A photo showing the aftermath of passengers forcibly prying down O2 masks on a flight due to smoke. They didn't understand it would not help them

Southwest 3923: Why Oxygen Masks Don’t Save You From Smoke in the Cabin

In March 2023, Southwest Airlines flight 3923, a Boeing 737 MAX en route to Fort Lauderdale from Havana, Cuba, made an emergency landing shortly after takeoff when the cabin began to fill with smoke secondary to an engine failure and fire from ingesting a turkey vulture into its right engine.1  For those unfamiliar, turkey vultures are fairly large birds, having a wingspan of 160–183 cm (63–72 in), are 62–81 cm (24–32 in) long, and can weigh up to 2.41 kg (5.3 lb).

One passenger on the flight told NBC News that other passengers had “bloody knuckles” from punching open the overhead oxygen mask covers. 2

PRO TIP: Airline oxygen masks do not filter air. Also, you may not want an open oxygen source when there is a possibility of fire.

O2 Masks: Designed for Hypoxia, Not Smoke

The FAA-approved “Dixie cup” oxygen masks will allow environmental air (and in this case, smoke) to enter the mask if the wearer takes a deep breath. They are not designed to prevent smoke from entering the mask.3

The oxygen masks provide “get me down” oxygen to prevent the passenger from becoming hypoxic if the aircraft undergoes significant decompression. They are not designed, nor are they likely to help in a smoke-filled cabin.

The Limitations of “Dixie Cup” Oxygen Masks
  • Designed to Prevent Hypoxia
  • Don’t Filter Fire or Fumes
  • Can provide additional oxygen fuel in the event of a cabin fire

Oxygen Can Become Fuel

Also, now that your fellow passengers have “taken the matter into their own hands,”2  they are releasing oxygen-mask oxygen into the passenger compartment. Although not necessarily a danger issue in a smoke-filled cabin, filling the cabin with additional oxygen could be catastrophic if there is a flame or fire inside the aircraft.

Why does the Turkey Vulture cause smoke?

In this case, the turkey vulture ingested into the engine resulted in an engine fan blade breaking, causing the turbine to become unstable and generate significant vibration. The 737 Max has a system that helps stabilize engine vibration from the missing fan blade, but as a byproduct, also allows engine oil to leak into the engine, which then combusts and vents toxic smoke into the cabin.

Cockpit vs Cabin: A Matter of Seconds

If the left engine were involved, it vents into the cockpit at much even higher volumes. The FAA agreeds after a toxicology analysis of the smoke, it would be toxic to pilots in the cockpit in 39 seconds. In a larger passenger cabin, the effects are greatly reduced because of the cabin volume.  To date there have been two events where this has happened, both in 2023 with the 737 MAX.4,5
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References

1 https://asn.flightsafety.org/wikibase/308914
2 https://www.foxbusiness.com/lifestyle/southwest-airlines-flight-fort-lauderdale-fills-smoke-returns-cuba-emergency-landing
3 DOT/FAA/AM-21/11 Passenger Oxygen Mask Design Study, March, 2021
4 NTSB Aviation Investigation Preliminary Report DCA24LA330
5 NTSB Aviation Investigation Report AIR-25-03 June 18, 2025
Mike Shertz MD/18D

Dr. Mike Shertz is the Owner and Lead Instructor at Crisis Medicine. Dr. Shertz is a dual-boarded Emergency Medicine and EMS physician, having spent over 30 years gaining the experience and insight to create and provide his comprehensive, science-informed, training to better prepare everyday citizens, law enforcement, EMS, and the military to manage casualties and wounded in high-risk environments. Drawing on his prior experience as an Army Special Forces medic (18D), two decades as an armed, embedded tactical medic on a regional SWAT team, and as a Fire Service and EMS medical director.

Using a combination of current and historical events, Dr. Shertz’s lectures include relevant, illustrative photos, as well as hands-on demonstrations to demystify the how, why, when to use each emergency medical procedure you need to become a Force Multiplier for Good.

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