How high can a plane fly without a pressurized cabin?

For operations conducted under Parts 121 and 135, the flight crew must use oxygen when cabin altitudes are above 10,000 up to 12,000 feet after 30 minutes and at all times when above 12,000 feet. The general aviation pilot flying an unpressurized airplane will not normally operate above 25,000 feet.



In the world of aviation, the altitude limit for unpressurized aircraft is primarily dictated by human physiology and legal regulations rather than the mechanical capability of the airframe itself. Under standard FAA Part 91 regulations, pilots can fly up to 12,500 feet Mean Sea Level (MSL) without supplemental oxygen for up to 30 minutes. Once you exceed 14,000 feet, the flight crew must use supplemental oxygen at all times, and above 15,000 feet, every occupant in the aircraft must be provided with it. Physically, the "physiological ceiling" is generally considered to be around 25,000 feet for unpressurized flight with standard oxygen equipment; beyond this point, the risk of hypoxia and decompression sickness increases exponentially. Flying higher than 25,000 feet in an unpressurized vessel is extremely rare and dangerous, as it requires specialized pressure-demand oxygen systems to force air into the lungs. By 34,000 feet, even breathing 100% oxygen is equivalent to breathing sea-level air, making any further ascent without a pressurized environment life-threatening.

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The higher the altitude, the less oxygen there is in the air and the lower the overall air pressure is. If flights were not pressurized, passengers would be at risk of various physiological aliments. Because of this, federal regulations require that all commercial flights over 8,000 feet be pressurized.

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The primary problem is low oxygen, says Professor Frances Ashcroft, a physiologist at Oxford University. Low pressure would cause little more than discomfort in the ears and eyes, but the associated drop in oxygen levels makes people pass out if they do not put their oxygen masks on within about 15 seconds.

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Importance to Members Sure, everyone knows that you have to use supplemental oxygen if you fly more than 30 minutes at cabin pressure altitudes of 12,500 feet or higher. And that at cabin altitudes above 14,000 feet pilots must use oxygen at all times.

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On the ground, the airplane is unpressurized and the outflow valve is wide open. During preflight, the pilot sets the cruise altitude on a cabin pressure controller. As soon as the weight is off the main wheels at takeoff, the outflow valve begins to close and the cabin starts to pressurize.

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When an aircraft experiences turbulence, the plane can drop or change altitude suddenly. This is why pilots always caution passengers to buckle up and stay seated when they are experiencing flight turbulence. The sudden movements put passengers at risk.

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The air on a plane contains less oxygen than the air we normally breathe in. This leads to lower levels of oxygen in the blood. If you do not have a lung condition, the drop in oxygen is not enough that you would feel the difference.

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The Cabin Altitude of a pressurised aircraft is normally maintained at and altitude of 8,000 ft or less as a compromise between the physiological needs of the crew and passengers and the structural limitations of the aircraft. At 8,000 ft the use of supplemental oxygen is not required.

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The biggest reason for flying at higher altitudes lies in fuel efficiency. The thin air creates less drag on the aircraft, which means the plane can use less fuel in order to maintain speed. Less wind resistance, more power, less effort, so to speak.

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Air is less dense at high altitudes than low altitudes. At ground level, the air pressure is a little over 14 pounds per square inch (PSI). When an airplane reaches its typical cruising altitude — usually about 30,000 to 40,000 feet — the air pressure may be just 4 to 5 PSI.

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On most long haul aircraft there are hidden beds where the pilots and Cabin Crew are able to sleep out of the view of passengers. Some long haul flights require there to be 3 or 4 pilots due to the length of the flight and to allow a suitable sleep/rest opportunity for the pilots.

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On many aircraft types, pilots can open the side windows in the cockpit. The main reason for this is not for ventilation or vision; it is related to aircraft safety law.

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Many airlines provide crew rest areas on their aircraft, where pilots can sleep during long-haul flights. These areas are usually located in the tail, cargo area or above the cabin of the plane and are designed to be as quiet and comfortable as possible. Other crew members prefer to use business class seats to rest.

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While fuel dumps don't happen every day, they're also not uncommon. Nor do they usually represent a major emergency. In fact if an aircraft is taking the time to dump fuel before landing, that's likely an indication that the issue forcing the plane to land is serious but not critical.

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This is called a holding pattern. A holding pattern is a manoeuvre flown by pilots awaiting further clearance onto the next stage of their route, or into an airport. Essentially, they are used to safely organize and manage the flow of aircraft waiting to land.

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