Why height challenges the body
The higher the altitude, the lower the ambient pressure; although the oxygen content of the air remains at around 21 per cent, less oxygen is available per breath. At around 18,000 ft, the air pressure is only about half that at sea level - the usable amount of oxygen per litre of air breathed is halved accordingly. The brain and eyes react particularly sensitively: concentration, decision-making ability and twilight vision diminish. The body can compensate for this in the short term (e.g. by breathing faster), but as altitude and flight duration increase, these mechanisms reach their limits.
When is oxygen mandatory?
The following applies to non-commercial flights in Europe (EASA Part-NCO):
- If the cabin or pressure head between 10 000 ft and 13 000 ft lies, must Flight-critical crew members utilise additional oxygen, as soon as the duration in this altitude band more than 30 minutes amounts to.
- From 13 000 ft must all on board Use additional oxygen - from the first minute.
Oxygen can also be useful below these limits, for example during night flights. Dark-sighted vision consumes a disproportionate amount of oxygen; many pilots report that an „oxygen shower“ can be as little as 6 000-8 000 ft noticeably improved recognition of lights and obstacles.
Recognising hypoxia - deceptively insidious
Hypoxia rarely announces itself with shortness of breath, but creeps in. Typical warning signs are diminishing visual acuity (especially at dusk), headaches, dizziness, tingling fingers/toes, slurred speech, tiredness or even euphoria. It is dangerous that one's own self-assessment suffers - those who have hypoxia often no longer realise that they are affected. Therefore: Objective measurement, not fly „by feel“.
How much time is left? - Time of Useful Consciousness (TUC)
If there is an abrupt lack of oxygen at high altitude (e.g. supply failure), there is only a limited window of time in which meaningful action is still possible:
- 18 000 ft: coarse 20-30 minutes (much less useful in the case of gradual hypoxia).
- 25 000 ft: only 3-5 minutes.
These values are Average values and fluctuate greatly - fitness, fatigue, temperature, smoking or previous stays at high altitude can noticeably change the TUC. Modern avionics in some touring aircraft monitor inactivity, issue acoustic warnings and can automatically descend into denser air; however, this should not be relied upon.
Equipment at a glance - what suits which application profile?
1) Nasal cannulae (standard and reservoir/preservation cannulae)
For up to 18 000 ft cannulas are permissible and very convenient, especially so-called Oxymiser/Oximyzer-variants with a small reservoir („moustache“ or pendant). These store the continuous flow during exhalation and deliver an oxygen „bolus“ at the start of inhalation - this increases efficiency and minimises the risk of injury. Saves bottle contents. Disadvantage: The effectiveness decreases with heavy mouth breathing. From 18 000 ft is a Mask prescribed.
2) Masks (oral-nasal, rebreather, sealing masks)
Masks cover the mouth and nose, function independently of mouth breathing and are mandatory above 18,000 ft. They dry out the mucous membranes more, interfere with speech and are less comfortable - but in terms of safety, they are still the most robust solution at higher altitudes.
3) On-demand/pulse-demand systems
Electronic controllers (e.g. Mountain High O2D2) give oxygen only when inhaling in precisely dosed pulses. Advantages: Significantly lower consumption, less dehydration, often two-place operation and warnings in the event of flow errors or apnoea. For frequent travellers, Alpine crossings or long legs, these systems are a best-in-class solution because they extend the cylinder duration many times over.
4) Portable bottle sets
From a simple single-seat kit to a multi-seat system, there are configured kits with lightweight cylinders (aluminium/carbon fibre), flowmeters, cannulas/masks and bag. For occasional flights over 8,000 ft or night flights, the Price/benefit ratio very good. Attention: Connection standards for filling/fittings differ between USA and Europe - plan for adapters.
5) Oxygen concentrators
Modern systems (e.g. Aithre Turbo) extract oxygen from the cabin air. They typically supply > 93 % O₂ until about 15-18 000 ft (depending on the number of people/power) and require on-board power. Useful for frequent users who unlimited stock recommended remains one bottle as a backup for higher load or failure.
Monitoring: measuring saturation instead of guessing
Since hypoxia progresses gradually, a Pulse oximeter in every cockpit. Standard values:
- Normal: about 95-98 % SpO₂ (individually slightly different).
- Need for action: < 90 % - Increase oxygen flow, decrease, check causes.
Many pilot watches/sports watches can now display SpO₂ and sound an alarm when values are low. Measurement errors are possible (cold fingers, nail varnish, strong vibrations) - therefore, if possible multiple times measure and watch for symptoms.
Practice: How to use oxygen correctly
Pre-flight
- Plan altitude profile and leg duration: Where do I exceed 10,000/13,000 ft? How long?
- Check equipment: Cylinder pressure, tightness, hoses/cannulas, mask seals, batteries for on-demand regulators.
- Allocation of roles: Who monitors SpO₂, who operates controllers? How do we react to symptoms?
In flight
- Start early: At night, tiredness or high workload earlier Utilise oxygen.
- Dose the flow: As little as necessary, as much as effective - SpO₂ and well-being guide the setting.
- Drink! Dry cabin air and oxygen dehydration.
- Hygiene: Fat free in the facial area; oxygen and oil/fat are a risky combination.
Emergency/escalation
- Symptoms → Increase oxygen flow, mask instead of cannula, immediately sink.
- System failure → Backup (second controller/reserve bottle/concentrator mode) or Emergency descent at a safe density level.
Refilling, storage, safety
- Medical vs. aviation O₂: In practice, high-purity oxygen is used for aviation; the decisive factors are Cleanliness and water/oil-free Fittings.
- Filling level Note in the logbook, observe cylinder hydrotesting/test deadlines.
- Transport Please note: Oxygen is a hazardous material; secure cylinders in the vehicle, fit valve protection, no heat zones.
- Adapters/Standards: Different threads/connections apply in Europe (DIN) and the USA (CGA) - incorrect adapters prevent leaks or damage.
Typical application scenarios
Night VFR at 6 000-8 000 ft: Cannula/reservoir cannula, low flow - visibility and attention benefit significantly.
Alpine crossing FL120-FL140: On-demand regulator with mask/cannula, SpO₂ monitoring, clear SOP for emergency descent.
Travelling with family in UL/SEP: Two- or multi-station portable set, simple operation, oximeter for all stations, water on board.
Regular high-altitude trips: Fixed installation or powerful on-demand regulator, concentrator plus bottle backup if necessary.
Brief summary
Additional oxygen is available above 10 000 ft not just a question of comfort, but a Safety factor - and from 13 000 ft mandatory for everyone on board. If you plan systematically, measure your own saturation and use the right equipment, you will stay safe even at high altitudes fit for flight. A trio has proven itself for many GA profiles: Pulse oximeter, Reservoir cannula or mask and a On-demand controller with sufficient bottle capacity - supplemented by clear SOPs for night, mountain and long legs.
Source references:
Aviation magazine
