Do pilots get more fresh air than passengers? [duplicate]

This question already has an answer here:

There is a famous air travel myth claiming that "pilots get more fresh air than passengers".

(source: The pure cure, p.375)

I would like experts to either dispel or confirm this myth, that pilots receive "better air" with higher oxygen levels than passengers, who have to breathe more recirculated air.

Although at first glance it might sound absurd, but when you think about it, it would actually make sense, because:

• The worst thing that can happen to passengers is that they get tired. Sure, that may be unpleasant (think of the stale air in a crowded room), but does not pose a health or security risk.

• Pilots, on the other hand, need to be wide awake and perform to the top of their abilities, as errors can be fatal. So any negative outside influences on pilot performance needs to be eliminated. In particular, pilot fatigue significantly increases the risk of pilot error.

However "CO2 levels directly affect pilots’ flight performance" as was tested in a study on 30 active commercial airline pilots performing maneuvers under varying carbon dioxide concentrations:

press release
Previous research led by Allen and colleagues found that, in office buildings, CO2 concentrations between 1000-2500 ppm – levels once thought to be benign – negatively impact the cognitive function of employees. For the new study, they wanted to determine if higher CO2 levels on the flight deck would impair a pilot’s ability to perform advanced maneuvers and manage emergency situations, such as a single-engine failure during takeoff. […] Average CO2 levels on the flight deck are less than 800 ppm. However, they have been measured as high as 2000 ppm on the flight deck and even higher in the cabin during the boarding process. […] The National Research Council has suggested that current standards for ventilation rates on flight decks may be inadequate.

background
On the flight deck […] the average CO2 concentrations are typically <1000 ppm, but the 95th percentile concentration can be as high as 1400 ppm, depending on airplane type.

results
Compared to segments at a CO2 concentration of 2500 ppm, the odds of passing a maneuver as rated by the Examiner in the simulator were 1.52 times higher when pilots were exposed to 1500 ppm and 1.69 times higher when exposed to 700 ppm.

In light of the above it would make sense to prioritize pilots over passengers when it comes to circulation of fresh air.

I will post the results of my research into this question as an answer below, but would welcome other answers presenting technical evidence and quoting citable references.

scope:
This is not the same question as Q57941.
Q57941 asks if there is airflow between cockpit and cabin (as opposed to be hermetically sealed).
Whereas this question asks if more fresh air from OUTSIDE flows into the cockpit than into the cabin. Also, it addresses a very famous airline myth, and as such it has a valuable purpose.

marked as duplicate by Pondlife, Ralph J, xxavier, kevin, foootDec 12 '18 at 15:35

• – Dan Pichelman Dec 11 '18 at 18:38
• The statement that pilots can get 10x more oxygen than pax, on its own, does not make sense. A 10x difference would either mean the pilots are breathing 100% $O_2$, which is just not necessary, or the passengers are beginning to die. The only extenuating case where it might be true is during an emergency descent where the oxygen masks have dropped, and only long enough to get down to 10,000 ft. – abelenky Dec 11 '18 at 20:22
• @abelenky: You are talking about a 10x higher oxygen concentration in the air. I don't think this is the claim, but rather 10x higher airflow (and thus oxygen flow) per person, e.g. 10 CFMP (ft³/min per person) in the cabin and 100 CFMP in the cockpit. – summerrain Dec 11 '18 at 20:40
• Note in particular that while this has an alleged endnote citation, Ms. Fairechild is not actually quoted but paraphrased. – chrylis Dec 11 '18 at 22:11
• @summerrain If that's what they meant to claim, then saying "ten times more oxygen" is a really strange way to say it. I was thinking the same thing as abelensky when I read that. – reirab Dec 11 '18 at 22:35

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). Therefore

share of re-circulated air (red) in the cabin ventilation air (yellow):

B737: pilots 0% passengers 25%
B757: pilots 0% passengers 50%
B767: pilots 0% passengers 50%
B777: pilots 0% passengers  ?


In a cabin packed with hundreds of people each transforming 21% O2 and 0.04% CO2 into 16% O2 and 4% CO2 (i.e. breathing) and where 50% of this exhaled used air (red) is recirculated back into the cabin (yellow), O2 and CO2 levels are poorer than in the cockpit not supplied with exhaled used air.

The AFA-CWA flight attendants association indicates how much fresh air each person receives:

• How much air is supplied in the economy section? 6-10 ft³/min of outside air to each person which is about half what is recommended in buildings and transportation vehicles.
• The cockpit gets 50-100 ft³/min per person of outside air, or sometimes a mix of outside and recirculated air depending on the aircraft type. That is up to 20 times more than in the passenger cabin.
• It's actually a minority of the left pack air going to the flight deck; maybe a third of so. The bulk of it is going to the cabin to supplement the right pack, being the less restrictive path. Not to say the air quality still isn't better up front. – John K Dec 11 '18 at 18:38
• In other words 33% of the fresh air from the left pack is for 2 persons only. – summerrain Dec 11 '18 at 20:57
• @summerrain the two people are V.I.P.s... – Harper Dec 11 '18 at 22:13
• Yeah, insofar as bad air can make you a bit sleepy, I'd much rather doze off in the middle of my book than have the pilot so much as think about needing another coffee. – yshavit Dec 12 '18 at 4:04
• @Harper. Yes, but the question is not about why they get more fresh air, but do they. – Penguin Dec 12 '18 at 10:29

I can confirm that similar air distribution systems also exist for:

• Boeing 777:

The flight deck receives 100% fresh conditioned air from the left pack. The flight deck is maintained at a slightly higher pressure than the passenger cabin to prevent smoke and objectionable odors from entering the flight deck.

(source: 777-200 FCOMv2 2.20.3 Air Systems - Air Conditioning System Description)

• Boeing 747: Pack 1 directly supplies the flight deck: (source: 747-400 FCOMv2 2.20.4 Air Systems - Air Conditioning System Description)

(source: 747-8 FCOMv2 2.20.5 Air Systems - Air Conditioning System Description)

This is, however, not the case for the following aircraft:

• Airbus A320: The mixing unit supplies air to the flight deck and passenger cabin equally: (source: A320 FCOM 1.21.10 Air Conditioning)

In the end it depends on the aircraft type. It seems on Boeing aircraft the flight deck air is indeed fresher than the cabin air because it receives no recirculated air (during normal operations).

However, it is not clear what "ten times more oxygen" is supposed to mean in the article. It certainly does not mean a ten times higher oxygen concentration (as already noted in the comments). A ten times higher flow rate would not impact the available oxygen partial pressure either.

• Great answer! – I only disagree with the last sentence. Of course if you are in a cabin packed with hundreds of people all consuming oxygen and exhaling carbon dioxide, and 50% of the exhaled used air is recirculated back into the cabin, then of course the O₂ and CO₂ levels will be poorer than in the cockpit. – summerrain Dec 13 '18 at 4:21