pushback: Definition from Answers.com

In aviation, pushback is an airport procedure during which an aircraft is pushed backwards away from an airport gate by external power. Pushbacks are carried out by special, low-profile vehicles called pushback tractors or tugs.

Although many aircraft can also move backwards on the ground using reverse thrust (a procedure referred to as a powerback), the resulting jet blast 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 aerodromes are usually subject to ground control clearance to facilitate ground movement on taxiways. 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 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. To have enough traction, the tractor needs to be heavy, and most models can have extra ballast added. A typical tractor for large aircraft weighs up to 54 metric tons and has a drawbar pull of 334 kN ^[1] 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. 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 but instead scoop up the nose wheel of an aircraft and lift it up off the ground, allowing the tug to manoeuvre the aircraft. This allows more secure control of the aircraft, allowing greater speeds, and lets aircraft be moved without anyone in the cockpit. ^[2] However, a towbarless tractor may be usable for fewer aircraft types than a conventional tractor.

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

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 hangars, 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.^[3]

Incidents

Incidents or accidents involving a pushback include:

• Garuda Indonesia Boeing 737-500, operating as Flight 238, collided with a Saudi Arabian Airlines Boeing 747-300. No casualties or injuries.

In the media

In an advertising campaign, also documented on the television show Fifth Gear, a Volkswagen Touareg was used to pull a Boeing 747. The car carried 4.3 tons of ballast in the form 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. ^[4]

Gallery

See also

• Aircraft ground handling
• FMC Technologies
• Ground Support Equipment
• Bliss-Fox Ground Support Equipment
• Visual Guidance Docking Systems (VGDS)

References