ABSTRACT
Civil aviation has steadily increased over the past decades and plays an essential role in connecting
people and countries across the world. According to the International Civil Aviation Organization
(ICAO, 2018), passenger traffic has grown with an average of 5.4% between 1995 and 2015. ICAO
estimates the demand for aviation to continue increasing by an annual rate of 4.3% until 2035 and
4.1% until 2045. Among several crucial objectives of air transportation system problems, the
minimization of fuel consumption has a profound impact on both the economic viability of airline
companies and the impact of air-transportation in the environment.
Although aviation is not currently the leading cause of global warming, industry development, and
the increase in air transportation will make it a significant factor for global warming over the
coming decades. Predicting the impact of aviation on economic and environmental systems
requires investigations at different stages of air transport operations. One of the strategies to reduce
the fuel consumption of aviation is to optimize the fuel burn during airplane ground movement
(taxiing) in airports. The main reason is that aircraft ground movement is a significant source of
fuel consumption and emissions at an airport (e.g., it is estimated that aircraft burn about 7% of
their fuel during this stage of the flight). Among different ways of taxiing operation in an airport,
electrification of ground transportation has proven to be one of the most efficient ways which have
many advantages such as reducing fuel consumption and emission of greenhouse gases with low
maintenance cost. However, it should be noted that electric-powered vehicles can be a beneficial
and efficient way of taxiing in airports if the electricity is clean. Clean electricity is produced from 
IV
renewable and non-emitting sources such as wind, sun, and water. Using electric-powered vehicles
in airports might not be the optimal option if the electricity is produced by burning fossil fuels like
coal. Nowadays, in many provinces of Canada, the produced electricity is clean, and the
government is determined to have 90% clean electricity across Canada by 2030.
The presented study discusses the scheduling of aircraft towing tractors at the airport in order to
minimize the fuel consumption and environmental emission of airplane engines and towing
tractors. In this study, we developed a Mixed Integer-Linear Programming (MILP) model to
schedule electric-powered towing vehicles (pushback Tugs) to provide taxiing services to aircraft.
The proposed MILP solution enables aircraft to request a towing vehicle when it is available or
perform traditional taxiing operations by using aircraft engines to minimize operating costs, which
includes delay/earliness costs, fuel consumption cost, and towing cost. We concluded that the
hybrid system for taxiing operation which includes both traditional engine powered solutions and
the proposed electric-powered towing vehicle approaches, is the optimal solution. Through
sensitivity analysis, the proposed taxiing operations planning model determines the optimum
number of towing vehicles in an airport.