Pushback (aviation)

2023-10-04T22:58:11Z

106.64.161.157:

{{Short description|Removal of an aircraft from an airport gate by external power}}

[[File:KLM 777 pushback.jpg|thumb|A [[KLM]] [[Boeing 777]] being pushed back from a gate at [[Narita International Airport]] in Japan.]]
In [[aviation]], '''pushback''' is an [[airport]] procedure during which an [[aircraft]] is pushed backwards away from its parking position, usually at an airport [[Gate (airport)|gate]] by external power.<ref name=IATA/><ref name="Kumar">{{cite book |last1=Kumar |first1=Bharat |last2=DeRemer |first2=Dale |last3=Marshall |first3=Douglas M. |title=An Illustrated Dictionary of Aviation |publisher=McGraw-Hill |location=New York |isbn=978-0-07-139606-6 |page=514 |date=2004 |ref=Kumar}}</ref> Pushbacks are carried out by special, low-profile vehicles called ''pushback [[tractor]]s'' or ''tugs''.

Although many aircraft are capable of moving themselves backwards on the ground using [[reverse thrust]] (a procedure referred to as a ''[[powerback]]),''<ref name=IATA/> the resulting [[jet blast]] or [[prop wash]] would cause increased noise, damage to the terminal building or equipment, and can cause injury to airport staff due to flying debris. This debris would also be sucked into the engine, as it is in normal use, and cause excessive wear - a major cause of wear on aircraft engines is during ground use.<ref>{{Cite journal|last=Ravikovich|first=A|year=2020|title=Criterion for evaluation of erosion of aviation engine parts from polymer composite materials|url=https://www.researchgate.net/publication/342279060|journal=IOP Conf. Series: Materials Science and Engineering|volume=868|issue=1|pages=1|doi=10.1088/1757-899X/868/1/012026|bibcode=2020MS&E..868a2026R|quote=This effect is inherent in the take-off and landing stages when sand and dust are lifted from the runway by an air stream, which greatly affects the durability of PCM parts.|via=Research Gate|doi-access=free}}</ref> A pushback is therefore the preferred method when ground-handling aircraft.

==Definition==
[[International Air Transport Association|IATA]] defines aircraft pushback as "rearward moving of an aircraft from a parking position to a taxi position by use of specialized [[ground support equipment]]."<ref name="IATA">{{cite web |title=IATA Reference Manual (IRM) for Audit Programs 11th edition |url=https://www.iata.org/en/iata-repository/publications/iosa-audit-documentation/iata-reference-manual-for-audit-programs-irm--ed-102/ |website=IATA.org |publisher=International Air Transport Association |access-date=2 May 2021 |date=2021 |location=Montreal—Geneva |ref=IATA}}</ref>

==Procedure==
[[File:Airbus-A380-Pushback-001.ogv|thumb|[[Airbus A380]] pushback]]
Pushbacks at busy [[aerodrome]]s are usually subject to [[air traffic control|ground control]] clearance to facilitate ground movement on [[taxiway]]s.<ref name=Smith/><ref name="Doc4444">{{cite web |title=Doc 4444 Procedures for Air Navigation Services — Air Traffic Management (PANS-ATM) |date=2016 | url=https://ops.group/blog/wp-content/uploads/2017/03/ICAO-Doc4444-Pans-Atm-16thEdition-2016-OPSGROUP.pdf |website=OPS Group |access-date=2 May 2021 |ref=Doc4444 |page=12.3.4.4}}</ref> Once clearance is obtained, the pilot will communicate with the tractor driver (or a ground handler walking alongside the aircraft in some cases) to start the pushback. To communicate, a [[Headphones|headset]] 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 any bypass pin removed. The ground handler will show the bypass pin to the pilots to make it clear that it has been removed.<ref name="Smith">{{cite book |last1=Smith |first1=David |title=Air Traffic Control Handbook |publisher=Crécy |location=Manchester |isbn=978-08597-91830 |page=127 |edition=10th |date=2015 |ref=Smith}}</ref> The pushback is then complete, and the aircraft can taxi forward under its own power.

==Equipment==

=== Moving light aircraft ===
[[Image:aerotechnik.ev97a.eurostar.g-ccmp.arp.jpg|thumb|[[Light aircraft]] can usually be moved by human power alone. Here, this [[Evektor-Aerotechnik|Aerotechnik EV-97A Eurostar]] is being pulled into position for refueling]]

Very small airplanes may be moved by human power alone. The airplane may be pushed or pulled by [[landing gear]] or [[wing struts]] since they're known to be strong enough to drag the airplane through the air. To allow for turns, a person may either pick up or push down on the tail to raise either the nose wheel or [[tail wheel]] off the ground, then rotate the airplane by hand. A less cumbersome method involves attaching a short tow bar to either the nose wheel or tail wheel, which provides a solid handhold and leverage to steer with, as well as eliminates the danger of handling the propeller. These tow bars are usually a lightweight [[aluminum alloy]] construction which allows them to be carried on board the airplane. Other small tow bars have a powered wheel to help move the airplane, with power sources as diverse as lawnmower engines or battery-operated electric drills. However, powered tow bars are usually too large and heavy to be practically carried on small airplanes.
{{clear}}

===Tractors and towbars===
[[File:Pushback tug carrying a towbar.JPG|thumb|Pushback tug with a towbar on the apron]]

[[Image:Airplane pushing vehicle.jpg|thumb|A conventional tractor hooked up to a [[United Airlines]] [[Boeing 777-200ER]] at [[Denver International Airport]]]]
Large aircraft cannot be moved by hand and must have a tractor or tug. Pushback tractors use a low profile design to fit under the aircraft nose. For sufficient [[Traction (engineering)|traction]] the tractor must be heavy, and most models can have extra [[wiktionary:ballast|ballast]] added. A typical tractor for large aircraft weighs up to {{convert|54|t|ST LT lb|sigfig=3|abbr=off}} and has a [[Drawbar (haulage)|drawbar]] pull of {{convert|334|kN|lbf|abbr=on}}. Often the driver's cabin can be raised for increased visibility when reversing and lowered to fit under aircraft. There are two types of pushback tractors: conventional and towbarless (TBL).

Conventional tugs use a tow bar to connect the tug to the nose landing gear of the aircraft. The tow bar is fixed laterally at the nose landing gear, but may move slightly vertically for height adjustment. At the end that attaches to the tug, the tow bar may pivot freely laterally and vertically. In this manner the tow bar acts as a large lever to rotate the nose landing gear. Each aircraft type has a unique tow fitting so the towbar also acts as an adapter between the standard-sized tow pin on the tug and the type-specific fitting on the aircraft's landing gear. The tow bar must be long enough to place the tug far away enough to avoid hitting the aircraft and to provide sufficient leverage to facilitate turns. On heavy tow bars for large aircraft the towbar rides on its own wheels when not connected to an aircraft. The wheels are attached to a hydraulic jacking mechanism which can lift the towbar to the correct height to mate to both the airplane and the tug, and once this is accomplished the same mechanism is used in reverse to raise the tow bar wheels from the ground during the pushback process. 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]] which 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.
[[File:Airbus A340-313X, Lufthansa, Frankfurt am Main (Rhein-Main AB) (FRA FRF EDDF), 18.04.09 (5590387320).jpg|thumb|A towbarless tug at [[Frankfurt Airport]] transporting a [[Lufthansa]] [[Airbus A340-300]]]]
[[Image:Pins for pushback.jpg|thumb|Towbars are used to connect the tractor to the aircraft.]]
Towbarless (TBL) tractors do not use a towbar; they scoop up the nose landing gear and lift it off the ground. This avoids the time penalty of connecting/disconnecting a towbar, and entirely removes the cost/complexity of maintaining towbars on the ramp. The tug itself does not need to be particularly massive - the aircraft's nosewheel weight provides the necessary downward force. Lastly, a TBL tug is much shorter (compared to a tug+towbar system) and has only a single pivot point instead of one at either end of the towbar, so it has much simpler and precise control of the aircraft. This is very useful in general aviation settings with a wider variety of aircraft in more confined spaces than their airline counterparts.

Manufacturers of electric TBL tugs offer models capable of moving any aircraft from the smallest single-engine type 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 which must be adjustable to suit many aircraft types. Electric TBL tugs are gaining popularity among general aviation operators and [[Fixed-base operator|FBOs]] as an alternative to gas or diesel-powered conventional tugs. Being electric rather than internal combustion-powered, electric tugs are low-emission which is a major advantage for environmentally-conscious operators; this also enables the tug to be safely operated inside a closed hangar.

===Robotic tractor/tug===
The Lahav Division of [[Israel Aerospace Industries]] has developed a semi-robotic towbarless tractor it calls [[TaxiBot]] that can tow an aircraft from the terminal gate to the take-off point (taxi-out phase) and return it to the gate after landing (taxi-in phase). The TaxiBot eliminates the use of airplane engines during taxi-in and until immediately prior to take-off during taxi-out potentially saving airlines billions of dollars in fuel that is used. The TaxiBot is controlled by the pilot from the cockpit using the regular pilot controls.<ref name=Globes1>{{cite news|url=http://www.globes.co.il/serveen/globes/docview.asp?did=1000620538&fid=1725 |title=New IAI "taxibot" to save airlines billions |date=3 February 2011|access-date=9 July 2012 |work=[[Globes (newspaper)|Globes]]|publisher=Globes}}</ref>

[[British Airways]] has been using a similar sort of tug too. <ref>{{cite web | url=https://www.mototok.com/blog/remotely-controlled-aircraft-tugs-the-future-of-ground-handling | title=Remotely controlled aircraft tugs: The future of ground handling }}</ref>

==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 is unsafe, such as moving aircraft in and out of maintenance [[hangar]]s, or moving aircraft that are not under their own power.

Some airlines, notably [[Virgin Atlantic]], advocated towing aircraft to the holding point of the runway to save fuel and reduce environmental impact.<ref name="BBC">{{cite web|url=http://news.bbc.co.uk/1/hi/business/6203636.stm|title=BBC NEWS - Business - Virgin Atlantic move to save fuel|author=|date=3 December 2006|work=BBC.co.uk|access-date=17 March 2017}}</ref> However, the practice was discontinued after landing gear maintenance costs increased due to the stress put on the landing gear during the towing process.<ref name="Engineer">[http://www.theengineer.co.uk/in-depth/analysis/reducing-runway-emissions/1000252.article Ellie Zolfagharifard, "Reducing runway emissions", ''The Engineer'', December 7, 2009.]</ref>

Some fuel must still be burned to operate the [[auxiliary power unit]] to provide electrical and pneumatic power to run lighting, environmental and communications systems, unless the tug itself provides these sources of power, which some do. This method also places a larger workload on ground crews and equipment, especially if the aircraft and tow tractor ends up having to wait in a long line of aircraft.

==In media==
In an advertising campaign, also documented on the television show ''[[Fifth Gear]]'', a [[Volkswagen Touareg]] was used to pull a [[Boeing 747]]. 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 that reason.<ref name="YouTube Video: VW Touareg tows a 747">{{cite web|url=https://www.youtube.com/watch?v=WmM-635RR6o |archive-url=https://ghostarchive.org/varchive/youtube/20211221/WmM-635RR6o |archive-date=2021-12-21 |url-status=live|title=VW Touareg Towing a 747 Jumbo Jet - Fifth Gear|last=Fifth Gear|date=21 August 2014|publisher=|access-date=17 March 2017|via=YouTube}}{{cbignore}}</ref> This is the world record for the heaviest load towed by a production car.

==Gallery==
<gallery mode=packed>
File:Tow truck ekch.jpg|Pushback tug with the towbar behind
File:KLM Pushback tractor and ground power unit.jpg| Towbarless tractor
File:ILA 2008 PD 542.JPG|Towbarless tractor for smaller aircraft
File:T813 6x6 civil.jpg|A [[Tatra (company)|Tatra]] [[Airport tug T813 6x6|T813 6x6 Airport tug]]
File:Pushback tractor in front of Easyjet A319.JPG|A tug ready to push back an [[EasyJet]] [[Airbus A319]]
File:Unimog pushback.jpg|A [[Unimog]] being used as a pushback tractor
File:Aircraft towing, SE-LTU Saab 2000.jpg|A [[Saab 2000]] being towed by a small tow tractor at [[Ängelholm-Helsingborg Airport]]
File:De Havilland DHC-1 Chipmunk (G-AKDN) ground handled at Fairford 7Jul2016 arp.jpg|[[de Havilland Chipmunk]] manually ground handled at the 2016 [[Royal International Air Tattoo]], England
File:Batik air pk-lum pushback.jpg|An Indonesia Batik air A320 on pushback at Soekarno–Hatta International Airport
File:BelAZ 74271 aircraft tractor 2.jpg|[[BelAZ]] 74271 airport tug with double cab
File:Towbarless Aircraft tug NadHaf IAF Equipment.jpg|Towbarless tug (NadHaf) for [[fighter aircraft]] in [[Israeli Air Force]]
</gallery>

== See also ==
{{Commons category|Pushback tractors}}
* [[Aircraft ground handling]]
* [[Ground support equipment]]
* [[Visual Guidance Docking System|Visual Guidance Docking Systems (VGDS)]]

== References ==
{{Reflist}}

== Sources ==
* Operations Manual Bucher aircraft tractor Kp20FlApt13
* [[Schweizerisches Militärmuseum Full|Schweizerische Militärmuseum Full]]

[[Category:Aircraft ground handling]]
[[Category:Tractors]]
[[Category:Articles containing video clips]]

AviationSafetyX Wiki - User contributions [en]

Pushback (aviation)