Pushback
From Wikipedia, the free encyclopedia
A pushback is a technique where an aircraft is pushed backwards away from an airport gate, where there is usually no room for a large aircraft to turn around. Pushbacks are carried out by special, low-profile vehicles called pushback tractors or tugs.
Although aircraft can also reverse using reverse thrust (called doing a powerback), this may cause damage to the terminal building or equipment because of jet blast. Engines close to the ground may blow sand and debris forward and then suck it in to the engine, causing damage. It is also very noisy. A pushback using a tractor is therefore the preferred way.
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[edit] Procedure
Pushbacks at busy aerodromes are usually subject to controller clearance to facilitate ground movement on taxiways. Once clearance is obtained, the pilot will communicate with the pushback truck driver (or a ground handler walking along 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 truck 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 so it is disconnected from the pilot's controls and can be turned by the pusback truck. Once the pushback is completed, the towbar is disconnected, and the bypass pin (if used) is removed. The ground handler will show the bypass pin to the pilots to let them know it has been removed. The pushback is then complete, and the aircraft can start taxiing forward under its own power.
[edit] Equipment
There are two types pushback vehicles, Tow-Barless (TBL) and conventional. Conventional tugs use tow bars to connect to the nose wheel of the aircraft. Then the tractors push the aircraft to a safe position before disconnecting it. 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. Often, the driver's cabin can be raised for increased visibility, and lowered to fit under aircraft. The Tow-Barless tug scoops up the nose wheel of an aircraft and lifts it up off the ground, allowing it to manoeuvre the aircraft. This saves time
The tow bar 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.
[edit] Other ground movements using the same equipment
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.
Very small aircraft may be moved around by 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.
