In today's #Avgeek article, we will write about the procedures and ways in which planes are moved from the parking lot to the rolls, which then go further towards the runway. pushback and powerback are the two basic ways to move an aircraft out of a parking position. Their main difference is that the pushback uses external force to push the aircraft, while the powerback uses the power of the aircraft engine to reverse.
Pushback is a procedure by which an aircraft is pushed out of a parking position by an external force, that is, using vehicles specially designed for that purpose. The low center of gravity vehicles used for pushback are called pushback tractors or tugs. According to aviation tradition, the name tractor is used because in the early days of aviation, pilots sometimes resorted to the help of local farmers and their tractors to move an aircraft without the use of an engine. However, although tractors can still be seen at airports, including Croatian airports, their purpose is primarily to tow luggage carts and other airport equipment.
Today, two types of pushback vehicles are most commonly used depending on whether they use an additional bar to connect and push the aircraft or not. The first group of pushback vehicles uses specially manufactured bars on two wheels with which the pushback vehicle is connected to the aircraft and are called Towbar tractors or tugs. The second group of pushback vehicles connects directly to the aircraft itself and do not use a special connecting bar, and are called Towbarless tractors or tugs.
As a rule, airports have both types of pushback vehicles among their vehicles. Also, some airlines have their own procedures that apply to cases when they use towbar vehicles at a particular airport, and when they are allowed to use towbarless vehicles. Recently, there has been a growing trend of purchasing and using towbarless vehicles, as in their case it is not necessary to have different bars for different types of aircraft and they require less manpower to participate in pushback. Also, the design of these vehicles allows for better visibility of the space in which they drive and reduces the possibility of injury to people when handling the bar. On the other hand, the biggest advantage of pushback vehicles with a bar is the lower maintenance price of these conventional vehicles, and this advantage is especially pronounced at airports where a small number of different types of aircraft operate.
Example of a pushaback with a towbar:
Example of pushback with towbarless vehicle:
Unlike pushback in the case of powerback, the aircraft moves backwards from the stand using its own engine power and reversible thrust, or thrust reversal. For purely explanatory reasons, a reversible thrust is a redirection of the thrust of an aircraft that allows the aircraft to slow down during landing as it acts in the opposite direction to the direction of the aircraft’s forward motion. Thrust diversion systems are located on many jet aircraft so that they can slow down the aircraft immediately after touching the ground, thus reducing brake wear and allowing a shorter stopping distance of the aircraft. This system is also often used by aircraft with engines that have built-in propellers.
Aircraft whose engines are installed high above the ground are generally suitable for powerback use. Some of the aircraft that are suitable and that use powerback more often are the MD80, DC9, B727 and B737. Unlike pushback, which requires more equipment and manpower, the biggest advantage of powerback is the speed of moving away from the stand to the rolls. It is interesting to note that most commercial passenger aircraft must turn off the air conditioning system during the powerback so that the exhaust gases do not penetrate into the passenger cabin.
Pushback vs. Powerback
Perhaps reading the text has led you to the question of why powerback is so rarely used when it requires less equipment and manpower, and in addition the transition of aircraft from parking slot to rolls is much faster. As we have stated many times in previous texts, the basic guiding thought in aviation procedures is to reduce the possibility of injury to people and damage to the aircraft itself. So safety comes first.
From a safety point of view, powerback poses a significantly higher degree of threat than pushback itself. While the aircraft is parked, a large number of vehicles and people move around it, and it is very likely that some small object will remain on the ground, such as a screw, torn luggage tag, broken equipment, etc. Despite the fact that before the arrival and departure of the aircraft FOD check (Foreign Object Debris), ie the removal of all foreign objects from the surface on which the aircraft is moving, starting the aircraft engine and their suction power could lead to unwanted situations on the stand. Also, it should be emphasized that due to the operation of the engine on the stand itself, there can be undesirable consequences for ground personnel, vehicles, other equipment and even the bridges connected to the passenger terminal. Based on all of the above, using pushback reduces the risk of possible damage.
All in all, in Europe, as a rule, only aircraft with propellers use powerback, while in the USA, some larger commercial passenger planes use powerback. Powerback is therefore often used in military aircraft and seaplanes.
If you happen to have the opportunity to see the powerback live on a larger commercial passenger aircraft, definitely don't forget to record it and send us a recording! We will be happy to look at it and publish it :)!