Xrfgtjtk

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.

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

• pilots receive 100% fresh air


• while passengers receive a mix of 50% fresh air and 50% re-circulated cabin air on average, across all aircraft types

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.

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)

  
  
  

  

  
  
  
  
  
  • 
    Bombardier Dash-8 Q400:
    
    (source: smartcockpit.com)
  
  
  
  

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.