Landing

From Wikipedia, the free encyclopedia

For other uses, see Landing (disambiguation).

Landing is the last part of a flight, where a flying animal, aircraft, or spacecraft returns to the ground. When the flying object returns to water, the process is called alighting, although it is commonly called "landing" and "touchdown" as well.

Hitting the ground too hard is prevented by a wing (including rotor wings), a parachute or rockets or a vertically directed jet engine; in the case of a balloon the buoyancy is slightly decreased for a soft landing. Spacecraft or parts may have an airbag landing system.

Aircraft usually land at an airport on a firm runway or helicopter landing pad, generally constructed of asphalt concrete, concrete, gravel or grass, but specially equipped aircraft are able to land on water, snow or ice.

Image:Qantas b747 over houses arp.jpg

A landing Qantas Boeing 747-400 passes close to houses on the boundary of London Heathrow Airport, England

For aircraft or birds, landing is generally accomplished by gradually tapering down airspeed and lift. The first phase is the flare, where the rate of descent will be reduced by adopting a nose-up attitude. The attitude is held until the undercarriage touch the ground and the controls are either held until all wheels touch the ground or gently adjusted (often in the case of tail-draggers) to ensure the nose-wheel or tail-wheel lightly touches the runway.

In a small plane, with little crosswind, it is considered a "perfect" landing when contact with the ground occurs as the forward speed is reduced to the point where there is no longer sufficient airspeed to remain aloft. The stall warning is often heard just before landing indicating that this speed and altitude have been reached. The effect causes a very light touch down for the pilot and passengers.

Large transport category (airliner) aircraft land the aircraft by "flying the airplane on to the runway." The airspeed and attitude of the plane are adjusted for landing. The airspeed is kept well above stall speed and a constant rate of descent. Just before landing the descent rate is significantly reduced causing a light touch down. Usually spoilers (Sometimes called "Lift Dumpers") are immediately deployed to dramatically reduce the lift and transfer the aircraft's weight to its wheels, where mechanical braking can take effect. Reverse thrust is used by many jet aircraft to help slow down just after touch-down.

Image:Air.jamaica.a340-300.6y-jmp.arp.jpg

An airliner landing at London Heathrow Airport (Air Jamaica Airbus A340-300)

Factors such as crosswind where the pilot will use a crab landing or a slip landing will cause pilots to land slightly faster and sometimes with different attitudes to ensure proper handling and safety of the plane. Other factors effecting a particular landing might include some or all of the following partial list; the plane size, wind, weight, runway length, obstacles, ground effects, weather, runway altitude, air temperature, air pressure, air traffic control, visibility, avionics, and the overall situation, et cetera.

For example landing a multi-engine turboprop military (C-130 Hercules) under fire in a grass field in a warzone, requires different skills and precautions than landing a single engine plane (Cessna 150) on a paved runway in uncontrolled airspace, which is different from landing an airliner (Airbus A380) at a major airport with the support of air traffic control.

Pilots follow a course of training to develop the experience to routinely land in each situation. Professional pilots have extensive training, experience and certification on the types of planes they are flying.

Image:Mute.swan.touchdown.arp.jpg

A Mute Swan alighting. Note the ruffled feathers on top of the wings indicate that the swan is flying at the stalling speed. The extended and splayed feathers act as lift augmenters in the same way as an aircraft's slats and flaps.

To land on an aircraft carrier, the aircraft (moving at, perhaps, 150 mph [240 km/h]) is equipped with tailhooks to engage one of up to four arresting cables stretched across the deck, stopping the aircraft within 320 feet (100 m) after engaging one of the cables. To assist safe landings, the carrier will usually steam directly into wind at full speed, thus reducing aircraft's speed relative to the carrier deck, and eliminating any crosswind.

When a plane fails to land, it is called a crash.