Final answer:
The procedure of moving an aircraft backward using a tug is called pushback, important for safety and efficiency on the tarmac. It ensures the aircraft reaches a safe engine-start position, as reverse thrust isn't usually suitable at airports.
Step-by-step explanation:
The procedure in which a tug moves an aircraft backward from an operational stand to its engine-start position is commonly referred to as pushback. Pushback is used in situations where an aircraft cannot reverse under its own power. The significance of pushback lies in its necessity for safety and efficiency on the ground. Specifically, the final velocity of an aircraft after pushback is less than the initial velocity because the goal is to move the aircraft safely to a position where it can start its engines without endangering ground personnel or infrastructure. Jet engines can use reverse thrust to slow down or even move backward, but this is often not feasible or safe in congested airport environments. As an example, during an emergency such as the one faced by Captain Pearson and First Officer Quintal aboard a Boeing 767, the lack of engine power meant that their aircraft essentially became a large glider. In that particular situation, reverse thrust was not an option. This story emphasizes the importance of understanding aircraft movement both in the air and on the ground.