Fri 24 Feb 2017 – It is estimated around 18 million tonnes of CO2 are emitted annually during aircraft taxiing operations and efforts other than reduced engine taxiing have been ongoing for over a decade to find alternative, innovative solutions to save fuel, time and emissions. However, those efforts have had mixed results. A Honeywell/Safran EGTS joint venture was abandoned last year. A similar joint venture involving L-3 and Crane Aerospace, called GreenTaxi, also disappeared off the radar. This has left just two mainstream solutions: the WheelTug nose wheel electric drive system that propels a narrowbody aircraft from the stand to the runway, and IAI’s TaxiBot semi-robotic pilot-controlled vehicle. However, this has not dented the enthusiasm of IATA in seeing the potential fuel and emissions saving benefits of autonomous taxiing and has announced it will hold its second E-Taxiing conference in Singapore in May.
A report by UK cross-industry group Sustainable Aviation found that 30% of total CO2 emissions at Heathrow Airport came from aircraft taxiing and the use of auxiliary power units (APUs). Savings of 100,000 tonnes of CO2 per year have been calculated at Heathrow from reduced engine taxiing and APU substitution. On a global level, IATA has estimated a CO2 savings potential in the order of 6 million tonnes annually.
A 2010 MIT study found domestic US flights emit about 6 million tonnes of CO2, 45,000 tonnes of CO, 8,000 tonnes of NOx and 4,000 tonnes of HC taxiing out for take-off. These pollutants contribute to low-altitude emissions, directly impact local non-attainment of air pollution standards and represent a concern for human health and welfare, said the study.
Another study by Delft University of Technology in the Netherlands estimated fuel used during taxiing operations in 2012 cost around $7 billion and emitted in the region of 18 million tonnes of CO2.
Driven by increasing fuel costs, environmental concerns and a requirement by airlines to cut turnaround times at airports, a number of initiatives were launched that went further than reduced-engine operations when an aircraft taxis in or out. Working with Lufthansa Technik, L-3 Communications and Crane Aerospace started development of an electric taxiing system that was to be mounted on the main landing gear of Airbus and Boeing narrowbody aircraft, and a ground trial took place at Frankfurt Airport in 2011 on an A320. However, by 2013 the project had been quietly dropped.
That same year, at the Paris Air Show, Honeywell and Safran demonstrated their main landing gear-mounted Electric Green Taxiing System (EGTS) on an Airbus A320. At the Farnborough Air Show in July 2016, Honeywell announced it was halting the project “due to dramatically lower oil prices and the current aviation industry’s economic environment,” despite claiming widespread customer interest.
This has left the field to privately-owned, Gibraltar-based WheelTug to pursue its concept of placing two electric motors powered by the onboard APU in the nose wheel of a narrowbody aircraft to allow backward as well as forward movement. The company started operation back in 2005, ground testing the concept on an Air Canada Boeing 767 in Arizona. Since then, development has been slow and a number of timelines missed, including an expectation of a FAA Supplemental Type Certificate (STC) – a necessity before the system can be used in commercial flight operations – on the Boeing 737NG by the end of 2009. In 2014, the company said it was hoping for FAA certification by early 2016.
Neither Boeing nor Airbus is supporting the development but WheelTug says it has received letters of intent from 22 airlines for the installation of the system on almost 1,000 aircraft. Instead of purchasing the system, airlines would lease it from WheelTug and share cost savings, which the company estimates could amount up to $1 million annually per aircraft. It says the system uses one-sixth of the fuel currently burned on average while taxiing.
The Israel Aerospace Industries’ (IAI) TaxiBot solution is further down the certification route since it does not require modification to an aircraft. In September 2016 an STC was issued by the European Aviation Safety Agency (EASA) and the Civil Aviation Authority of Israel (CAAI) for the Boeing 737NG, so completing certification for the whole 737 family. IAI reports the TaxiBot has successfully completed certification testing of the Airbus A320 family and it expects to receive formal certification by the middle of March.
The TaxiBot vehicle lifts and holds the aircraft nose wheel, and then transports the aircraft from the terminal gate to the runway and back, without using the aircraft’s own engines. It has been dispatch-towing Lufthansa 737 Classic commercial flights departing out of Frankfurt Airport since November 2014. Since 2008, IAI and its risk-sharing manufacturing partner TLD have been cooperating with Lufthansa LEOS in TaxiBot’s development, with the support of Airbus and Boeing, says IAI.
The company claims considerable interest has been shown from leading airlines, ground handling companies, airports and leasing companies around the world, with several working groups actively studying and preparing to introduce TaxiBot at leading airport hubs in North America, Europe and Asia. However, no customers have yet been announced.
A California-based company, Aircraft Propulsion Technologies (APT), has been working on an alternative on-board propulsion system for a number of years, for which it is still seeking support. APT has a patent (enter 8109464 here) issued in 2012 for its concept of replacing the APU in narrowbody aircraft with a small, certified turbojet engine that is sized for taxiing operations in addition to normal APU functions.
“The system would reduce fuel burn, emissions, jet blast and noise during taxiing because the small modern and efficient Full Authority Digital Electronic Control (FADEC) certified engine would consume less fuel and be quieter than conventional taxiing on main engine power,” explained APT’s Brij Bhargava. “It is the only onboard system that enhances aircraft safety on the ground and in flight, and the system does not require any changes to well-established airport ground operations.”
He noted that as far back as 2005, Boeing had plans to design, develop and certify a nose wheel taxi system, and had a patent (enter 7445178 here) assigned in 2008. But, he said, Boeing abandoned the programme and has never endorsed any other powered landing gear system.
“Over the past decade or more, several attempts have been made to reduce emissions from airplane taxiing operations by replacing main engine power with an electric alternative but none of these efforts has yet proven to be a practical solution,” he said.
However, WheelTug continues to press on with its nose wheel system development and last month it announced Canadian leisure carrier Air Transat would be supplying a Boeing 737 for testing in Montreal in exchange for a free system. This follows an announcement earlier in January that the FAA had approved the company’s certification plan for the system.
“We’ve done the majority of things we can do to improve fuel efficiency so we’re at the point now of looking for more out-of-the-box kind of ideas,” said Keith Lawless, Air Transat’s Senior Director of Business Sustainability and Improvement.
WheelTug and IAI TaxiBot are respectively Diamond and Gold sponsors of IATA’s E-Taxi Conference that will take place in Singapore on May 23-24. The event follows the Aircraft Taxiing Systems Conference held by IATA in Miami in February 2015.
“The well-received Miami conference looked at research and evaluation, and the 100+ participants demanded a follow-up conference to discuss subsequent developments,” said Klemen Ferjan, Airline Performance Metrics Manager at IATA. “Therefore, this next event will focus mainly on the technological readiness and regulatory approval of alternate taxiing solutions. Note that we have changed the name to capture several benefits of these solutions – ‘E’ in E-Taxi stands not only for Electric but also for Efficient and Environmental.”
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