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Do pilots breathe the same quality of air as passengers ?
(i.e. identical parameters: same O2, CO2 and O3 levels, same temperature, same humidity, etc.)

Do pilots breath the same air as passengers (shared air) ?
(i.e. the air a passenger exhales will be inhaled by the pilot [or vice verca], which also means that smoke in the cabin will inevitably end up in the cockpit)

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  • $\begingroup$ what makes you think that this could not be the case? on which aircraft models? $\endgroup$
    – Federico
    Commented Dec 11, 2018 at 8:18

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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 Description) it says:

Since the flight deck requires only a fraction of the air supply provided by the left pack, most of the left pack air output is mixed with the right pack supply and routed to the passenger cabin.

So on the 737, the left pack supplies air to the flight deck and the cabin, the right pack only to the cabin (in normal operations).

Air from the cabin is also reused in the recirculation system:

The recirculation fan system reduces the air conditioning system pack load and the engine bleed air demand. Air from the passenger cabin and electrical equipment bay is drawn to the forward cargo bay where it is filtered and recirculated to the mix manifold. The fan is driven by an AC motor. The fan operates with the recirc fan switch in AUTO except with both packs on and one or both in HIGH.

This implies, air previously exhaled by a passenger could make its way into the flight deck, but it is filtered first. In case of smoke in the cabin, the recirculation system would be switched off. However, during normal operations, the left pack supplies the flight deck directly:

737 Mix Manifold (source: 737 NG FCOMv2 2.30.4)

All air quality parameters you mentioned should be identical or very similar for the flight deck and the cabin, except for temperature. Most aircraft allow separate temperatures for different zones. E.g. the 737 again:

There are three zones: flight deck, forward cabin and aft cabin. Desired zone temperature is set by adjusting the individual Temperature Selectors. The selector range is approximately 65°F (18°C) to 85°F (30°C). The packs produce an air temperature that satisfies the zone which requires the

Temperature Selectors in the 737 overhead panel:

737 Temperature Selectors (source: 737 NG FCOMv2 2.30.4)

The details will of course depend on the exact aircraft model!

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No, they do not. The pilots in the flight deck zone receive 100% fresh conditioned air directly from the left pack. The rest of the conditioned left pack air will be collected in the mix manifold for distribution for passengers. Recirculation fans will recirculate cabin air back to the mix manifold. Since the F/D isn't receiving air from the mix manifold, they aren't receiving recirculated, stale cabin air.

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    $\begingroup$ This answer would benefit from some references. $\endgroup$
    – 0xdd
    Commented Jul 15, 2019 at 19:55
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    $\begingroup$ Surely this would depend on the design of the particular aircraft? In my Cherokee, for instance, passengers generally breathe the same air I do - whatever leaks in or comes in through the heater - unless I open the little vent window on the pilot's side. $\endgroup$
    – jamesqf
    Commented Jul 15, 2019 at 20:14
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    $\begingroup$ For a 737, this answer is incorrect. Even with the left pack supplying the flight deck, you still get some amount of recirculated air, as demonstrated by the decrease in airflow to the cockpit when the recirc fan is switched off. The pilots get a greater proportion of their air straight from the pack than the passengers do, but it's not separated. If it were, the checklist for smoke-in-the-cabin wouldn't have pilots putting on oxygen masks & smoke goggles! $\endgroup$
    – Ralph J ♦
    Commented Jul 15, 2019 at 20:28
  • $\begingroup$ @RalphJ OP asks if the quality is the same. The amount of recirculation has effect on the quality, correct? $\endgroup$
    – Koyovis
    Commented Jul 15, 2019 at 22:45
  • $\begingroup$ +1, the answer is correct $\endgroup$
    – Koyovis
    Commented Jul 15, 2019 at 22:53

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