| Altitude |
| Aircraft Altitude |
| Cabin pressurization |
| Communication Tutorial |
|
Feet to Miles 60000ft= 11mi 640.0000yd Feet to Kilometers 60000ft= 18.28800km  “Why Do Planes Fly So High?” A cruising altitude refers to the altitude at which the aircraft shall spend most of its flight. This is exactly the altitude where the plane shall level out after taking off. Not only does this altitude allow the plane to fly more efficiently but it also prevents the chances of meeting other aircraft in the air. Although airplanes cruise at a wide range of levels and there are several factors that determine the cruising altitude of a plane. Cruising altitude for different airlines may vary between 25,000 feet and 40,000 feet. It is also not uncommon for an aircraft to change cruising altitude several times if it is a long journey flight. Every flight has a certain optimum cruising altitude which would depend on the weight of the aircraft. Here below are the factors and reasons why the aircraft has to travel high up in the air: • The air in the earth’s atmosphere becomes thinner as the altitude increases. When the air becomes thinner, it offers less resistance to objects flying through; this is why less thrust is required to move the aircraft. This in turn, helps the aircraft fly more efficiently. • Altitudes are defined in relation to number of feet above sea level. Pilots need to aware of the terrain over which they are flying. For example, twenty thousand feet may be suitable for southern Florida but it may not be the same if the aircraft was flying over mountains. • Cruising altitude would also depend on weather. Pilots receive weather reports and request alternate cruising altitude from air traffic control to avoid air turbulence. • The length of the flight also plays an important role. The cruising altitudes for short flights are usually less as compared to the cruising altitude for longer flights. • Flying too close to the clouds may make it hard for the pilot to see and cross winds may lead to air turbulence. • Flying low means more bug and insects on the wind shield which again can make it hard for the pilot to see in front and reduce visibility. • There is less friction at higher altitudes, less friction and higher air speed causes engines to burn less fuel therefore it improve fuel efficiency allowing the airplane to travel further. • Also, at higher altitudes, the air is less dense, therefore the aircraft can run more effectively • Best fuel efficiency occurs when the plane gets into the mid 30’s + • High altitude means less power is needed to propel the plane and at 40,000 feet the engines are just above idle power. These were just some reasons why aircrafts travel high up in the air. So you know now, that this is nothing to be worried about; good airlines take all safety measures to guarantee you have a safe and pleasurable trip. And even though you may be high up in the air, do not forget that the pilots operating the plane are experienced and know everything there is to be known in order to help you reach your destination at the earliest without any inconvenience. Enjoy your flight! What Is the Altitude of a Plane in Flight? When flying a plane, the pilot needs to know exactly how high above the earth the plane is traveling, a measurement that is called altitude. A pilot keeps track of altitude to ensure the plane is flying high enough to clear any topographical features that are below the flight path. Altitude is also monitored by air traffic controllers to ensure that the planes don’t pass too closely to each other while in flight. The Altimeter The pilot uses a gauge called an altimeter, which measures air pressure, to determine how high the plane is flying at any given time. The altimeter is shaped like a soup can with a dial on one end, and inside the “can” are a series of aneroid wafers, which act as a barometer, that expand or contract depending on the air pressure. As a plane climbs, the air becomes less dense, and the aneroids expand. When a plane loses altitude, or comes closer to the earth’s surface, the air pressure increases, and the aneroids contract. The movement of the aneroids is transferred to hands, like those on a clock, on the altimeter gauge. A separate knob allows the pilot to adjust the altimeter settings to reflect the terrain in the flight path. Controlling Altitude The pilot controls the altitude of the plane by using the yoke, the airplane’s equivalent of a steering wheel. The yoke controls the elevators, two horizontal wing-like pieces that are on the tail of the plane. If the pilot wants to decrease the altitude, he pushes the yoke forward and points the nose of the plane down, which causes the elevators to point down. To climb, the pilot pulls back on the yoke to bring the nose of the plane and the elevators up. If the pilot wants to hold a steady altitude, the yoke is held in a neutral position, causing the elevators to point straight back. Types of Altitude Altimeters are set to record the altitude based on how high a plane is flying above sea level, a measurement that is called "true" altitude. If the earth were round and smooth like a blown-up balloon, this is the only reading the pilot would need, but pilots must allow for flying over a landscape that ranges from low valleys to high mountain peaks. The measurement of a plane’s height over this variable surface is called "absolute" altitude. Pilots flying smaller aircraft usually have to calculate the difference between true and absolute altitude by using navigation charts. Larger planes, which typically can fly higher, use radar or radio altimeters to gauge altitude, or "radar" altitude. How High Planes Fly v Planes equipped with jet engines fly at greater altitudes than propeller-driven aircraft. These include commercial flights, cargo jets and even private passenger jets. The air traffic control tower usually assigns a cruising altitude of up to 39,000 feet, but long flights are typically assigned higher altitudes. By keeping these planes at assigned altitudes, air traffic control creates invisible stacked highways in the sky, keeping enough air space between the flights. Air traffic control may change an aircraft’s altitude assignment as needed. Most general aviation planes use propellers and must cruise at lower altitudes. For example, a Cessna Skyhawk has a maximum operating altitude of 13,500 feet. Planes that fly at higher altitudes must have pressurized cabins to keep the pilots and passengers safe and comfortable. The pressure and oxygen levels inside the cabin are set to correspond with those experienced at up to 7,000 feet. Cabin pressurization Cabin pressurization is a process in which conditioned air is pumped into the cabin of an aircraft or spacecraft, in order to create a safe and comfortable environment for passengers and crew flying at high altitudes. For aircraft, this air is usually bled off from the gas turbine engines at the compressor stage, and for spacecraft, it is carried in high-pressure, often cryogenic tanks. The air is cooled, humidified, and mixed with recirculated air if necessary, before it is distributed to the cabin by one or more environmental control systems.[1] The cabin pressure is regulated by the outflow valve. Need for cabin pressurization Pressurization becomes necessary at altitudes above 12,500 feet (3,800 m) to 14,000 feet (4,300 m) above sea level to protect crew and passengers from the risk of a number of physiological problems caused by the low outside air pressure above that altitude. It also serves to generally increase passenger comfort. The principal physiological problems are listed below. Pressurization of the cargo hold is also required to prevent damage to pressure-sensitive goods that might leak, expand, burst or be crushed on re-pressurization. Hypoxia The lower partial pressure of oxygen at altitude reduces the alveolar oxygen tension in the lungs and subsequently in the brain, leading to sluggish thinking, dimmed vision, loss of consciousness, and ultimately death. In some individuals, particularly those with heart or lung disease, symptoms may begin as low as 5,000 feet (1,500 m), although most passengers can tolerate altitudes of 8,000 feet (2,400 m) without ill effect. At this altitude, there is about 25% less oxygen than there is at sea level.[2]Hypoxia may be addressed by the administration of supplemental oxygen, either through an oxygen mask or through a nasal cannula. Without pressurization, sufficient oxygen can be delivered up to an altitude of about 40,000 feet (12,000 m). This is because a person who is used to living at sea level needs about 0.20 bar partial oxygen pressure to function normally and that pressure can be maintained up to about 40,000 feet (12,000 m) by increasing the mole fraction of oxygen in the air that is being breathed. At 40,000 feet (12,000 m), the ambient air pressure falls to about 0.2 bar, at which maintaining a minimum partial pressure of oxygen of 0.2 bar requires breathing 100% oxygen using an oxygen mask.Emergency oxygen supply masks in the passenger compartment of airliners do not need to be pressure-demand masks because most flights stay below 40,000 feet (12,000 m). Above that altitude the partial pressure of oxygen will fall below 0.2 bar even at 100% oxygen and some degree of cabin pressurization or rapid descent will be essential to avoid the risk of hypoxia. Altitude sickness Hyperventilation, the body’s most common response to hypoxia, does help to partially restore the partial pressure of oxygen in the blood, but it also causes carbon dioxide (CO2) to out-gas, raising the blood pH and inducing alkalosis. Passengers may experience fatigue, nausea, headaches, sleeplessness, and (on extended flights) even pulmonary oedema. These are the same symptoms that mountain climbers experience, but the limited duration of powered flight makes the development of pulmonary oedema unlikely. Altitude sickness may be controlled by a full pressure suit with helmet and faceplate, which completely envelops the body in a pressurized environment; however, this is impractical for commercial passengers. Decompression sickness The low partial pressure of gases, principally nitrogen (N2) but including all other gases, may cause dissolved gases in the bloodstream to precipitate out, resulting in gas embolism, or bubbles in the bloodstream. The mechanism is the same as that of compressed-air divers on ascent from depth. Symptoms may include the early symptoms of "the bends"—tiredness, forgetfulness, headache, stroke, thrombosis, and subcutaneous itching—but rarely the full symptoms thereof. Decompression sickness may also be controlled by a full-pressure suit as for altitude sickness. Barotrauma As the aircraft climbs or descends, passengers may experience discomfort or acute pain as gases trapped within their bodies expand or contract. The most common problems occur with air trapped in the middle ear (aerotitus) or paranasal sinuses by a blocked Eustachian tube or sinuses. Pain may also be experienced in the gastrointestinal tract or even the teeth (barodontalgia). Usually these are not severe enough to cause actual trauma but can result in soreness in the ear that persists after the flight and can exacerbate or precipitate pre-existing medical conditions, such as pneumothorax. Cabin altitude The pressure inside the cabin is technically referred to as the equivalent effective cabin altitude or more commonly as the cabin altitude. This is defined as the equivalent altitude above mean sea level having the same atmospheric pressure according to a standard atmospheric model such as the International Standard Atmosphere. Thus a cabin altitude of zero would have the pressure found at mean sea level, which is taken to be 101,325 pascals (14.696 psi).[3] Aircraft In practice, cabin altitude is almost never kept at zero due to design limits of the fuselage and practical considerations for landing at airports located above sea level.[citation needed] In a typical pressurization approach for a commercial passenger plane, the cabin altitude of an aircraft planning to cruise at 40,000 ft (12,000 m) is programmed to rise gradually from the altitude of the airport of origin to around a maximum of 8,000 ft (2,400 m) (approximately 10.9 psi, or 0.75 atm), and to then reduce gently during descent until the interior cabin pressure matches the ambient air pressure of the destination. A typical cabin altitude for an aircraft such as the Boeing 767 is 6,900 feet (2,100 m), when cruising at 39,000 feet (12,000 m).[4] A design goal for many, but not all, newer aircraft is to lower the cabin altitude, which can be beneficial for passenger comfort.[5] For example, the highest internal cabin altitude of the Boeing 787 Dreamliner is 6,000 feet (1,800 m). The Bombardier Global Express business jet has one of the lowest cabin altitudes of currently flying aircraft; 4,500 ft (1,400 m) when cruising at 41,000 feet (12,000 m).[6][7][8] The Airbus A380 has a cabin altitude of 4,990 feet (1,520 m), which is lower than that of the Boeing 747-400 (9,010 feet (2,750 m)).[9] The absolute lowest cabin altitude available on an aircraft is found on the Emivest SJ30 business jet which features a sea level cabin altitude when cruising at 41,000 feet (12,000 m). Keeping the cabin altitude below 8,000 ft (2,400 m) generally prevents significant hypoxia, altitude sickness, decompression sickness, and barotrauma.[citation needed] Federal Aviation Administration (FAA) regulations in the U.S. mandate that under normal operating conditions, the cabin altitude may not exceed this threshold at the maximum operating altitude of the aircraft.[citation needed] This mandatory maximum cabin altitude does not eliminate all physiological problems; passengers with conditions such as pneumothorax are advised not to fly until fully healed, and people suffering from a cold or other infection may still experience pain in the ears and sinuses.[citation needed] Scuba divers flying within the "no fly" period after a dive are at risk for decompression sickness because the accumulated nitrogen in their bodies can form bubbles when exposed to reduced cabin pressure.[ Before 1996, approximately 6,000 large commercial transport airplanes were type-certificated to fly up to 45,000 ft (14,000 m) without having to meet high-altitude special conditions.[12] In 1996, the FAA adopted Amendment 25-87, which imposed additional high-altitude cabin pressure specifications for new-type aircraft designs. Aircraft certified to operate above 25,000 ft (7,600 m) "must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of 15,000 ft (4,600 m) after any probable failure condition in the pressurization system".[13] In the event of a decompression which results from "any failure condition not shown to be extremely improbable", the plane must be designed such that occupants will not be exposed to a cabin altitude exceeding 25,000 ft (7,600 m) for more than 2 minutes, nor to an altitude exceeding 40,000 ft (12,000 m) at any time.[13] In practice, that new Federal Aviation Regulations amendment imposes an operational ceiling of 40,000 ft (12,000 m) on the majority of newly designed commercial aircraft.[14][15] Aircraft manufacturers can apply for a relaxation of this rule if the circumstances warrant it. In 2004, Airbus acquired an FAA exemption to allow the cabin altitude of the A380 to reach 43,000 ft (13,000 m) in the event of a decompression incident and to exceed 40,000 ft (12,000 m) for one minute. This allows the A380 to operate at a higher altitude than other newly designed civilian aircraft.[ Spacecraft Mechanics Pressurization is achieved by the design of an airtight fuselage engineered to be pressurized with a source of compressed air and controlled by an environmental control system (ECS). The most common source of compressed air for pressurization is bleed air extracted from the compressor stage of a gas turbine engine, from a low or intermediate stage and also from an additional high stage; the exact stage can vary depending on engine type. By the time the cold outside air has reached the bleed air valves, it is at a very high pressure and has been heated to around 200 °C (392 °F). The control and selection of high or low bleed sources is fully automatic and is governed by the needs of various pneumatic systems at various stages of flight.[ The part of the bleed air that is directed to the ECS is then expanded and cooled to a suitable temperature by passing it through a heat exchanger and air cycle machine known as the packs system. In some larger airliners, hot trim air can be added downstream of air conditioned air coming from the packs if it is needed to warm a section of the cabin that is colder than others. At least two engines provide compressed bleed air for all the plane's pneumatic systems, to provide full redundancy. Compressed air is also obtained from the auxiliary power unit (APU), if fitted, in the event of an emergency and for cabin air supply on the ground before the main engines are started. Most modern commercial aircraft today have fully redundant, duplicated electronic controllers for maintaining pressurization along with a manual back-up control system. All exhaust air is dumped to atmosphere via an outflow valve, usually at the rear of the fuselage. This valve controls the cabin pressure and also acts as a safety relief valve, in addition to other safety relief valves. If the automatic pressure controllers fail, the pilot can manually control the cabin pressure valve, according to the backup emergency procedure checklist. The automatic controller normally maintains the proper cabin pressure altitude by constantly adjusting the outflow valve position so that the cabin altitude is as low as practical without exceeding the maximum pressure differential limit on the fuselage. The pressure differential varies between aircraft types, typical values are between 7.8 psi (54 kPa) and 9.4 psi (65 kPa).[24] At 39,000 feet (12,000 m), the cabin pressure would be automatically maintained at about 6,900 feet (2,100 m) (450 feet (140 m) lower than Mexico City), which is about 11.5 psi (79 kPa) of atmosphere pressure.[ Some aircraft, such as the Boeing 787 Dreamliner, have re-introduced electric compressors previously used on piston-engined airliners to provide pressurization.[25] The use of electric compressors increases the electrical generation load on the engines and introduces a number of stages of energy transfer, therefore it is unclear whether this increases the overall efficiency of the aircraft air handling system. It does, however, remove the danger of chemical contamination of the cabin, simplify engine design, avert the need to run high pressure pipework around the aircraft, and provide greater design flexibility. Unplanned decompression Unplanned loss of cabin pressure at altitude is rare but has resulted in a number of fatal accidents. Failures range from sudden, catastrophic loss of airframe integrity (explosive decompression) to slow leaks or equipment malfunctions that allow cabin pressure to drop undetected to levels that can lead to unconsciousness or severe performance degradation of the aircrew. Any failure of cabin pressurization above 10,000 feet (3,000 m) requires an emergency descent to 8,000 feet (2,400 m) or the closest to that while maintaining terrain clearance (MSA), and the deployment of an oxygen mask for each seat. The oxygen systems have sufficient oxygen for all on board and give the pilots adequate time to descend to below 8,000 ft (2,400 m). Without emergency oxygen, hypoxia may lead to loss of consciousness and a subsequent loss of control of the aircraft. The time of useful consciousness varies according to altitude. As the pressure falls the cabin air temperature may also plummet to the ambient outside temperature with a danger of hypothermia or frostbite. In jet fighter aircraft, the small size of the cockpit means that any decompression will be very rapid and would not allow the pilot time to put on an oxygen mask. Therefore, fighter jet pilots and aircrew are required to wear oxygen masks at all times. On June 30, 1971, the crew of Soyuz 11, Soviet cosmonauts Georgy Dobrovolsky, Vladislav Volkov, and Viktor Patsayev were killed after the cabin vent valve accidentally opened before atmospheric re-entry. There had been no indication of trouble until the recovery team opened the capsule and found the dead crew.[ |