Electric Taxiing: The Hurdles for Greener Aviation

The dream of quieter, cleaner airports with aircraft gracefully sidestepping the need for their thirsty jet engines during taxiing has long been a tantalising prospect in aviation. Electric taxiing systems, which utilise electric motors integrated into the aircraft's landing gear, promise to slash fuel consumption, reduce harmful emissions, and minimise noise pollution on the ground. However, despite initial enthusiasm and several high-profile demonstrations, the widespread adoption of this technology has been met with considerable economic and technical challenges, leaving many projects grounded or deferred.

The Allure of Electric Taxiing

The fundamental concept behind electric taxiing is elegantly simple: by disengaging the main engines and employing electric motors powered by the aircraft's auxiliary power unit (APU) or a dedicated battery system, aircraft can manoeuvre on the tarmac efficiently. This not only conserves precious fuel, especially during lengthy taxiing periods, but also significantly cuts down on the release of greenhouse gases and particulate matter. Furthermore, the reduction in engine noise during ground operations would contribute to a more pleasant environment for airport communities.

The potential benefits were first showcased in 2005 by Boeing Phantom Works and Chorus Motors, who fitted an electric motor to the nosewheel of a Boeing 767. This demonstration paved the way for companies like WheelTug to emerge, aiming to commercialise this innovative approach to ground movement.

A History of Demonstrations and Setbacks

The journey towards electric taxiing has been marked by a series of ambitious projects and subsequent disappointments. In 2011, the German Aerospace Center (DLR), in collaboration with Airbus and Lufthansa Technik, successfully tested an electric-driven nosewheel on an Airbus A320, powered by a zero-emission fuel cell. Simultaneously, a separate initiative by Lufthansa, L-3 Communications, and Crane Aerospace explored electric taxiing using motors in the main wheels of an A320. Despite these advancements, the GreenTaxi project, as it was known, was eventually discontinued.

Another notable effort was the joint venture between Honeywell and Safran, which presented their Electric Green Taxiing System (EGTS) at the Paris Air Show in 2013. This system, demonstrated powering an A320 solely through main wheel drive and APU power, garnered significant attention and support, with Air France and Airbus initially backing its development. However, the economic climate, particularly the dip in oil prices in 2016, led Honeywell to terminate the joint venture. While Safran continued development independently, their plans to equip A320s were ultimately shelved in 2019 due to Airbus citing insufficient system performance and maturity.

The Core Problem: Benefit Versus Cost

The primary obstacle hindering the widespread adoption of electric taxiing systems boils down to the challenging ratio of benefit to cost in commercial airline operations. While the technology itself has been proven to work through numerous tests, the economic viability for airlines remains a critical question.

For systems designed as aftermarket modifications for older aircraft, the potential benefits are theoretically higher, as these older fleets may be less fuel-efficient overall. Conversely, integrating electric taxiing into the design of *new* aircraft from the outset could potentially lower the integration costs. However, a significant hurdle for Original Equipment Manufacturers (OEMs) is that the benefits are more pronounced for older, shorter-range aircraft.

The Weight Penalty

A key factor influencing the cost-benefit analysis is the added weight of the electric taxiing system. For longer flights, the extra weight carried by the aircraft translates into increased fuel consumption, which can offset the fuel savings achieved during electric taxiing. As the market has seen a shift towards longer-range, more fuel-efficient aircraft, such as the Airbus A321LR, the perceived advantage of electric taxiing diminishes for these newer models.

Market Dynamics and OEM Incentives

The lack of a strong natural incentive for OEMs to integrate these systems into new aircraft designs is a significant impediment. Manufacturers are focused on optimising aircraft for overall flight efficiency, and the added weight and complexity of an electric taxiing system, especially when its benefits are less pronounced on long-haul flights, presents a difficult trade-off. This means that the most promising avenue for fielding the technology in the near term lies with aftermarket modifications.

WheelTug: The Remaining Hope

Currently, WheelTug stands as the primary company actively pursuing the development and certification of an electric taxiing system for existing airliners. The company has faced a protracted development cycle, with initial plans for Delta Air Lines to implement the system on its Boeing 737NGs dating back to 2009.

WheelTug has been working towards supplemental type certification for the 737NG, with a target for entry into service in early 2022, followed by plans for the A320. A public demonstration at Memphis International Airport in September 2021 showcased a pre-production system fitted to a 737-800, highlighting the system's capabilities.

Despite these efforts, the path to widespread adoption remains challenging. While WheelTug reports letters of intent from over 25 carriers for more than 2,000 aircraft, indicating growing airline interest, the economic realities continue to shape the market's response. The company's CEO, Isaiah Cox, acknowledges that airlines are increasingly supportive, but the inherent design considerations for OEMs remain a barrier.

The Future Outlook

The future of electric taxiing in commercial aviation hinges on several factors. For aftermarket solutions like WheelTug, continued progress towards certification and demonstrating clear, measurable economic savings will be paramount. The success of these systems on older, shorter-range aircraft could build momentum and encourage further development.

Looking ahead, the integration of electric taxiing systems into the design of the *next generation* of single-aisle aircraft presents a more promising long-term prospect. As the aviation industry faces increasing pressure to minimise its carbon footprint, a concerted effort to incorporate such technologies from the initial design phase could lead to more efficient and environmentally friendly aircraft. This would allow for optimised weight distribution and power management, potentially unlocking the full benefits of electric taxiing.

For now, the industry watches closely as WheelTug navigates the complex landscape of aviation certification and airline economics, hoping to bring the promise of greener taxiing to the skies.

Frequently Asked Questions

Q1: What is the main advantage of electric taxiing?
A1: The primary advantage is the reduction in fuel consumption, emissions, and noise during aircraft ground operations.

Q2: Why hasn't electric taxiing been widely adopted yet?
A2: The main reason is the unfavorable cost-benefit ratio for airlines, particularly due to the added weight of the system on longer flights and the lack of strong incentives for aircraft manufacturers to integrate it into new designs.

Q3: Which aircraft are most likely to benefit from electric taxiing?
A3: Older, shorter-range aircraft tend to benefit more, as the fuel savings during taxiing are more significant compared to the overall fuel burn of longer flights.

Q4: Are there any companies currently developing electric taxiing systems?
A4: Yes, WheelTug is the most prominent company actively working on developing and certifying an electric taxiing system for existing airliners.

Q5: What is the role of the Auxiliary Power Unit (APU) in electric taxiing?
A5: The APU is often used as the power source for the electric wheel motors during taxiing, as it is already present on the aircraft and can operate independently of the main engines.