# Prediction and Analysis of Airport Surface Taxi Time: Classification, Features, and Methodology
## 2 Classification of Research Perspectives
### Type of Movement  
From the perspective of the movement category, surface taxi time prediction research is categorized into two main areas: arrival aircraft taxi time prediction and departure aircraft taxi time prediction. The arrival aircraft follows predetermined taxi routes set by the air traffic service unit (ATSU), resulting in relatively stable taxi times. Conversely, the departure process for aircraft is more complex and variable, making accurate prediction of departure taxi time vital in optimizing runway utilization and achieving flexible aircraft pushback control. There is a close correlation between aircraft pushback control, runway utilization optimization, and taxi time prediction. The goal of aircraft pushback control is  
Figure 5: Definition of actual taxi time.  
to minimize taxi time, reduce fuel consumption, and improve takeoff efficiency. The goal of runway utilization optimization is to maximize runway usage efficiency, reduce wait time, ensure aircraft can take off and land smoothly as planned, and reduce congestion and delays. The goal of taxi time prediction is to accurately estimate how long an aircraft will be on the surface in order to better sequence the pushback and arrival of flights. Optimizing aircraft pushback control may involve adjustments to taxi speeds and routes, which can affect taxi time and runway utilization. Conversely, optimization of runway utilization may also reduce wait time and optimize taxi routes by adjusting the aircraft pushback sequence.  
The specific arrival and departure process is shown in Figure 6. The arrival process encompasses the sequence of events in which an aircraft receives landing instructions from the tower controller, touches down on the designated runway, exits the runway via the fast departure route, and then taxis to the assigned parking stand under the guidance of the ground controller. At the parking stand, the aircraft undergoes maintenance and receives various ground services. On the other hand, the departure process involves receiving clearance instructions from the ground controller. The aircraft is then pushed back from its parking stand using a trolley or tractor and taxis to the runway gate along the designated taxiway, following the controller's instructions. Once the aircraft joins the queue of departing flights, it awaits its turn for takeoff. Finally, the aircraft follows the tower controller's instructions to approach the runway and complete the takeoff task [30].  
Furthermore, considering operational aspects, arrival aircraft have the advantage of directly taxiing into the stand without requiring a tractor, resulting in shorter taxiing durations. On the other hand, departure aircraft cannot directly face the apron during taxiing out and need tractors for pushback, leading to longer taxiing durations [31].  
Due to the high dynamics and uncertainty of the surface departure process, current research efforts, both domestically and internationally, primarily focus on surface taxi time prediction for departure aircraft. This aspect can be further divided into two categories: surface taxi time prediction, which concentrates solely on the departure process; and surface taxi time prediction, which takes into account the influence of arrival aircraft.