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Airport Activity Module

The purpose of the Airport Activity Module is twofold: firstly, to model ground and low altitude operations and congestion to determine LTO emissions; and secondly (and uniquely among similar policy assessment models), to develop a flight routing and scheduling model that captures airline response to limited airport capacities and resulting delay (e.g. via re-routing, changing aircraft type, etc.).

The Flight Routing & Scheduling Model generates aircraft trips according to segmented passenger and freight flows. Based upon the passenger and freight flows coming from the Air Transport Demand Module, this model outputs aircraft trips, in the form of a flight schedule, to the Aircraft Movement Module and to an internal LTO Operations Model. Aircraft classes used are also output to the Aircraft Technology & Cost Module, which returns costs and emissions (the latter to the internal LTO Operations Model). The generation of the schedule includes identification of aircraft sizes, flight frequencies, departure times, and passenger load factors, by flight segment. These factors are modelled as a function of passenger and freight demand, segment length, and in future developments of the model, average delay (from an internal Delay Calculator) and aircraft cost (from the Aircraft Technology & Cost Module) to capture airline response behaviour. These relations are derived from current and historic schedules, demand data, load factors, delays, and aircraft class and size statistics.

Alternatively to the Scaled Routing Model in the Air Transport Demand Module, the Flight Routing & Scheduling Model also simulates the airline response to capacity constraints. By maximizing airline profits, i.e., the aggregate difference between airline revenues and costs for each possible flight segment, a linear optimization routine allocates passengers to various routes in different periods of the day, subject to the available aircraft fleet. This model will reproduce the global routing structure in the base year and endogenously adjusts the routing structure to capacity constraints, eventually resulting in a changing air traffic network over time. The formulation of this model has just begun and first tests based upon a limited set of airports are promising. 

The internal LTO Operations Model includes two functions: modelling aircraft ground operations; and modelling landing and take-off operations. The outputs of these models are LTO path, taxi and flight times, and emissions (calculated relative to emissions by class input from the Aircraft Technology & Cost Module), which are direct inputs to the Local Air Quality Module. The modelling of ground operations includes simulating taxi demand and unimpeded taxi times. Taxi demand is defined by the flight schedule input from the Flight Routing & Scheduling Model, and airborne delay input from the Aircraft Movement Module. Unimpeded taxi times are obtained directly from data for airports in some regions (e.g. US, EU), whilst parametric modelling based on other airport characteristics is required for those regions for which it is not available.

Landing and take-off operations are modelled according to flight path and thrust requirements, as defined by ATC and pilot procedures. This data is also available for some regions, whilst parametric modelling is required for others.

The internal Delay Calculator includes three functions: modelling aircraft ground delays; estimating airborne arrival holding requirements; and compiling total delay to passengers and freight. Detailed modelling of aircraft ground delay and airborne arrival holding requirements would include modelling multiple separate queues for gate delays, taxiing, runway departure queuing, airborne arrival holding, and arrivals waiting for gates. In the simplest AIM implementation, these delays are modelled using single arrival and departure queues, constrained by the airport capacities (received as inputs from an internal Airport Capacity Model) and ground stop requirements propagated upstream from the air (received as inputs from the Aircraft Movement Module). These models are derived according to average departure and arrival delays. Total delay to passengers and freight is calculated relative to scheduled and unimpeded arrival times, and includes ground delay and airborne delay input from the Aircraft Movement Module. Total delay is output to the Air Transport Demand Module and internal Flight Routing & Scheduling Model.

The internal Airport Capacity Model models airport and airport component (e.g. runway, taxiway and gate) capacities for input to the internal Delay Calculator. Such airport capacities, filtered by runway configuration and meteorological condition, are directly available for some airports, whilst more sophisticated modelling according to available airport characteristics is required for others.
Finally, the Airport Activity Module is designed to take as input various policy options aimed at influencing the environmental impact of air transport. These include:

  • Changes in airport infrastructure, such as new airports, runways, terminals, gates, and taxiways; and changes in airport equipage
  • Changes in procedures, such as separation requirements; and specific operational procedures, such as a “starting grid” concept, or land and hold short operations (LAHSOs)
  • Changes in aircraft operated, including changing size, capabilities (e.g. autoland), or passenger load factors
  • Changes in scheduling, including airlines “de-peaking” schedules as demand approaches capacity, and changes in slot management