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Pressurized aircraft have been around since World War II, with the Boeing B-29 Superfortress being an early example of an aircraft with a pressurized cockpit. Since then, technology has improved significantly, and the Airbus A350 boasts one of the world’s most advanced cabin pressurization systems. The Airbus A350 is the world’s youngest clean sheet commercial aircraft, having entered service three years after the Boeing 787. Like the Dreamliner, it benefits from its extensive usage of Carbon Fiber Reinforced Polymers.
The Airbus A380 Superjumbo is also noted for being a very comfortable aircraft, being very quiet, spacious, offering a smooth ride, and having a large cabin cross-section. However, from an engineering perspective, the A380 was more of a big aircraft than it was a next-generation aircraft. Today, the Airbus A350 and Boeing 787 Dreamliner form their own category as cleansheet modern widebody aircraft. Other updated aircraft, like the A330neo and Boeing 777X, may close the gap and benefit from their technologies, but it’s the A350 and 787 that offer the highest standard. This includes the world’s leading cabin pressure and cabin humidity.
How Cabin Pressurization Works
Commercial aircraft typically cruise at latitudes of between 30,000 and 40,000 feet. At that altitude, the outside air is too thin for humans to get enough oxygen. At an altitude of 40,000 feet, people will lose consciousness in approximately 15 to 20 seconds. During rapid decompression, oxygen masks drop so that people can survive, and the pilot will descend the aircraft to an altitude where people can breathe.
Separately, Airbus says, “Airbus developed an automatic system which, in the event of cabin pressurisation system failure, takes over from the crew and brings the aircraft back to an altitude where it is possible to breathe normally.” This is a safety mechanism that is not unique to the A350. To pressurize the cabin, high-pressure air is taken from the engine compressor stages (called bleed air) or from electronically driven compressors on the Boeing 787 Dreamliner.
Fresh and comfortable air is delivered into the cabin. Excess air is released through the aircraft’s outflow valves, which are normally located at the rear of the fuselage. The air is managed by the Environmental Control System (ECS), and the cabin pressure is kept at an equivalent pressure altitude of 6,000 to 8,000 feet. Older aircraft have pressures at around 8,000 feet, while the A350 (and 787) maintain pressures of around 6,000 feet.
A350 Remains Bleed-Air Unlike Boeing 787
The Airbus A350 is part of the same generation as the Boeing 787 Dreamliner and offers some of the greatest levels of comfort for commercial aircraft. It uses the traditional bleed-air system, just like most other Airbus and Boeing commercial aircraft. The A350’s bespoke Rolls-Royce Trent XWB engines supply compressed air from their high-pressure states, which is then cooled, conditioned, and fed into the cabin.
The main difference between the A350 and the Boeing 787 is that the 787 is ‘bleedless’ and does not use engine bleed air for its cabin pressurization. Instead, it uses the electric compressors mentioned above. Otherwise, the rest of the system works much the same way on the two jets with outflow valves, etc. Boeing selected the electric compressor system for its Dreamliner because it is deemed more fuel efficient and provides more precise control, although it comes with a weight penalty.
|
Widebody commercial aircraft |
Air source (per Airbus, Boeing) |
Typical cabin altitude (approx.) |
|---|---|---|
|
Airbus A330 |
Bleed air |
7,000-8,000 feet |
|
Airbus A350 |
Bleed air |
6,000 feet |
|
Airbus A380 |
Bleed air |
7,000-8,000 feet |
|
Boeing 787 |
Electric compressors |
6,000 feet |
|
Boeing 777X |
Bleed air |
6,000 feet |
For now, the Boeing 787 is the only bleedless widebody aircraft; even the upcoming Boeing 777X uses bleed air. Another major improvement of the A350 is that it increases the cabin humidity to around 20%, increasing passenger comfort and reducing dry eyes. Again, increased humidity is an advanced feature it shares with its Dreamliner rival.
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A New Airbus Standard Benefiting The A330neo
Airbus improvements to the cabin pressurization system include the A350 having more electronically assisted control and more precise pressure and flow modulation. A reduced bleed demand also results in increased engine efficiency. The A350 has high-efficiency heat exchangers and better digital controls that allow for smoother pressure changes. It is optimized around having a higher cabin pressure (equivalent to 6,000 feet) and higher humidity.
But it is the Cabin Pressure Control System (CPCS) where the A350 is significantly more advanced than Airbus’ other older jets. It is even able to match the cabin pressure with the destination elevation precisely. As Airbus designed its flagship A350, it also updated the A330 as the A330neo. The A330neo benefits from many of the A350’s innovations, but being a fundamentally older design with an aluminum fuselage, it is unable to match all of the A350’s cabin pressure and humidity performance.
The A330neo inherits new-generation bleed air systems, modernized ECS control, an upgraded Cabin Pressure Control System, some humidity improvements, but it doesn’t have the higher cabin pressure, the level of humidity, and other things. The Boeing 787’s bleedless system pulls in outside air. That air is hot and needs to be cooled through air-cycling machines, which also remove moisture and mix it with recirculated cabin air through the aircraft’s HEPA filters.
CFRP’s Are More Fatigue Resistant
The Airbus A350 makes extensive use of lightweight and extremely strong Carbon Fiber Reinforced Polymers (CFRP). These allow the aircraft to reduce its weight by up to 50% compared with the metals they replace, while also being more corrosion-resistant and durable. The lighter weight allows the aircraft to increase its fuel efficiency and increase its range. The only aircraft to rival the extensive use of CFRP is the Dreamliner; the updated 777X is increasing the amount of CFRP, but it will not rival the A350 or 787.
As these advanced materials are more corrosion resistant, it allows Airbus to increase the cabin humidity. As Airbus says, “Another benefit of the CFRP fuselage construction is the lower (6,000ft) cabin altitude pressure combined with improved humidity levels during cruise – leading to less overall passenger fatigue.”
One of the primary ways in which an aircraft ages is how many pressurization cycles it has. Every time an aircraft is pressurized, its fuselage is stressed. To mitigate the stress, older aircraft are pressurized to around 8,000 feet, or around the altitude of Aspen, Colorado. CFRPs have the advantage of having high fatigue resistance, allowing them to withstand the pressurization cycles better. This enables Airbus to increase the cabin pressure to around 6,000 feet.
Round Windows & 30 Years Of Service Life
Airbus’ other aircraft, like the A320, A330, and A380, come with aluminum fuselages, and these are more susceptible to metal fatigue and corrosion over repeated pressurization cycles and exposure to higher humidity levels. One of the points where aircraft are stressed the most is around the windows. The de Havilland Comet 1 was initially designed with square windows, and this led to fatigue concentrations and three aircraft catastrophic structural failures in mid-flight before the design flaw was identified. Since then, all aircraft windows have been round.
Composites allow aircraft to endure more pressurization cycles, and this should allow them to remain in service for longer. In reality, aircraft are often scrapped due to new aircraft being more fuel-efficient and rising maintenance costs than them coming to the end of their structural lives.
Long-haul widebody aircraft are also designed with the intention that they are pressurized less often than narrowbody aircraft. As widebody aircraft fly longer routes, they fly fewer cycles in a year. Both the A350 and 787 are designed to remain in service for between 25 and 35 years. That said, there is no cut-off point, and with proper maintenance, these aircraft are capable of remaining in service for more than 40 years.
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Airbus A350 Offers Top Contemporary Passenger Comfort
While the Airbus A350 uses the same bleed system as other aircraft, it is the aircraft’s CPRF fuselage and other advancements that allow it to maintain a higher cabin pressure and high humidity level. These provide a more comfortable environment for passengers, leading to fewer headaches, less ear discomfort from changing air pressure, less dry eyes (especially on long flights), and more. These cabin improvements help contribute to reducing symptoms associated with jet lag.
While jet lag is primarily caused by disrupting the body’s circadian rhythm by rapidly changing time zones, other factors, like general fatigue, also weigh in. The Airbus A350 continues to improve over time. Airbus’ new production standard introduces electro-dimmable windows that block 99.999% of light. This is the same technology as the windows found on the Dreamliner, although they will remain much smaller than the Dreamliner’s large windows.
The new production standard also increases the internal cabin width by four inches by making the walls thinner. That said, this may result in passengers having less personal room as airlines may be tempted to squish seats ten-abreast, up from the industry-standard nine-abreast. Even so, this can still benefit the passengers by reducing fares.
