Pushback - AbsoluteAstronomy.com

Aviation

Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...

, pushback is an airport

Airport

An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...

procedure during which an aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

is pushed backwards away from an airport

Airport

An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...

gate

Gate (airport)

A gate in aviation is a long, movable, "bridge" that allows passengers to embark and disembark their aircraft.* Jetway bridges* Air stairs, either built into the aircraft or from a mobile vehicle* Mobile lounges...

by external power. Pushbacks are carried out by special, low-profile vehicles called pushback tractor
Tractor
A tractor is a vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction...

s or tugs.

Although many aircraft can also move backwards on the ground using reverse thrust (a procedure referred to as a powerback
Powerback
Powerback is used by aircraft to reverse using the power of their engines, In Europe only propeller aircraft tend to use powerbacks as a means of reversing, while in the USA some larger jet aircraft also perform powerbacks....

), the resulting jet blast

Jet engine

A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

or prop wash may cause damage to the terminal building or equipment. Engines close to the ground may also blow sand and debris forward and then suck it in to the engine, causing damage to the engine. A pushback using a tractor is therefore the preferred method to move the aircraft away from the gate.

Procedure

Pushbacks at busy aerodrome

Aerodrome

An aerodrome, airdrome or airfield is a term for any location from which aircraft flight operations take place, regardless of whether they involve cargo, passengers or neither...

s are usually subject to ground control

Air traffic control

Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...

clearance to facilitate ground movement on taxiway

Taxiway

A taxiway is a path on an airport connecting runways with ramps, hangars, terminals and other facilities. They mostly have hard surface such as asphalt or concrete, although smaller airports sometimes use gravel or grass....

s. Once clearance is obtained, the pilot will communicate with the pushback tractor driver (or a ground handler walking alongside the aircraft in some cases) to start the pushback. To communicate, a headset

Headphones

Headphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user's ears and connected to a signal source such as an audio amplifier, radio, CD player or portable Media Player. They are also known as stereophones, headsets or, colloquially, cans. The in-ear...

may be connected near the nose gear.

Since the pilots cannot see what is behind the aircraft, steering is done by the pushback tractor driver and not by the pilots. Depending on the aircraft type and airline procedure, a bypass pin may be temporarily installed into the nose gear to disconnect it from the aircraft's normal steering mechanism.

Once the pushback is completed, the towbar is disconnected, and the bypass pin is removed. The ground handler will show the bypass pin to the pilots to make it absolutely clear that it has been removed. The pushback is then complete, and the aircraft can start taxiing forward under its own power.

Equipment

Pushback tractors use a low profile design to fit under the aircraft nose. For sufficient traction

Traction (engineering)

Traction refers to the maximum frictional force that can be produced between surfaces without slipping.The units of traction are those of force, or if expressed as a coefficient of traction a ratio.-Traction:...

, the tractor must be heavy, and most models can have extra ballast added. A typical tractor for large aircraft weighs up to 54 t (119,049.6 lb) and has a drawbar

Drawbar (haulage)

A drawbar is a solid coupling between a hauling vehicle and its hauled load. Drawbars are in common use with rail transport, road trailers, both large and small, industrial and recreational, and with agricultural equipment.-Agriculture:...

pull of 334 kN (75,086.2 lbf). Often, the driver's cabin can be raised for increased visibility when reversing, and lowered to fit under aircraft.

Tractor types

There are two types of pushback tractors: conventional and towbarless (TBL).

Conventional tugs use tow bars to connect to the nose wheel of the aircraft. The tow bar can be connected at the front or the rear of the tractor, depending on whether the aircraft will be pushed or pulled.
The towbar has a shear pin

Shear pin

A shear pin is a safety device designed to shear in the case of a mechanical overload, preventing other, more-expensive parts from being damaged...

. The shear pin prevents the aircraft from being mishandled by the tug—when overstressed the shear pin will snap, disconnecting the bar from the nose gear to prevent damage to the aircraft and tug.

Towbarless tractors do not use a towbar. They scoop up the nose wheel and lift it off the ground, allowing the tug to manoeuvre the aircraft. This allows better control of the aircraft, higher speeds, without anyone in the cockpit. The main advantage of a towbarless tug is simplicity. By eliminating the towbar, operators are alleviated from maintaining many towbars. Also, the physical action and coordination required by the tug operator to move an aircraft with a TBL tug is simpler and easier to learn than with a towbar. By connecting the tug directly to the aircraft's landing gear - instead of through a towbar - tug operators have better control and responsiveness when maneuvering. This is most advantageous in general aviation settings, where operators are often required to move more aircraft (and a wider variety of aircraft) into smaller, more confined spaces than their airline counterparts.

Manufacturers of electric TBL tugs offer a line of models capable of moving any aircraft from the smallest single engine to narrow-body airliners, military cargo and airline-sized business jets. Just as specialized towbars are required for a wide range of aircraft, many TBL tugs use adapters which enable the movement of many unique aircraft. The majority of aircraft do not require adapters, and can be moved without any special adjustments to the tug. This is in contrast to conventional tugs, which often use so-called "universal" towbars that need to be adjusted for many aircraft types. Electric TBL tugs are gaining popularity among general aviation operators and FBOs as an alternative to gas-/diesel-powered, conventional tugs. Being electric- as opposed to internal combustion-powered, electric tugs are low-emission, a major advantage for environmentally-conscious operators. Also, this enables the tug to be safely operated inside a closed hangar.

Very small aircraft may be moved by human power alone. A short pushbar is attached to the nose gear to allow the aircraft to be steered without anyone at the aircraft controls.

Military versions

In general, the military pushback vehicles are equivalent to the civil ones. But sometimes the Military need very compact ones who can maneuver on limited areas. This is important on aircraft carriers and in confined spaces, such as aircraft caverns

Aircraft cavern

Aircraft cavern is the literal translation of the German word Flugzeugkaverne. A Flugzeugkaverne is an underground hangar used by the Swiss Air Force.-Design:...

or sometimes in Hardened Aircraft Shelters (HAS)

Hardened Aircraft Shelter

Hardened Aircraft Shelters , or Protective Aircraft Shelter , are a reinforced structure to house and protect military aircraft from enemy attack...

. Some military pushback tractors allow the driver to release the aircraft during the drive, which is useful for Quick Reaction Alert (QRA) out of the mountain caverns, as in the case of the Swiss Air Force

Swiss Air Force

The Swiss Air Force is the air component of the Swiss Armed Forces, established on July 31, 1914, as part of the Army and as of January 1966 an independent service.In peacetime, Dübendorf is the operational Air Force HQ...

Mirage IIIS

Dassault Mirage III

The Mirage III is a supersonic fighter aircraft designed by Dassault Aviation during the late 1950s, and manufactured both in France and a number of other countries. It was a successful fighter aircraft, being sold to many air forces around the world and remaining in production for over a decade...

. To prevent ignition these vehicles are powered by diesel engines (because of the limited fresh air circulation in mountain caverns and HAS the concentration of kerosene in the air can be higher as in a Shelter and the use of a gasoline motor could be dangerous). To tug out an aircraft in useful speed/time from a mountain cavern or HAS the tractors are equipped with a special light, often called visor. The driver has to follow with the beam of it at the markings that are painted on the ground. Because of the different size of the aircraft types there are different markings. Usually these military pushback tractors are able to supply fighters with electric power. Apart from towing jets and helicopters, they are also often used to tow mobile APUs, various weapons, as well as other equipment. The U.S. Navy uses the A/S32A-30-... aircraft ground support equipment

Ground Support Equipment

Ground support equipment is the support equipment found at an airport, usually on the ramp, the servicing area by the terminal. This equipment is used to service the aircraft between flights. As its name implies, GSE is there to support the operations of aircraft on the ground...

towing tractor, called "Spotting dolly"-

Other equipment applications

While the vehicle is referred to as a pushback tug, it is also used to tow aircraft in areas where taxiing the aircraft is not practical or unsafe, such as moving aircraft in and out of maintenance hangar

Hangar

A hangar is a closed structure to hold aircraft or spacecraft in protective storage. Most hangars are built of metal, but other materials such as wood and concrete are also sometimes used...

s, or moving aircraft that are not under their own power.

Some airlines, notably Virgin Atlantic, are now advocating towing aircraft to the holding point of the runway to save fuel and reduce environmental impact.

Incidents

Incidents or accidents involving a pushback include:

Garuda Indonesia
Garuda Indonesia
PT Garuda Indonesia Tbk , publicly known as Garuda Indonesia, is the flag carrier of Indonesia. It is named after the mystical giant bird Garuda of Hinduism and Buddhist mythology. It is headquartered at Soekarno-Hatta International Airport in Tangerang, near Jakarta, the capital city of Indonesia...

Boeing 737-500, operating as Flight 238, collided with a Saudi Arabian Airlines
Saudi Arabian Airlines
Saudi Arabian Airlines is the flag carrier airline of Saudi Arabia, based in Jeddah. It operates domestic and international scheduled flights to over 90 destinations in the Middle East, Africa, Asia, Europe and North America...

Boeing 747-300. No casualties or injuries.

In the media

In an advertising campaign, also documented on the television show Fifth Gear

Fifth Gear

Fifth Gear is a motoring television magazine show from the United Kingdom. Originally shown on Channel 5, the show is currently presented by Tiff Needell, Vicki Butler-Henderson, Jason Plato, Jonny Smith and Ben Collins...

, a Volkswagen Touareg

Volkswagen Touareg

The Volkswagen Touareg is a mid-size crossover SUV produced by German automaker Volkswagen since 2002. The vehicle was named after the Tuareg people, a Berber-speaking group in North Africa...

was used to pull a Boeing 747

Boeing 747

The Boeing 747 is a wide-body commercial airliner and cargo transport, often referred to by its original nickname, Jumbo Jet, or Queen of the Skies. It is among the world's most recognizable aircraft, and was the first wide-body ever produced...

. As cited before, the "tractor" needs to be heavy to aid traction. The Touareg carried 4.3 tons worth of cement bags, and the tires were inflated to twice the normal pressure to handle the extra weight. Tractor tires have high sidewall ratios for this reason. This is the world record for the heaviest load towed by a production car.