difference between one bottle and three.
Risk management at altitude
- Physiological — hypoxia with a shrinking TUC, hyperventilation, gas expansion in the ears and GI tract, and decompression sickness — altitude DCS is a potential risk every time you fly an unpressurized aircraft above 18,000 ft (AC 61-107B para 2-7, PHAK ch. 17)
- Equipment — mask fit and seal, a beard or mustache breaking the seal on a demand mask, hose purge time, cannula limits above 18,000 ft
- Weather and airspace — jet stream winds, clear air turbulence, Class A entry at 18,000 ft requiring an IFR clearance
- Compressed gas — a bottle at 1,800–2,200 psi becomes a projectile in an explosive decompression if it isn't strapped down (AC 61-107B para 2-11)
- Fire — an oxygen-rich cabin makes ordinary materials combustible; grease on a fitting is an ignition source
You often can't tell in the moment: visual impairment, dizziness, tingling, and lightheadedness show up on both lists. You don't have to. The recovery is the same for either — breathe 100 percent oxygen and slow the breathing rate down (AC 61-107B para 2-11). Oxygen will not worsen hyperventilation.
One thing to expect: recovering from a deep hypoxia exposure on 100 percent oxygen can make symptoms appear to worsen for 15–60 seconds. Push through it; the procedure doesn't change. If symptoms persist, descend and land as soon as possible.
Initiate an emergency descent to below 10,000 ft MSL and land as soon as possible if symptoms persist (AC 61-107B para 2-11). Advise ATC — the descent is your priority but they need to clear the airspace beneath you. The maneuver itself is Task IX.A; here the examiner wants to see you connect the physiological trigger to the decision without hesitating.
Piston caution: a high-altitude rapid descent can cold-shock the cylinders. That's a real consideration on a planned descent — it is not a reason to delay one you need for hypoxia.
Passenger briefing
Cover it on the ground, before the mask matters:
- Where the mask or cannula is stowed and how to reach it seated and belted
- How to don it — over the head, seal on the face, and for a continuous-flow mask, that the reservoir bag will not always inflate visibly and that's normal
- How to verify flow — the green flow indicator on a cannula, bag movement on a mask
- No smoking at any time the system is in use
- When you'll call for masks, and that they should don theirs before helping anyone else
- Don't touch the regulator or bottle valve; call you
For a pressurized airplane, add what a decompression looks and sounds like — fog, noise, cold — so nobody freezes when it happens (CA.VIII.A.S3; AC 61-107B para 2-11).
The single-pilot problem at altitude is that your judgment is the first thing hypoxia takes, so you build the defenses before you need them:
- Preflight — oxygen quantity, duration chart, mask fit, and a personal altitude limit set on the ground
- In flight — a pulse oximeter in the scan gives an objective number when your self-assessment is unreliable (PHAK ch. 7); set a hard SpO₂ floor at which you descend
- Automation — let the autopilot fly while you don the mask; hand-flying while hypoxic is the wrong workload split
- ATC — tell them early. "Unable to maintain, descending" buys you the block you need
- Passengers — a briefed passenger who can hand you a mask is a resource (CA.VIII.A.S4)
Official ACS elementsreference
Knowledge9 elements
The applicant demonstrates understanding of:
CA.VIII.A.K1Regulatory requirements for supplemental oxygen use by flight crew and passengers.CA.VIII.A.K2Physiological factors, including:CA.VIII.A.K2aImpairmentCA.VIII.A.K2bSymptoms of hypoxiaCA.VIII.A.K2cTime of useful consciousness (TUC)CA.VIII.A.K3Operational factors, including:CA.VIII.A.K3aCharacteristics, limitations, and applicability of continuous flow, demand, and pressure-demand oxygen systemsCA.VIII.A.K3bDifferences between and identification of “aviator’s breathing oxygen” and other types of oxygenCA.VIII.A.K3cPrecautions when using supplemental oxygen systems
Risk Management4 elements
The applicant is able to identify, assess, and mitigate risk associated with:
CA.VIII.A.R1High altitude flight.CA.VIII.A.R2Use of supplemental oxygen.CA.VIII.A.R3Management of compressed gas containers.CA.VIII.A.R4Combustion hazards in an oxygen-rich environment.
Skills4 elements
The applicant exhibits the skill to:
CA.VIII.A.S1Determine the quantity of supplemental oxygen required in a scenario given by the evaluator.CA.VIII.A.S2Operate or simulate operation of the installed or portable oxygen equipment in the airplane, if installed or available.CA.VIII.A.S3Brief passengers on use of supplemental oxygen equipment in a scenario given by the evaluator.CA.VIII.A.S4Use single-pilot resource management (SRM) or crew resource management (CRM), as appropriate.