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88 votes
Accepted

How do people suffering from hypoxia not realize they aren't getting enough oxygen?

The key point here is that your body does not measure blood oxygen levels. Instead, the urge to breathe is caused by a surplus of carbon dioxide in your blood. At sea level, this is fine: the only way ...
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48 votes

How could the Helios 522 passengers have survived so long without oxygen?

To add to Daniele's answer, from the final report: The forensic report concluded that the aircraft occupants had heart function during the impact. The report noted that this ...
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42 votes

Does breathing 100% oxygen cause health issues?

When we discuss a mixture of gasses, it's often useful to compute the pressure of each component separately. This is called the "partial pressure" of that component. For instance, oxygen ...
38 votes
Accepted

How could the Helios 522 passengers have survived so long without oxygen?

Consciousness requires quite a bit more oxygen than merely being alive. Human beings can last remarkably long with very little oxygen, but not remain conscious. And lack of oxygen will soon enough ...
31 votes
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Am I allowed to tell ATC "unable" if asked to climb to less than 12,500 ft without supplemental oxygen aboard?

FAR 91.211 only requires supplemental oxygen be used by the pilot/minimum required flight crew for that part of the flight at altitudes above 12,500 MSL to 14,000 MSL that is of more than 30 minutes ...
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27 votes

How do people suffering from hypoxia not realize they aren't getting enough oxygen?

No, lack of oxygen, in an of itself does not trigger negative physiological responses; quite the opposite. Most people who are affected by hypoxia have a general feeling of elation or euphoria and ...
22 votes
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Is flying at 14,000 MSL safe for children without supplemental oxygen?

Let me start out by saying that Aviation Stack Exchange is not a substitute for medical advice. Most of us aren't doctors (though I have medical training I am certainly not a doctor), and even if we ...
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16 votes
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Does oxygen become less available during night-time?

Night vision is one of the first things affected by reduced oxygen levels, and that effect is masked in daylight, but can become consequential at night. But no, the O2 molecules are the same night or ...
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16 votes

Does breathing 100% oxygen cause health issues?

Yes... but not predictably, and (almost certainly) not seriously. If you're worried for yourself and you're not already dead and not doing any crazy maneuvers, it is vanishingly unlikely that you need ...
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13 votes
Accepted

What was the first commercial aircraft to have a 'built-in' oxygen system?

The B307 may have been the first pressurized airliner, but it was usually flown at 12,000', and did not have a passenger supplemental oxygen system. Boeing 307 / C-75 Stratoliner 1938 "Captain ...
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13 votes

Do modern airliners have oxygen sensors in the cabin?

While it would not significantly affect the O₂ percentage one thing that must be tabulated on a cargo aircraft is the amount of dry ice loaded. Dry ice is very common in packaging to keep perishable ...
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13 votes

How could the Helios 522 passengers have survived so long without oxygen?

Here is a list of those people who survived as stowaway in the unpressurized and extremely cold wheel well. On June 19, 2015 an unidentified male who was 24 years old survived 11(!!) hours in the ...
12 votes

How do people suffering from hypoxia not realize they aren't getting enough oxygen?

As someone who has experienced hypoxia numerous times, the simple answer is that as you climb at 500-1000fpm into thinner air, the effects are very subtle, and, having compared them with other people, ...
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10 votes

What are the advantages of Chemical Oxygen Generation over Gaseous Canisters on board of aircrafts?

Pressurized oxygen tanks have two big minus points: they are heavy, and they are essentially a small bomb. But they have two big plus points: they can be refilled easily and they don't generate any ...
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10 votes

Why are oxygen requirements based on pressure altitude?

The air in the lungs is in pressure equilibrium with the cabin, but not temperature equilibrium. It's always at body temperature. So the only variable that can affect how much oxygen is available to ...
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9 votes
Accepted

Do modern airliners have oxygen sensors in the cabin?

The air conditioning system on board airliners is an open system: it scoops up air from the atmosphere, compresses it, expels it through the cabin vents, and then outflows it through discharge valves. ...
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9 votes

Why can't we use bleed air instead of oxygen cylinders?

In order to breathe normally, you need a minimum oxygen partial pressure in the air. Normally, this is provided by pressurizing the cabin to higher pressures than the outside air with bleed air, which ...
  • 49.6k
9 votes

With supplemental oxygen, what altitude can a pilot safely operate at?

Unacclimatized human needs around 14–15 kPa partial pressure of oxygen to breathe. Since total pressure is 15 kPa around 45,000 ft altitude, pressure suit is needed above that. Given that ...
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8 votes

Is flying at 14,000 MSL safe for children without supplemental oxygen?

There are always health implications at higher altitudes, even those approved by the FAA. Legally you are not prevented from flying at this altitude since the FAA does not stipulate an age for that ...
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8 votes

How do people suffering from hypoxia not realize they aren't getting enough oxygen?

The 'breathe faster and harder' is a cinema trope. One of the first things to go with hypoxia is judgement. Do you feel good? You cannot trust your assessment. As an impecunious glider pilot (not ...
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8 votes

How do people suffering from hypoxia not realize they aren't getting enough oxygen?

Apart from the points raised in other answers about breathing response being triggered by carbon dioxide in the blood, and the feeling of euphoria when hypoxic, there is also the fact that low blood ...
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7 votes
Accepted

Does hypoxia affect pilots differently from people on the ground?

The analogy that if someone can become acclimated to working at high altitudes and therefore should not need supplemental O2 in an airplane is flawed. While flying - at least straight and level - does ...
7 votes

Why are oxygen requirements based on pressure altitude?

Assuming our lungs are like our engines They are not. Engine (at least spark-ignited reciprocating one) uses most oxygen in each charge and its RPM is limited, so it can't be run faster to compensate ...
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7 votes
Accepted

Do pilots breathe the same air as passengers?

In General, Yes. As your image already shows, the same air is distributed throughout the cabin and the flight deck. For example, in the 737 NG FCOMv2 2.30.4 (Air Systems - Air Conditioning ...
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6 votes

Is there possibility to Survive without brain damage at 30/35,000 feet?

Long term, no, it is not. Any exposure to pressure altitudes over 26,000 ft will eventually cause death from hypoxia, even with acclimation to the higher altitudes. There is a period referred to as ...
6 votes

Do pilots get more fresh air than passengers?

Taking the B737 as an example, fresh air from the left pack flows directly into the cockpit (green airflow in the diagram), whereas the passenger cabin is served from the mix manifold only (yellow). ...
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6 votes

How much oxygen is put in say a 180-seater A319 or A320 aircraft?

An A320 carries oxygen generators for passengers and cabin crew, pressurized oxygen for flight crew (including observers) and some portable oxygen bottles [1]. I can't find the exact volume of the ...
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5 votes

What equipment qualifies as FAA-acceptable for providing "Supplemental Oxygen"?

An even more important question than how is how much oxygen to take, but there's no specific FAA guidance or regulation on either point. Different aircraft can carry different equipment, and people ...
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5 votes
Accepted

Passenger hypoxia in a small plane at 11,000 feet: what is the pilot's responsibility?

There is no regulatory requirement for oxygen to be available for anyone on board an aircraft so long as it remains at altitudes of 12,500' MSL or less. And only the required minimum flight crew is ...

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