Ground support equipment (GSE) is the machinery that serves aircraft on the ground at an airport. The two best-known kinds are tugs, which push an aircraft back from the gate, and loaders, which lift baggage and cargo into the hold. An airliner's wheels have no motor, so it cannot drive backwards. Its engines could push it backwards, but the blast of air from the engines would endanger people and equipment near the gate. So a tug moves the aircraft back before the pilot starts taxiing.
At a busy airport, dozens of vehicles work around each aircraft in the short time between landing and take-off, which is often under an hour. Tugs, baggage loaders, catering trucks and fuel trucks must reach the aircraft at the right time. If one is late, the flight leaves late. Each vehicle is a machine of the same sort as those in heavy equipment. The buyers are airlines and the ground-handling companies that serve aircraft for them, and an airport operator may buy some vehicles too. Tugs are heavy because they must move an aircraft that weighs tens or hundreds of tonnes.
Say a tug at Kochi airport pushes a narrow-body aircraft back from its gate with 180 passengers on board. A telematics device on the tug records how long the push took, how much fuel it used and whether the engine reported a fault. The ground-handling company uses these records to plan service. A tug that fails during a push-back can block a gate, so the company wants to repair it before that happens. It orders replacements through service parts management.
GSE also connects to the airline's systems. The departure control system (DCS) decides which baggage and cargo go on the flight, and loaders put exactly that into the hold. Like other heavy machines, GSE is sold with service for many years, as in service after the sale. Many newer vehicles run on batteries instead of diesel, because they work at airports where fumes and noise matter.
For the aircraft itself, see aircraft maintenance (MRO), which covers the checks and repairs done on it.