Deriving Benefits from Alternative Aircraft-Taxi Systems (2016)

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1 This resource guide was produced as part of ACRP Project 02-50. Full documentation of the research conducted and findings compiled are presented in a final report that, while not being published, is available to future researchers and other interested parties by contacting ACRP. Airport managers, environmental agencies, and other parties in the aviation industry are becoming increasingly aware of the contribution of airport-related activities to local air quality, greenhouse gas emissions, and noise. Fuel is one of the key costs that airlines have to consider, and any fuel price volatility, such as that seen in 2008, can adversely affect profit margins. The majority of aircraft fuel is consumed during the cruise phase of flight, and there is very little that an airport or airline can do to reduce the costs of the fuel used during this phase. However, airlines can reduce fuel use, emissions, and costs during other phases of flights and while aircraft are on the ground through the following: • Reduced takeoff and climb thrust, as highlighted in the recently completed research con- ducted under ACRP Project 02-41, “Estimating Takeoff Thrust Settings for Airport Emissions Inventories” (Horton et al., 2014). • Increased efficiency during aircraft taxiing—for example, reducing the number of engines used during taxiing, although this approach may involve operating the remaining engines at a higher thrust setting. • Improved operational efficiency through programs such as NextGen (United States) and Single European Sky ATM [air traffic management] Research (SESAR, European Union). • Use of alternative fuels to reduce emissions of pollutants such as oxides of sulfur and particulate matter (PM) in compliance with future U.S. Environmental Protection Agency regulations. • Replacing the use of the aircraft main engines for taxiing with alternative aircraft-taxiing systems such as onboard alternative aircraft-taxiing systems or equipment similar to aircraft pushback tractors. This ACRP Project 02-50 resource guide is focused only on alternative aircraft-taxiing systems at U.S. airports; however, a large body of research from Europe has been incorporated where relevant. For context, Airbus (2013) estimates that a typical short-to-medium-range aircraft in Europe spends between 10% and 30% of its total flight time taxiing, constituting about 10% of its fuel consumption. It is assumed that similar proportions would also apply in the United States. A number of alternative aircraft-taxiing systems that are at different stages of development have the potential to enable an aircraft to taxi without the use of its main engines. When these alternative aircraft-taxiing systems are used, there is no associated aircraft main engine fuel burn, emissions, or noise, but these will be partly replaced by those of the alternative aircraft-taxiing system. However, main engines must be warmed up approximately 5 minutes before takeoff, resulting in aircraft main engine fuel burn, emissions, and noise. The net reduction in fuel burn, emissions, and noise will be a result of the length of time spent taxiing and the types of equipment C H A P T E R 1 Introduction

2 Deriving Benefits from Alternative Aircraft-Taxi Systems and engines used for the aircraft and the alternative aircraft-taxiing system. In some cases, the overall benefits will be limited. The potential also exists for increased costs [for purchase (or lease) of the alternate system, maintenance, and fuel]. However, there are other issues that should be considered before any fuel, emissions, and noise benefits can be realized. Key considerations for airport operators, aircraft operators, and ground service providers implementing these systems include the following: • Existing (and future) taxiing time. If the taxiing time is too short, then any benefit is likely to be minimal (i.e., up to approximately 5 minutes will be needed for main engine warm-up/ cool-down). • Existing (and future) aircraft fleet mix. Most alternative aircraft-taxiing systems are intended for the narrow-bodied market (e.g., Airbus A320 and Boeing 737), although there are external systems that can handle larger aircraft (i.e., as large as Airbus A380). • Nose-wheel landing-gear fatigue loading if standard aircraft pushback tractors are considered. • Aircraft main engines starting on the taxiways (or close to runway hold points) and the impact of a failed engine start (e.g., delays to other aircraft in the queue for takeoff). • Additional staff and training requirements. • Taxiing speed (including likely acceleration/traction needed for stop/start cycle at congested airports) and ability to cross active runways within a safe time period. • Necessary modifications to aircraft, including any necessary certification from the FAA. • Necessary modifications to airports, including infrastructure and land use. • Whether the system is pilot-controlled. • Likelihood of certification for noncertified alternative aircraft-taxiing systems. • Safety and visibility. • Communication with air traffic control (ATC) regarding engine starts. • Potential time savings. • Ownership of alternative aircraft-taxiing systems–airport, airline, or ground handler? Five types of alternative aircraft-taxiing systems are considered in this resource guide (see Figure 1): • Dispatch taxiing (e.g., using existing aircraft pushback tractor technology). • Semi-robotic dispatch taxiing (i.e., similar to a pushback tractor but using a hybrid external large tractor developed specifically for taxiing). Figure 1. Different types of alternative aircraft-taxiing systems (shaded).

Introduction 3 • Nose-wheel–mounted alternative aircraft-taxiing systems. • Main landing gear alternative aircraft-taxiing systems. • Replacement of the auxiliary power unit (APU) with an additional onboard taxi jet engine capable of providing sufficient thrust for taxiing. This resource guide has been developed for airport practitioners and other stakeholders. It provides information on potential cost, energy, and environmental benefits such as reductions in noise, emissions, and time, as well as potential challenges of implementing alternative aircraft- taxiing systems at U.S. airports. The resource guide includes the following: • Chapter 1: Introduction – Introduces the concept of alternative aircraft-taxiing systems – Introduces the outline structure of this resource guide • Chapter 2: Alternative Taxiing Assessment Matrix (ATAM) – Introduces and describes the ATAM tool, which is a spreadsheet-based tool that provides a useful compendium of benefits of and concerns associated with the different types of alternative aircraft-taxiing systems • Chapter 3: Discussion – Additional discussion of alternative aircraft-taxiing systems • Appendices – Appendix A: Detailed Description of Information in the ATAM: Provides detailed discus- sion of each of the benefits and concerns associated with alternative aircraft-taxiing systems included in the ATAM tool – Appendix B: Acronyms and Abbreviations – Appendix C: References