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63-402: The systems described below are specific to current production Boeing airliners, although the details are essentially identical for passenger jets from Airbus and other companies. An exception was Concorde which had a supplementary air supply system fitted due to the higher altitudes at which it flew, and also the slightly higher cabin pressure it employed. On jetliners , air is supplied to

126-435: A 737-700 originally ordered by Southwest Airlines (Boeing customer code H4). Codes do not change for aircraft transferred from one airline to another. Unlike other models, the 787 uses a single digit to designate the series, for example, 787-8. This convention was followed in the development of the newest version of the 747, the 747-8, along with the 737 MAX and 777X series. Additional letters are sometimes appended to

189-469: A HEPA filter in a vacuum cleaner to be effective, the vacuum cleaner must be designed so that all the air drawn into the machine is expelled through the filter, with none of the air leaking past it. This is often referred to as "Sealed HEPA" or sometimes the more vague "True HEPA". Vacuum cleaners simply labeled "HEPA" may have a HEPA filter, but not all air necessarily passes through it. Finally, vacuum cleaner filters marketed as "HEPA-like" will typically use

252-403: A HEPA filter is working efficiently, the filters should be inspected and changed at least every six months in commercial settings. In residential settings, and depending on the general ambient air quality, these filters can be changed every two to three years. Failing to change a HEPA filter in a timely fashion will result in it putting stress on the machine or system and not removing particles from

315-476: A cabin altitude. The new airliners such as the Airbus A350 and Boeing 787 will have lower maximum cabin altitudes which help in passenger fatigue reduction during flights. The atmosphere at typical jetliner cruising altitudes is generally very dry and cold; the outside air pumped into the cabin on a long flight has the potential to cause condensation which might in turn cause corrosion or electrical faults, and

378-507: A combination mechanical blower and air purifier unit, which incorporated cellulose-asbestos paper in a deeply-pleated form with spacers between the pleats. It was referred to as an "absolute" air filter and laid the groundwork for further research to come in developing the HEPA filter. The next phase of the HEPA filter was designed in the 1940s and was used in the Manhattan Project to prevent

441-504: A fairly substantial breeze. Gaspers usually receive their air from the AC PACKs aboard the aircraft, which in turn receive compressed, clean air from the compressor stages of the aircraft's jet engines or when on the ground from the auxiliary power unit (APU) or a ground source. A master control for gaspers is located in the cockpit; gaspers are often temporarily turned off during certain phases of flight (e.g. during take-off and climb) when

504-402: A fiber) through a combination of the following three mechanisms: Diffusion predominates below the 0.1 μm diameter particle size, whilst impaction and interception predominate above 0.4 μm. In between, near the most penetrating particle size (MPPS) 0.21 μm, both diffusion and interception are comparatively inefficient. Because this is the weakest point in the filter's performance,

567-489: A filter of a similar construction to HEPA, but without the filtering efficiency. Because of the extra density of a true HEPA filter, HEPA vacuum cleaners require more powerful motors to provide adequate cleaning power. Some newer models claim to be better than the earlier ones with the inclusion of "washable" filters. Generally, washable true HEPA filters are expensive. A high-quality HEPA filter can trap 99.97% of dust particles that are 0.3 microns in diameter. For comparison,

630-439: A human hair is about 50 to 150 microns in diameter. So, a true HEPA filter is effectively trapping particles several hundred times smaller than the width of a human hair. Some manufacturers claim filter standards such as "HEPA 4," without explaining the meaning behind them. This refers to their Minimum Efficiency Reporting Value (MERV) rating. These ratings are used to rate the ability of an air cleaner filter to remove dust from

693-446: A hyphen and three digits that represent the series within the model, for example, 707-320 or 747-400 . In aviation circles, a more specific model designation is sometimes used where the last two digits of the series designator are replaced by the two-digit, alpha-numeric Boeing customer code , for example, 747-121, representing a 747-100 originally ordered by Pan American World Airways (Boeing customer code 21) or 737-7H4, representing

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756-476: A narrow convoluted pathway through which air passes. When the largest particles are passing through this pathway, the bundles of fibers behave like a kitchen sieve which physically blocks the particles from passing through. However, when smaller particles pass with the air, as the air twists and turns, the smaller particles cannot keep up with the motion of the air and thus they collide with the fibers. The smallest particles have very little inertia and move randomly as

819-510: A particular customer. HEPA HEPA ( / ˈ h ɛ p ə / , high efficiency particulate air ) filter, also known as a high efficiency particulate arresting filter, is an efficiency standard of air filters . Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through—at least 99.95% ( ISO , European Standard) or 99.97% ( ASME , U.S. DOE ) of particles whose diameter

882-447: A pre-filter (usually carbon-activated) to extend the usage life of the more expensive HEPA filter. In such setup, the first stage in the filtration process is made up of a pre-filter which removes most of the larger dust, hair , PM10 and pollen particles from the air. The second stage high-quality HEPA filter removes the finer particles that escape from the pre-filter. This is common in air handling units . HEPA filters, as defined by

945-405: A result of collisions with individual air molecules ( Brownian motion ). Because of their movement, they end up crashing into the fibers. Key factors affecting its functions are fiber diameter, filter thickness, and face velocity, which is the measured air speed at an inlet or outlet of a heating ventilation and air conditioning (HVAC) system. Face velocity is measured in m/s and can be calculated as

1008-525: A sub-zero bootstrap CAU, the moisture is extracted before it reaches the turbine so that sub-zero temperatures may be reached. The temperature of the PACK outlet air is controlled by the adjusting flow through the ram-air system (below), and modulating a temperature control valve (TCV) which bypasses a portion of the hot bleed air around the ACM and mixes it with the cold air downstream of the ACM turbine. The ram-air inlet

1071-429: A turbo-charger unit, the compressor and turbine are on a single shaft. The energy extracted from the air passing through the turbine is used to power the compressor. The air flow then is directed to the reheater before it passes to the condenser to be ready for water extraction by water extractor. The air is then sent through a water separator, where the air is forced to spiral along its length and centrifugal forces cause

1134-519: Is a division of the Boeing Company . It designs , assembles, markets, and sells commercial aircraft, including the 737 , 767 , 777 , and 787 , along with freighter and business jet variants of most. The division employs nearly 35,000 people, many working at the company's division headquarters in Renton, Washington or at more than a dozen engineering, manufacturing, and assembly facilities, notably

1197-416: Is a small scoop, generally located on the wing-to-body fairing. Nearly all jetliners use a modulating door on the ram-air inlet to control the amount of cooling airflow through the primary and secondary ram air heat exchangers. To increase ram-air recovery, nearly all jetliners use modulating vanes on the ram-air exhaust. A ram-air fan within the ram system provides ram-air flow across the heat exchangers when

1260-422: Is also able to capture some viruses and bacteria which are ≤0.3 μm. A HEPA filter is also able to capture floor dust which contains bacteroidia , clostridia , and bacilli . HEPA was commercialized in the 1950s, and the original term became a registered trademark and later a generic trademark for highly efficient filters. HEPA filters are used in applications that require contamination control , such as

1323-404: Is at low pressure (low thrust or high altitude), the air is drawn from the highest pressure bleed port. As pressure is increased (more thrust or lower altitude) and reaches a predetermined crossover point, the high pressure shut-off valve (HPSOV) closes and air is selected from a lower pressure port to minimize the fuel performance loss. The reverse happens as engine pressure decreases. To achieve

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1386-595: Is derived, defines several classes of filters by their retention at the given most penetrating particle size (MPPS): Efficient Particulate Air filters (EPA), High Efficiency Particulate Air filters (HEPA), and Ultra Low Particulate Air filters (ULPA). The averaged efficiency of the filter is called "overall", and the efficiency at a specific point is called "local": See also the different classes for air filters for comparison. For respirators , MSHA and NIOSH define HEPA as filters blocking ≥ 99.97% of 0.3 micron DOP particles, under 30 CFR 11 and 42 CFR 84. Since

1449-535: Is equal to 0.3  μm , with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm. HEPA filters capture pollen , dirt , dust , moisture , bacteria (0.2–2.0 μm), viruses (0.02–0.3 μm), and submicron liquid aerosol (0.02–0.5 μm). Some microorganisms , for example, Aspergillus niger , Penicillium citrinum , Staphylococcus epidermidis , and Bacillus subtilis are captured by HEPA filters with photocatalytic oxidation (PCO). A HEPA filter

1512-457: Is needed to drive the air through the system, but it is desired to use as low a supply pressure as possible, because the energy the engine uses to compress the bleed air is not available for propulsion, and fuel consumption suffers. For this reason, air is commonly drawn from one of two (or in some cases such as the Boeing 777 , three) bleed ports at different compressor stage locations. When the engine

1575-422: Is preferred over vapor cycle devices because of reduced weight and maintenance requirements. Most jetliners are equipped with PACKs Meaning of abbreviation see here . The location of the air conditioning (AC) PACK(s) depends on the design of the aircraft. In some designs, they are installed in the wing-to-body fairing between the two wings beneath the fuselage . On other aircraft ( Douglas Aircraft DC-9 Series )

1638-450: Is technology that uses air filters, such as HEPA filters, to remove pollutants from the air either indoors or in vehicles. Pollutants include smoke, viruses, powders , etc., and can originate either outside or inside. HVAC is used to provide environmental comfort and in polluted cities to maintain health. Modern airliners use HEPA filters to reduce the spread of airborne pathogens in recirculated air. Critics have expressed concern about

1701-472: Is thus eliminated. Consequently, when humid air at lower altitudes is encountered and drawn in, the ECS dries it through the warming and cooling cycle and the water separator mentioned above, so that even with high external relative humidity, inside the cabin it will usually be not much higher than 10% relative humidity. Although low cabin humidity has health benefits of preventing the growth of fungus and bacteria ,

1764-411: The Boeing 707 in 1957, except the Boeing 720 , Boeing's naming system for commercial airliners has taken the form of 7X7 (X representing a number). All model designations from 707 through 787 have been assigned, leaving 797 as the only 7X7 model name not assigned to a product. For models 707 to 777 , the full model number consists of an airplane's model number, for example, 707 or 747 , followed by

1827-675: The Everett Factory and Renton Factory (both outside of Seattle ), and the South Carolina Factory . It includes the assets of the Douglas Aircraft division of the former McDonnell Douglas Corporation, which merged with Boeing in 1997. As of the end of 2021, BCA employed about 35,926 people. Boeing Commercial Airplanes (BCA) is organized as: BCA subsidiaries: In November 2016, Boeing announced that Ray Conner would step down immediately as BCA's president and CEO. He

1890-520: The AC PACKs are located in the tail. The aircraft PACKs on the McDonnell Douglas DC-10 / MD-11 and Lockheed L-1011 are located in the front of the aircraft beneath the flight deck . Nearly all jetliners have two PACKs, although larger aircraft such as the Boeing 747 , Lockheed L-1011 , and McDonnell-Douglas DC-10/ MD-11 have three. The quantity of bleed air flowing to the AC pack is regulated by

1953-430: The ECS by being bled from a compressor stage of each gas turbine engine , upstream of the combustor . The temperature and pressure of this bleed air varies according to which compressor stage is used, and the power setting of the engine. A manifold pressure regulating shut-off valve (MPRSOV) restricts the flow as necessary to maintain the desired pressure for downstream systems. A certain minimum supply pressure

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2016-499: The ECS of some aircraft to keep relative humidity from extremely low levels, consistent with the need to prevent condensation. Furthermore, the Boeing ;787 and Airbus A350, by using more corrosion-resistant composites in their construction, can operate with a cabin relative humidity of 16% on long flights. The bleed air comes from the engines but is bled from the engine upstream of the combustor. Air cannot flow backwards through

2079-677: The HEPA specifications use the retention of particles near this size (0.3 μm) to classify the filter. However it is possible for particles smaller than the MPPS to not have filtering efficiency greater than that of the MPPS. This is due to the fact that these particles can act as nucleation sites for mostly condensation and form particles near the MPPS. HEPA filters are designed to arrest very fine particles effectively, but they do not filter out gasses and odor molecules. Circumstances requiring filtration of volatile organic compounds , chemical vapors, or cigarette , pet or flatulence odors call for

2142-416: The HEPA standard and may not have been tested in independent laboratories. Although such filters may come reasonably close to HEPA standards, others fall significantly short. In general terms (and allowing for some variation depending on factors such as the air-flow rate, the physical properties of the particles being filtered, as well as engineering details of the entire filtration-system design and not just

2205-549: The United States Department of Energy (DOE) standard adopted by most American industries, remove at least 99.97% of aerosols 0.3 micrometers (μm) in diameter. The filter's minimal resistance to airflow, or pressure drop , is usually specified around 300 pascals (0.044 psi) at its nominal volumetric flow rate . The specification used in the European Union : European Standard EN 1822-1:2019, from which ISO 29463

2268-401: The air as it passes through the filter. MERV is a standard used to measure the overall efficiency of a filter. The MERV scale ranges from 1 to 16, and measures a filter's ability to remove particles from 10 to 0.3 micrometer in size. Filters with higher ratings not only remove more particles from the air, but they also remove smaller particles. Heating, ventilation, and air conditioning (HVAC)

2331-474: The air properly. Additionally, depending on the gasketing materials chosen in the design of the system, a clogged HEPA filter can result in extensive bypassing of airflow around the filter. HEPA filters are critical in the prevention of the spread of airborne bacterial and viral organisms and, therefore, infection . Typically, medical use HEPA filtration systems also incorporate high-energy ultraviolet light units or panels with anti-microbial coating to kill off

2394-556: The aircraft is on the ground. Nearly all modern fixed-wing aircraft use a fan on a common shaft with the ACM, powered by the ACM turbine. The AC PACK exhaust air is ducted into the pressurized fuselage, where it is mixed with filtered air from the recirculation fans, and fed into the mix manifold. On nearly all modern jetliners, the airflow is approximately 50% outside air and 50% filtered air. Modern jetliners use high-efficiency particulate arresting HEPA filters, which trap more than 99% of all bacteria and clustered viruses . Air from

2457-482: The cabin. The aircraft instead draws air from dedicated inlets, located ahead of the wings. The primary component for the functioning of the cold air unit (CAU) is the Air Cycle Machine (ACM) cooling device. Some aircraft, including early Boeing 707 aircraft, used vapor-compression refrigeration like that used in home air conditioners . An ACM uses no Freon : the air itself is the refrigerant . The ACM

2520-480: The desired temperature, the bleed-air is passed through a heat exchanger called a pre-cooler . Air bled from the engine fan is blown across the pre-cooler, located in the engine strut , and absorbs excess heat from the service bleed air. A fan air modulating valve (FAMV) varies the cooling airflow to control the final air temperature of the service bleed air. Notably, the Boeing 787 does not use bleed air to pressurize

2583-400: The effectiveness and state of repair of air filtering systems, since they think that much of the air in an airplane cabin is recirculated. Almost all of the air in a pressurized aircraft is, in fact, brought in from the outside, circulated through the cabin and then exhausted through outflow valves in the rear of the aircraft. About 40 percent of the cabin's air goes through a HEPA filter and

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2646-437: The engine except during a compressor stall (essentially a jet engine backfire), thus the bleed air should be free of combustion contaminants from the normal running of the aircraft's own engines. However, on occasions carbon seals can leak oil (containing potentially hazardous chemicals) into the bleed air, in what is known in the industry as a fume event . This is generally dealt with quickly since failed oil seals will reduce

2709-420: The engine life. Oil contamination from this and other sources within the engine bay has led to health concerns from some advocacy groups and has triggered research by several academic institutions and regulatory agencies. However, no credible research has yielded evidence for the existence of a medical condition caused by fume events. Boeing Commercial Airplanes Boeing Commercial Airplanes ( BCA )

2772-441: The filter-media properties), HEPA filters experience the most difficulty in capturing particles in the size range of 0.15 to 0.2 μm. HEPA filtration works by mechanical means, unlike ionic and ozone treatment technologies, which use negative ions and ozone gas respectively. So, the likelihood of potential triggering of pulmonary side-effects such as asthma and allergies is much lower with HEPA purifiers. To ensure that

2835-510: The flow control valve (FCV). One FCV is installed for each PACK. A normally closed isolation valve prevents air from the left bleed system from reaching the right PACK (and vice versa ), although this valve may be opened in the event of loss of one bleed system. Downstream of the FCV is the cold-air unit (CAU), also referred to as the refrigeration unit. There are many various types of CAUs; however, they all use typical fundamentals. The bleed air enters

2898-445: The fuselage from over- and under- pressurization. Aircraft cabin pressure is commonly pressurized to a cabin altitude of 8000 feet or less. That means that the pressure is 10.9 pounds per square inch (75 kPa), which is the ambient pressure at 8,000 feet (2,400 m). Note that a lower cabin altitude is a higher pressure. The cabin pressure is controlled by a cabin pressure schedule, which associates each aircraft altitude with

2961-502: The live bacteria and viruses trapped by the filter media. Some of the best-rated HEPA units have an efficiency rating of 99.995%, which assures a very high level of protection against airborne disease transmission . Many vacuum cleaners also use HEPA filters as part of their filtration systems. This is beneficial for asthma and allergy sufferers, because the HEPA filter traps the fine particles (such as pollen and house dust mite feces ) which trigger allergy and asthma symptoms. For

3024-583: The load on the engines from bleed-air demands must be minimized. Airflow into the fuselage is approximately constant, and pressure is maintained by varying the opening of the out-flow valve (OFV). Most modern jetliners have a single OFV located near the bottom aft end of the fuselage, although some larger aircraft like the Boeing 747 and 777 have two. In the event the OFV should fail closed, at least two positive pressure relief valves (PPRV) and at least one negative pressure relief valve (NPRV) are provided to protect

3087-731: The low humidity causes drying of the skin, eyes and mucosal membranes and contributes to dehydration , leading to fatigue, discomfort and health issues. In one study the majority of flight attendants reported discomfort and health issues from low humidity. In a statement to US Congress in 2003 a member of the Committee on Air Quality in Passenger Cabins of Commercial Aircraft said "low relative humidity might cause some temporary discomfort (e.g., drying eyes, nasal passages, and skin), but other possible short- or long-term effects have not been established". A cabin humidity control system may be added to

3150-449: The manufacturing of hard disk drives, medical devices, semiconductors, nuclear, food and pharmaceutical products, as well as in hospitals, homes, and vehicles. HEPA filters are composed of a mat of randomly arranged fibers . The fibers are typically composed of polypropylene or fiberglass with diameters between 0.5 and 2.0 micrometers. Most of the time, these filters are composed of tangled bundles of fine fibers . These fibers create

3213-511: The mix manifold is directed to overhead distribution nozzles in the various zones of the aircraft. Temperature in each zone may be adjusted by adding small amounts of trim air, which is low-pressure, high-temperature air tapped off the AC PACK upstream of the TCV. Air is also supplied to individual gasper vents. A revolving control on the vent can be turned to adjust ventilation between no air output at all and

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3276-518: The model name as a suffix, including "ER" to designate an "extended range" version, such as the 777-300ER , or "LR" to designate a "long range" version, for example 777-200LR . Other suffix designators include "F" for "freighter" ( 747-400F ), "C" for "convertible" aircraft that can be converted between a passenger and freighter configuration ( 727-100C ), "SR" or "D" for "short range" and "domestic" ( 747-400D , 747SR ), and "M" for "combi" aircraft that are configured to carry both passengers and freight at

3339-466: The moisture to be flung through a sieve and toward the outer walls where it is channeled toward a drain and sent overboard. Then, the air usually will pass through a water separator coalescer or the sock. The sock retains the dirt and oil from the engine bleed air to keep the cabin air cleaner. This water removal process prevents ice from forming and clogging the system, and keeps the cockpit and cabin from fogging on ground operation and low altitudes. For

3402-559: The other 60 percent comes from outside the plane. Certified air filters block and capture 99.97 percent of airborne particles. In 2016, it was announced that the Tesla Model X would have the world's first HEPA-grade filter in a Tesla car. Following the release of the Model X, Tesla has updated the Model S to also have an optional HEPA air filter. The idea behind the development of the HEPA filter

3465-412: The primary ram-air heat exchanger, where it is cooled by either ram air, expansion or a combination of both. The cold air then enters the compressor, where it is repressurized, which reheats the air. A pass through the secondary ram-air heat exchanger cools the air while maintaining the high pressure. The air then passes through a turbine which expands the air to further reduce heat. Similar in operation to

3528-465: The same time ( 757-200M , 747-400M ). Passenger aircraft that are originally manufactured as passenger aircraft and later converted to freighter configuration by Boeing carry the suffix "BCF" designating a Boeing converted freighter ( 747-400BCF ). The table below lists only airliners from the jet era. Data from Boeing through April 2023 Airlines commonly order aircraft with special features or options, but Boeing builds certain models specifically for

3591-448: The spread of airborne radioactive contaminants. The US Army Chemical Corps and National Defense Research Committee needed to develop a filter suitable for removing radioactive materials from the air. The Army Chemical Corps asked Nobel Laureate Irving Langmuir to recommend filter test methods and other general recommendations for creating the material to filter out these radioactive particles. He identified 0.3 micron size particles to be

3654-410: The transition to 42 CFR 84 in 1995, use of the term HEPA has been deprecated except for powered air-purifying respirators . Some companies use the marketing term "True HEPA" to give consumers assurance that their air filters meet the HEPA standard, although this term has no legal or scientific meaning. Products that are marketed to be "HEPA-type," "HEPA-like," "HEPA-style" or "99% HEPA" do not satisfy

3717-530: The use of an activated carbon (charcoal) or other type of filter instead of or in addition to a HEPA filter. Carbon cloth filters, claimed to be many times more efficient than the granular activated carbon form at adsorption of gaseous pollutants , are known as high efficiency gas adsorption filters (HEGA) and were originally developed by the British Armed Forces as a defense against chemical warfare . A HEPA bag filter can be used in conjunction with

3780-418: The volume flow rate (m /s) divided by the face area (m ). The air space between HEPA filter fibers is typically much greater than 0.3 μm. HEPA filters in very high level for smallest particulate matter. Unlike sieves or membrane filters , where particles smaller than openings or pores can pass through, HEPA filters are designed to target a range of particle sizes. These particles are trapped (they stick to

3843-508: Was born from gas masks worn by soldiers fighting in World War II. A piece of paper found inserted into a German gas mask had a remarkably high capture efficiency for chemical smoke. The British Army Chemical Corps duplicated this and began to manufacture it in large quantities for their own service gas masks. They needed another solution for operational headquarters, where individual gas masks were impractical. The Army Chemical Corps developed

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3906-579: Was eventually ousted by Boeing in October 2019, in the midst of a company crisis following two fatal crashes of its 737 MAX jets. Stan Deal succeeded him in both of his positions. One insider called McAllister a "scapegoat" as he had only joined BCA during the later stages of the 737 MAX's development. In March 2024, Deal was in turn replaced by Stephanie Pope, formerly head of the Boeing Global Services division. For all models sold beginning with

3969-536: Was succeeded by Kevin G. McAllister , who was the first outside recruitment in BCA history. McAllister was instructed by Dennis Muilenburg to triple revenue from aftermarket services from $ 15 billion to a target of $ 50 billion over 10 years, with a new purpose-built unit headed by Stan Deal. Keith Leverkuhn was the vice president and general manager of the 737 MAX program in March 2017 when it received certification. McAllister

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