What happens if an airliner suddenly loses cabin pressure?
Let's just say it's not like it is in the movies.
- By Rebecca Maksel
- AirSpaceMag.com, September 24, 2009
Airliners carry their own portable atmosphere. How much can they afford to lose? Aaron Escobar/Flickr/Creative Commons
It may have been speculation about the cause of the Air France Flight 447 crash this summer that led Faithe Silver, of Tampa, Florida, to ask: “How often do commercial airliners experience cabin depressurization in flight?”
We assume Ms. Silver doesn’t mean the ordinary pressurization and depressurization that happens on every flight after takeoff and before landing. She wants to know what happens if the cabin rapidly depressurizes. Is it as dramatic as in the movies?
Pilot and author David Lombardo writes in his book Advanced Aircraft Systems: “Hollywood has fostered an image of rapid cabin depressurization that has come to be known as explosive decompression. Someone on the ground shoots a hole into the side of an aircraft and it results in total loss of cabin pressure with paper, food trays, and baggage flying everywhere.”
Right, that’s what we’re talking about.
“Reality simply does not work that way,” explains Lombardo. “A bullet hole in a cabin wall would have no perceived effect on cabin pressure…. A bullet hole is far smaller than the opening of the outflow valve [through which cabin air escapes during routine depressurization]. In fact, such a hole would account for less air leakage than what is normally lost around door and window seals.”
That’s not to say sudden decompression isn’t a danger. The FAA (in its Advisory Circular 61-107A) provides a helpful chart showing just how long crewmembers are able to perform flight duties with an insufficient supply of oxygen. In an aircraft at 22,000 feet, passengers and crew would have 5 minutes of “useful consciousness” after rapid decompression. But at 43,000 feet, the time drops to a mere 5 seconds, hardly long enough to don an oxygen mask. (The same circular notes “One pilot does not need to wear and use an oxygen mask if both pilots are at the controls and each pilot has a quick donning type of oxygen mask that can be placed on the face with one hand from the ready position and be properly secured, sealed, and operational within 5 seconds. If one pilot of a two-pilot crew is away from the controls, then the pilot that is at the controls must wear and use an oxygen mask that is secured and sealed.”)
To see how oxygen deprivation affects the brain, take a look at this PBS feature about climbers scaling Mount Everest. Subjects were tested at various stops along the summit. (As a control, they were tested at base camp as well.) Tests included simple verbal puzzles (“If I say that Jack stole Ann’s ball, who is the thief?”), and sentence repetition. Climbers did fine at sea level, but as they reached higher altitudes, they found it difficult to answer even simple questions.
NASA Technical Report CR-1223, which gives the lowdown on “Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects,” includes a review of “human accidents involving explosive decompression.” The effects are unpleasant, to say the least. After regaining consciousness, subjects reported a feeling of unsteadiness “like being drunk,” lingering pains in the chest “like after a K.O.,” and intense throat pain.
On July 13, 2009, a Southwest Airlines Boeing 737-300 (Flight 2294) depressurized after a one-foot hole appeared in its upper fuselage (an accident investigation is under way). The aircraft, en route to Baltimore from Nashville, was diverted to Charleston, West Virginia, where it landed safely. The cabin depressurized about 30 minutes into the flight at 34,000 feet, and no injuries were reported, although the NTSB noted “The damage left a hole measuring approximately 17 inches by 8 inches.”
In the event of a larger hole in the fuselage, there’s more risk of hypothermia than decompression. “[T]he cabin temperature would drop from 70˚ degrees F to as low as -60˚F,” writes Lombardo. “With temperatures that low, it is only a matter of seconds before hypothermia sets in and everyone begins to freeze to death.”
So it isn't the pressure drop that gets you after all. It's the cold.
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Comments (6)
Does the space shuttle produce a sonic boom at launch? Would you hear it at ground zero or is there a cone of silence?
Posted by Rocky on January 18,2010 | 09:48 AM
A sonic boom is much quieter than rocket engines.
Posted by Mike Schwab on March 7,2010 | 09:44 PM
On 3 November 1973 on a National Airlines DC10, the number one engine exploded and a piece shattered a window and a passenger as ejected from the aircraft.
The plane made an emergency descent to Albuquerque
Posted by GeorgeK on September 17,2010 | 01:01 PM
Sudden decompression has caused aircraft loss in the past. On military C141 and C5 sudden failure of the aft pressure door has caused the floor above the cargo compartment to buckle and fracture the tail controls leaving only the throttles for pitch control. I believe it has also happened on DC10's and 747's as I seem to remember a Japanese 747 roaming around Japan for an hour or so before crashing.
Posted by Frederick R Cole on November 10,2010 | 12:03 PM
What happened to the Aloha airlines 737 with the 15 foot of upper cabin loss at fl 26oft? the only people that perished were those closest to the hole and not secured, and a flight attendant.
this accident was caused by not paying attention to how
aircraft are stripped and repainted.
Posted by axel orton on November 28,2010 | 09:49 PM
No passengers were kileld in the Aloha accident. One flight attendant was blown out of the aircraft.
I've experienced two explosive decompressions during Canadian air force high altitude indoctrination training in a decompression chamber so I could fly as a passenger in fighters. We went from 5000 feet to 18,000 feet in 1/4 of a second. The air turned white due to condensation of moisture in the air and the thick steel walls of the chamber made a loud bang as they flexed. We set our oxygen panel controls to 100% oxygen and emergency (positive pressure breathing) and then waited for the instructors to make sure we were all OK (we were) and then they slowly brought us back down to sea level.
We also were taken to 25,000 feet and using the buddy system, half of us took off our masks and had to copy drawings on a small clipboard. They were squares, triangles, circles, etc. The idea was to watch for signs of hypoxia because different people have different initial symptoms and when you're wearing an oxygen mask and gloves, you can't see if your lips and fingertips turn blue. When we detected the symptoms, we put our mask back on and then our partners had their turn.
A few people decided to see how long they could last, which wasn't the idea of the test, and they got pretty stupid pretty fast.
The instructors told us before my second HAI course that members of a Canadian expedition to Everest had spent extended periods in the chamber at 25,000 feet to prepare themselves for the ascent. Rather them than me.
Posted by Jeff Rankin-Lowe on January 31,2012 | 11:23 PM