The Airbus A330 is a medium- to long-range wide-body twin-engine jet airliner made by Airbus. Versions of the A330 have a range of 5,000 to 13,430 kilometres and can accommodate up to 335 passengers in a two-class layout or carry 70 tonnes of cargo; the A330's origin dates to the mid-1970s as one of several conceived derivatives of Airbus's first airliner, the A300. The A330 was developed in parallel with the four-engine A340, which shared many common airframe components but differed in number of engines. Both airliners incorporated fly-by-wire flight control technology, first introduced on an Airbus aircraft with the A320, as well as the A320's six-display glass cockpit. In June 1987, after receiving orders from various customers, Airbus launched the A330 and A340; the A330 was Airbus's first airliner that offered a choice of three engine types: General Electric CF6, Pratt & Whitney PW4000, Rolls-Royce Trent 700. The A330-300, the first variant, took its maiden flight in November 1992 and entered passenger service with Air Inter in January 1994.
Airbus followed up with the shorter A330-200 variant in 1998. Subsequently-developed A330 variants include a dedicated freighter, the A330-200F, a military tanker, the A330 MRTT, a corporate jet, ACJ330; the A330 MRTT formed the basis of the proposed KC-45, entered into the US Air Force's KC-X competition with Northrop Grumman, where after an initial win, on appeal lost to Boeing's tanker. Since its launch, the A330 has allowed Airbus to expand market share in wide-body airliners. Competing twinjets include the Boeing 767 and 777, along with the 787; the long-range Airbus A350 XWB was planned to succeed both the A330 and A340. Airbus intends to replace the current A330 with the A330neo, which includes new engines and other improvements; as of February 2019, A330 orders stand at 1,734, of which 1,441 have been delivered and 1,405 remain in operation. The largest operator is Turkish Airlines with 66 A330s in its fleet. Airbus's first airliner, the A300, was envisioned as part of a diverse family of commercial aircraft.
Pursuing this goal, studies began in the early 1970s into derivatives of the A300. Before introducing the A300, Airbus identified nine possible variations designated B1 through B9. A tenth variant, the A300B10, was conceived in 1973 and developed into the longer range Airbus A310. Airbus focused its efforts on single-aisle studies, conceiving a family of airliners known as the Airbus A320 family, the first commercial aircraft with digital fly-by-wire controls. During these studies Airbus turned its focus back to the wide-body aircraft market working on both projects. In the mid-1970s, Airbus began development of the A300B9, a larger derivative of the A300, which would become the A330; the B9 was a lengthened A300 with the same wing, coupled with the most powerful turbofan engines available. It was targeted at the growing demand for high-capacity, medium-range, transcontinental trunk routes. Offering the same range and payload as the McDonnell Douglas DC-10 but with 25 per cent more fuel efficiency, the B9 was seen as a viable replacement for the DC-10 and the Lockheed L-1011 TriStar trijets.
It was considered as a medium-ranged successor to the A300. At the same time, a 200-seat four-engine version, the B11 was under development; the B11 was planned to take the place of narrow-body Boeing 707s and Douglas DC-8s in commercial use, but would evolve to target the long-range, wide-body trijet replacement market. To differentiate from the SA series, the B9 and B11 were re-designated as the TA9 and TA11, with TA standing for "twin aisle". Development costs were reduced by the two aircraft using the same fuselage and wing, with projected savings of US$500 million. Another factor was the split preference of those within Airbus and, more those of prospective customers. Airbus found that most potential customers favoured four engines due to their exemption from existing twinjet range restrictions and their ability to be ferried with one inactive engine; as a result, development plans prioritised the four-engined TA11 ahead of the TA9. The first specifications for the TA9 and TA11, aircraft that could accommodate 410 passengers in a one-class layout, emerged in 1982.
They showed a large underfloor cargo area that could hold five cargo pallets or sixteen LD3 cargo containers in the forward, four pallets or fourteen LD3s in the aft hold—double the capacity of the Lockheed L-1011 TriStar or DC-10, 8.46 metres longer than the Airbus A300. By June 1985, the TA9 and TA11 had received more improvements, including the adoption of the A320 flight deck, digital fly-by-wire control system, side-stick control. Airbus had developed a common cockpit for their aircraft models to allow quick transition by pilots; the flight crews could transition from one type to another after only one week's training, which reduces operator costs. The two TAs would use the vertical stabiliser and circular fuselage sections of the A300-600, extended by two barrel sections. Airbus considered the variable camber wing, a concept that requires changing the wing profile for a given phase of flight. Studies were carried out at Hatfield and Bristol. Airbus estimated this would yield a two per cent improvement in aerodynamic efficiency, but the feature was rejected because of cost and difficulty of development.
A true laminar flow wing was conside
Ice is water frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color. In the Solar System, ice is abundant and occurs from as close to the Sun as Mercury to as far away as the Oort cloud objects. Beyond the Solar System, it occurs as interstellar ice, it is abundant on Earth's surface – in the polar regions and above the snow line – and, as a common form of precipitation and deposition, plays a key role in Earth's water cycle and climate. It occurs as frost, icicles or ice spikes. Ice molecules can exhibit more different phases that depend on temperature and pressure; when water is cooled up to three different types of amorphous ice can form depending on the history of its pressure and temperature. When cooled correlated proton tunneling occurs below −253.15 °C giving rise to macroscopic quantum phenomena. All the ice on Earth's surface and in its atmosphere is of a hexagonal crystalline structure denoted as ice Ih with minute traces of cubic ice denoted as ice Ic.
The most common phase transition to ice Ih occurs when liquid water is cooled below 0 °C at standard atmospheric pressure. It may be deposited directly by water vapor, as happens in the formation of frost; the transition from ice to water is melting and from ice directly to water vapor is sublimation. Ice is used in a variety including cooling, winter sports and ice sculpture; as a occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. It possesses a regular crystalline structure based on the molecule of water, which consists of a single oxygen atom covalently bonded to two hydrogen atoms, or H–O–H. However, many of the physical properties of water and ice are controlled by the formation of hydrogen bonds between adjacent oxygen and hydrogen atoms. An unusual property of ice frozen at atmospheric pressure is that the solid is 8.3% less dense than liquid water. The density of ice is 0.9167–0.9168 g/cm3 at 0 °C and standard atmospheric pressure, whereas water has a density of 0.9998–0.999863 g/cm3 at the same temperature and pressure.
Liquid water is densest 1.00 g/cm3, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. Density of ice increases with decreasing temperature and has a value of 0.9340 g/cm3 at −180 °C. When water freezes, it increases in volume; the effect of expansion during freezing can be dramatic, ice expansion is a basic cause of freeze-thaw weathering of rock in nature and damage to building foundations and roadways from frost heaving. It is a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes; the result of this process is that ice floats on liquid water, an important feature in Earth's biosphere. It has been argued that without this property, natural bodies of water would freeze, in some cases permanently, from the bottom up, resulting in a loss of bottom-dependent animal and plant life in fresh and sea water.
Sufficiently thin ice sheets allow light to pass through while protecting the underside from short-term weather extremes such as wind chill. This creates a sheltered environment for algal colonies; when sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae and annelids, which in turn provide food for animals such as krill and specialised fish like the bald notothen, fed upon in turn by larger animals such as emperor penguins and minke whales. When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C. During the melting process, the temperature remains constant at 0 °C. While melting, any energy added breaks the hydrogen bonds between ice molecules. Energy becomes available to increase the thermal energy only after enough hydrogen bonds are broken that the ice can be considered liquid water; the amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion.
As with water, ice absorbs light at the red end of the spectrum preferentially as the result of an overtone of an oxygen–hydrogen bond stretch. Compared with water, this absorption is shifted toward lower energies. Thus, ice appears blue, with a greener tint than liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice. Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. For instance, icebergs containing impurities can appear grey or green. Ice may be any one of the 18 known solid crystalline phases of water, or in an amorphous solid state at various densities. Most liquids under increased pressure freeze at higher temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: For some pressures higher than 1 atm, water freezes at a temperature below
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, sleet, snow and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates", thus and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate. Two processes acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called "showers."Moisture, lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain. This process is active when freezing rain occurs. A stationary front is present near the area of freezing rain and serves as the foci for forcing and rising air.
Provided necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely stratus and cumulonimbus. The cloud droplets will grow large enough to form raindrops and descend toward the Earth where they will freeze on contact with exposed objects. Where warm water bodies are present, for example due to water evaporation from lakes, lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extratropical cyclones. Lake-effect snowfall can be locally heavy. Thundersnow is possible within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation. On the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. Most precipitation is caused by convection; the movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes.
Precipitation is a major component of the water cycle, is responsible for depositing the fresh water on the planet. 505,000 cubic kilometres of water falls as precipitation each year. Given the Earth's surface area, that means the globally averaged annual precipitation is 990 millimetres, but over land it is only 715 millimetres. Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Precipitation may occur on other celestial bodies, e.g. when it gets cold, Mars has precipitation which most takes the form of frost, rather than rain or snow. Precipitation is a major component of the water cycle, is responsible for depositing most of the fresh water on the planet. 505,000 km3 of water falls as precipitation each year, 398,000 km3 of it over the oceans. Given the Earth's surface area, that means the globally averaged annual precipitation is 990 millimetres. Mechanisms of producing precipitation include convective and orographic rainfall.
Convective processes involve strong vertical motions that can cause the overturning of the atmosphere in that location within an hour and cause heavy precipitation, while stratiform processes involve weaker upward motions and less intense precipitation. Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice. Mixtures of different types of precipitation, including types in different categories, can fall simultaneously. Liquid forms of precipitation include drizzle. Rain or drizzle that freezes on contact within a subfreezing air mass is called "freezing rain" or "freezing drizzle". Frozen forms of precipitation include snow, ice needles, ice pellets and graupel; the dew point is the temperature to which a parcel must be cooled in order to become saturated, condenses to water. Water vapor begins to condense on condensation nuclei such as dust and salt in order to form clouds. An elevated portion of a frontal zone forces broad areas of lift, which form clouds decks such as altostratus or cirrostratus.
Stratus is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass. It can form due to the lifting of advection fog during breezy conditions. There are four main mechanisms for cooling the air to its dew point: adiabatic cooling, conductive cooling, radiational cooling, evaporative cooling. Adiabatic cooling occurs when air expands; the air can rise due to convection, large-scale atmospheric motions, or a physical barrier such as a mountain. Conductive cooling occurs when the air comes into contact with a colder surface by being blown from one surface to another, for example from a liquid water surface to colder land. Radiational cooling occurs due to the emission of infrared radiation, either by the air or by the surface underneath. Evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its wet-bulb temperature, or until it reaches saturation; the main ways water vapor is added to the air are: wind convergence into areas of upward motion, precipitation or virga falling from above, daytime heating evaporating water from the surface of oceans, water bodies or wet lan
A snowplow is a device intended for mounting on a vehicle, used for removing snow and ice from outdoor surfaces those serving transportation purposes. Although this term is used to refer to vehicles mounting such devices, more they are known as winter service vehicles in areas that receive large amounts of snow every year, or in specific environments such as airfields. In other cases, pickup trucks and front end loaders are outfitted with attachments to fulfill this purpose; some regions that do not see snow may use graders to remove compacted snow and ice off the streets. Snowplows can be mounted on rail cars or locomotives to clear railway tracks. A snowplow works by using a blade to push snow to the side to clear it from a surface. Modern plows may include technology to make it easier to stay on the road; these include head-up displays and infrared cameras. Large custom snowplows are used at major airports in North America; these plows have oversized blades and additional equipment like a rotating sweeper broom and blowers at the rear of the plow.
For sidewalks and narrow lanes small tractor plows are used within Canada and the United States. When snowfall accumulates above a certain height, snowplow operators may be seen clearing the main arteries first, in some cases for the exclusive use of emergency vehicles. Underbody scrapers are sometimes mounted on vehicles in residential and urban settings, operating on principles similar to a road grader, but allowing greater weights and speed along with the carriage of a road treatment applicator. Newer technology has allowed the use of articulated plow systems which can clear multiple divided highway lanes simultaneously; the first snow plows were horse-drawn wedge-plows made of wood. With the advent of the automobile, a number of inventors set about to improve existing snow plows. In the US, the "snow-clearer" is said to have been patented as early for railways; the first snow plow built for use with motor equipment was in 1913. It was manufactured by Good Roads Machinery in Kennett Square, PA. and was designed to meet the exacting requirements outlined by engineers of the New York City Street Cleaning Bureau.
Good Roads is therefore unofficially credited as the originator of the modern snow plow, though their horse drawn steel blade road graders were used to clear roads of snow as early as the company's founding in 1878 under their original name American Road Machinery. Good Roads patented the first four-wheel grader in 1889 thus making it the first pull grading apparatus patented in the United States. Unlike most early snow plow manufacturers, Good Roads continues to manufacture snow removal equipment today under the name Good Roads Godwin, now located in Dunn, North Carolina. In the early 1920s Good Roads advertised in The American City magazine that "...three out of every four snow plows in use throughout the whole United States are Good Roads Champions." By the mid-1920s Good Roads was manufacturing snow plows of various shapes and sizes for use on a wide variety of motorized equipment. Other snow plow manufactures began to follow suit as motorized plows were proven more efficient than other methods of snow removal.
In 1923, the brothers Hans and Even Øveraasen of Norway constructed an early snowplow for use on cars. This proved to be the start of a tradition in snow-clearing equipment for roads and airports, as well as the foundation of the company Øveraasen Snow Removal Systems. Carl Frink of Clayton, New York, USA was an early manufacturer of automobile-mounted snowplows, his company, Frink Snowplows, now Frink-America, was founded by some accounts as early as 1920. Today snow plows are produced by numerous companies around the world and available for different kinds of vehicles such as service trucks, pickup trucks, SUVs and ATVs, they are installed using model specific or universal hardware and mount to the frame of the vehicle to ensure durable connection. There are manual and hydraulic operating snow plows. All necessary mounting hardware comes in set with a plow. Snow plow blades are available in various sizes depending on a vehicle type. Service trucks use a blade sized 96 in and more. Common blade size for pickup trucks and full size SUVs is 78–96 in.
Smaller ATV snow plow blades are 48–78 in wide. In many countries, railway locomotives have small snowplows permanently attached to their bogies, which serve as pilots. With others, the snowplow forms part of the obstacle deflector below the bufferbeam. Bolt-on versions exist, these attach to the bufferbeam or front coupler. However, larger snowplows exist, which tend to be conversions rather than purpose-built vehicles. Steam locomotive tenders, large diesel locomotive bogies and various freight vehicles have been used, with the snowplow body mounted on the original frames, they are one-ended, with conventional coupling equipment on the inner end. In Canada purpose built snowplow cars are in use in areas where there is a significant snow fall during winter periods; these cars were influenced by the Russell Plow from the United States
Aviation accidents and incidents
In aviation, an accident is defined by the Convention on International Civil Aviation Annex 13 as an occurrence associated with the operation of an aircraft, which takes place from the time any person boards the aircraft with the intention of flight until all such persons have disembarked, in which a) a person is fatally or injured, b) the aircraft sustains significant damage or structural failure, or c) the aircraft goes missing or becomes inaccessible. Annex 13 defines an incident as an occurrence, other than an accident, associated with the operation of an aircraft that affects or could affect the safety of operation. A hull loss occurs if an aircraft is destroyed, damaged beyond repair, lost, or becomes inaccessible; the first fatal aviation accident was the crash of a Rozière balloon near Wimereux, France, on June 15, 1785, killing the balloon's inventor, Jean-François Pilâtre de Rozier, the other occupant, Pierre Romain. The first involving a powered aircraft was the crash of a Wright Model A aircraft at Fort Myer, Virginia, in the United States on September 17, 1908, injuring its co-inventor and pilot, Orville Wright, killing the passenger, Signal Corps Lieutenant Thomas Selfridge.
2,996: The deadliest aviation-related disaster of any kind, considering fatalities on both the aircraft and the ground, was the destruction of the World Trade Center in New York City on September 11, 2001. On that morning, four commercial aircraft traveling on transcontinental flights from East Coast airports to California were hijacked after takeoff; the four hijacked aircraft were subsequently crashed in four separate suicide attacks against major American landmarks, by 19 Islamic terrorists affiliated with Al Qaeda. American Airlines Flight 11 and United Airlines Flight 175 were intentionally crashed into the North and South Towers of the World Trade Center, destroying both buildings in less than two hours; the World Trade Center crashes killed 2,753, the vast majority of fatalities being occupants of the World Trade Center towers or emergency personnel responding to the disaster. In addition, 184 were killed by American Airlines Flight 77. 40 passengers were killed when United Airlines Flight 93 crashed into a Somerset County Pennsylvania field after passengers fought back and prevented the hijackers from reaching their designated target.
This brought the total number of casualties of the September 11 attacks to 2,996. As deliberate terrorist acts, the 9/11 crashes were not classified as accidents, but as mass murder-suicide. 583: The Tenerife airport disaster, which occurred on March 27, 1977, remains the accident with the highest number of airliner passenger fatalities. 583 people died when a KLM Boeing 747 attempted to take off without flight clearance, collided with a taxiing Pan Am 747 at Los Rodeos Airport on the Canary Island of Tenerife, Spain. There were no survivors from the KLM aircraft and only 61 of the 396 passengers and crew on the Pan Am aircraft survived. Pilot error was the primary cause, as the KLM captain began his takeoff run without obtaining air traffic control clearance. A contributing factor was the dense fog; the KLM flight crew could not see the Pan Am aircraft on the runway until before the collision. The accident had a lasting influence on the industry in the area of communication. An increased emphasis was placed on using standardized phraseology in air traffic control communication by both controllers and pilots alike.
"Cockpit Resource Management" has been incorporated into flight crew training. The captain is no longer considered infallible, combined crew input is encouraged during aircraft operations. 520: The crash of Japan Airlines Flight 123 on August 12, 1985, is the single-aircraft disaster with the highest number of fatalities: 520 people died on board a Boeing 747. The aircraft suffered an explosive decompression from an incorrectly repaired aft pressure bulkhead, which failed in mid flight, destroying most of its vertical stabilizer and severing all of the hydraulic lines, making the 747 uncontrollable. Pilots were able to keep the plane flying for 32 minutes after the mechanical failure before crashing into a mountain. All 15 crew members and 505 of the 509 passengers on board died. Rescue operations were delayed until the following morning, which decreased the number of victims who would have survived the incident. Furthermore, Japanese personnel inaccurately assumed, during a helicopter flyover of the impact site, that there were no survivors.
Medical providers involved in rescue and analysis operations determined that several passengers survived the impact and would have survived the incident had rescue operations not been delayed. Four passengers survived the incident in its entirety. 349: On November 12, 1996, the world's deadliest mid-air collision was the Charkhi Dadri mid-air collision involving Saudia Flight 763 and Kazakhstan Airlines Flight 1907 over Charkhi Dadri, India. The collision was the result of the Kazakh pilot flying lower than the assigned clearance altitude. All 349 passengers and crew on board of both the aircraft died; the Ramesh Chandra Lahoti Commission, empowered to study the causes, recommended the creation of the "semi-circular rule", to prevent aircraft from flying in opposite directions at the same altitude. The Civil Aviation Authorities in India made it mandatory for all aircraft flying in and out of India to be equipped with a Traffic Collision Avoi
Snow refers to forms of ice crystals that precipitate from the atmosphere and undergo changes on the Earth's surface. It pertains to frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size and accumulate on surfaces metamorphose in place, melt, slide or sublimate away. Snowstorms develop by feeding on sources of atmospheric moisture and cold air. Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets, which freeze in hexagonal-shaped crystals. Snowflakes take on a variety of shapes, basic among these are platelets, needles and rime; as snow accumulates into a snowpack, it may blow into drifts. Over time, accumulated snow metamorphoses, by sintering and freeze-thaw. Where the climate is cold enough for year-to-year accumulation, a glacier may form. Otherwise, snow melts seasonally, causing runoff into streams and rivers and recharging groundwater. Major snow-prone areas include the polar regions, the upper half of the Northern Hemisphere and mountainous regions worldwide with sufficient moisture and cold temperatures.
In the Southern Hemisphere, snow is confined to mountainous areas, apart from Antarctica. Snow affects such human activities as transportation: creating the need for keeping roadways and windows clear. Snow affects ecosystems, as well, by providing an insulating layer during winter under which plants and animals are able to survive the cold. Snow develops in clouds; the physics of snow crystal development in clouds results from a complex set of variables that include moisture content and temperatures. The resulting shapes of the falling and fallen crystals can be classified into a number of basic shapes and combinations, thereof; some plate-like and stellar-shaped snowflakes can form under clear sky with a cold temperature inversion present. Snow clouds occur in the context of larger weather systems, the most important of, the low pressure area, which incorporate warm and cold fronts as part of their circulation. Two additional and locally productive sources of snow are lake-effect storms and elevation effects in mountains.
Mid-latitude cyclones are low pressure areas which are capable of producing anything from cloudiness and mild snow storms to heavy blizzards. During a hemisphere's fall and spring, the atmosphere over continents can be cold enough through the depth of the troposphere to cause snowfall. In the Northern Hemisphere, the northern side of the low pressure area produces the most snow. For the southern mid-latitudes, the side of a cyclone that produces the most snow is the southern side. A cold front, the leading edge of a cooler mass of air, can produce frontal snowsqualls—an intense frontal convective line, when temperature is near freezing at the surface; the strong convection that develops has enough moisture to produce whiteout conditions at places which line passes over as the wind causes intense blowing snow. This type of snowsquall lasts less than 30 minutes at any point along its path but the motion of the line can cover large distances. Frontal squalls may form a short distance ahead of the surface cold front or behind the cold front where there may be a deepening low pressure system or a series of trough lines which act similar to a traditional cold frontal passage.
In situations where squalls develop post-frontally it is not unusual to have two or three linear squall bands pass in rapid succession only separated by 25 miles with each passing the same point in 30 minutes apart. In cases where there is a large amount of vertical growth and mixing the squall may develop embedded cumulonimbus clouds resulting in lightning and thunder, dubbed thundersnow. A warm front can produce snow for a period, as warm, moist air overrides below-freezing air and creates precipitation at the boundary. Snow transitions to rain in the warm sector behind the front. Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water, warming the lower layer of air which picks up water vapor from the lake, rises up through the colder air above, freezes and is deposited on the leeward shores; the same effect occurs over bodies of salt water, when it is termed ocean-effect or bay-effect snow. The effect is enhanced when the moving air mass is uplifted by the orographic influence of higher elevations on the downwind shores.
This uplifting can produce narrow but intense bands of precipitation, which deposit at a rate of many inches of snow each hour resulting in a large amount of total snowfall. The areas affected by lake-effect snow are called snowbelts; these include areas east of the Great Lakes, the west coasts of northern Japan, the Kamchatka Peninsula in Russia, areas near the Great Salt Lake, Black Sea, Caspian Sea, Baltic Sea, parts of the northern Atlantic Ocean. Orographic or relief snowfall is caused when masses of air pushed by wind are forced up the side of elevated land formations, such as large mountains; the lifting of air up the side of a mountain or range results in adiabatic cooling, condensation and precipitation. Moisture is removed by orographic lift, leaving drier, warmer air on the leeward side; the resulting enhanced productivity of snow fall and the decrease in temperature with elevation means that snow depth
A taxiway is a path for aircraft at an airport connecting runways with aprons, hangars and other facilities. They have a hard surface such as asphalt or concrete, although smaller general aviation airports sometimes use gravel or grass. Busy airports construct high-speed or rapid-exit taxiways to allow aircraft to leave the runway at higher speeds; this allows the aircraft to vacate the runway quicker, permitting another to land or take off in a shorter interval of time. This is accomplished by making the exiting taxiway longer, thus giving the aircraft more space in which to slow down, before the taxiways' upcoming intersection with another taxiway, another runway, or the ramp/tarmac. Most airports do not have a specific speed limit for taxiing. There is a general rule on safe speed based on obstacles. Operators and aircraft manufacturers might have limits. Typical taxi speeds are 20-30 knots. Normal Centerline A single continuous yellow line, 15 centimetres to 30 centimetres in width. Enhanced Centerline The enhanced taxiway center line marking consists of a parallel line of yellow dashes on either side of the taxiway centerline.
Taxiway centerlines are enhanced for 150 feet before a runway holding position marking. The enhanced taxiway centerline is standard at all FAR Part 139 certified airports in the USA. Taxiway Edge Markings Used to define the edge of the taxiway when the edge does not correspond with the edge of the pavement. Continuous markings consist of a continuous double yellow line, with each line being at least 15 centimetres in width, spaced 15 centimetres apart, they divide the taxiway edge from the shoulder or some other abutting paved surface not intended for use by aircraft. Dashed markings define the edge of a taxiway on a paved surface where the adjoining pavement to the taxiway edge is intended for use by aircraft, e.g. an apron. These markings consist of a broken double yellow line, with each line being at least 15 centimetres in width, spaced 15 centimetres apart; these lines are 15 feet in length with 25 foot gaps. Taxi Shoulder Markings Taxiways, holding bays, aprons are sometimes provided with paved shoulders to prevent blast and water erosion.
Shoulders are not intended for use by aircraft, may be unable to carry the aircraft load. Taxiway shoulder markings are yellow lines perpendicular to the taxiway edge, from taxiway edge to pavement edge, about 3 metres. Surface Painted Taxiway Direction Signs Yellow background with a black inscription, provided when it is not possible to provide taxiway direction signs at intersections, or when necessary to supplement such signs; these markings are located on either side of the taxiway. Surface Painted Location Signs Black background with a yellow inscription and yellow and black border. Where necessary, these markings supplement location signs located alongside the taxiway and assist the pilot in confirming the designation of the taxiway on which the aircraft is located; these markings are located on the right side of the centerline. Geographic Position Markings, they are positioned to the left of the taxiway centerline in the direction of taxiing. Black inscription centered on pink circle with white outer ring.
If the pavement is a light colour the border is white with a black outer ring. Runway Holding Position Markings These show where an aircraft should stop when approaching a runway from a taxiway, they consist of four yellow lines, two solid and two dashed, spaced six or twelve inches apart, extending across the width of the taxiway or runway. The solid lines are always on the side. There are three locations where runway holding position markings are encountered: Runway holding position markings on taxiways. Holding Position Markings for Instrument Landing System These consist of two yellow solid lines spaced two feet apart connected by pairs of solid lines spaced ten feet apart extending across the width of the taxiway. Holding Position Markings for Taxiway/Taxiway Intersections These consist of a single dashed line extending across the width of the taxiway. Surface Painted Holding Position Signs Red background signs with a white inscription to supplement the signs located at the holding position.
The taxiways are given alphanumeric identification. These taxiway IDs are shown on yellow signboards along the taxiways. Airport guidance signs provide information to taxiing aircraft and airport vehicles. Smaller airports may have few or no signs, relying instead on airport charts. There are two classes of signage at airports, with several types of each: Location signs – yellow on black background. Identifies the runway or taxiway the aircraft is on or is entering. Direction/Runway exit signs – black on yellow. Identifies the intersecting taxiways the aircraft is approaching, with an arrow indicating the direction to turn. Stop Bar signs – white on blue background; the designation consists of the letter S followed by designation of the taxiway on which the Stop Bar is positioned. This sign is not standard. Other – many airports use conventional traffic signs such as stop and yield signs throughout the airport. Mandatory instruction signs are white on red, they show entrances to critical areas. Vehicles and aircraft are required to stop at these signs until the control tower gives clearance to proceed.
Runway signs – White text on a red background. These signs identify a runway inte