Progress on green aircraft taxiing solutions is slow – unlikely to make huge improvements in fuel use or NO2?

For several years there have been attempts to cut the amount of aircraft engine noise and CO2 emissions from taxiing. Worldwide perhaps 2.6% or so of total aviation carbon emissions might be from taxiing, and it increases noise close to the airport. Some of the electrical solutions to the problem have come to nothing, and been quietly dropped. eg. a Honeywell/Safran EGTS joint venture that was abandoned last year, and a joint venture involving L-3 and Crane Aerospace, called GreenTaxi, also disappeared. There are two remaining possible systems:  WheelTug nose wheel electric drive system and IAI’s TaxiBot semi-robotic pilot-controlled vehicle. IATA is enthusiastic about how these will cut fuel consumption from taxiing in future, and there is a conference on the subject in Singapore in May. The aviation lobby group “Sustainable Aviation” has said Heathrow could eventually, if there was the technology, cut “100,000 tonnes of CO2 per year”. That is about 0.5% of its total emissions of some 19MtCO2. WheelTug requires a plant to be modified, and the APU to power two motors on the front wheel.  Neither Boeing nor Airbus is supporting the development.  The TaxiBot system is further down the certification route since it does not require modification to an aircraft. It lifts and holds the aircraft nose wheel, and then transports the aircraft without using the aircraft’s own engines.


Early promise of green aircraft taxiing solutions has yet to materialise although progress on regulatory approvals

Fri 24 Feb 2017

(GreenAir online)

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.  [It seems to work with the Boeing 737 but not with the A320. More details at  There is no mention of it being used for wide-bodied planes. AW comment]  

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).  [This may be 30% of emissions just in the airport and up to 3,000 feet. It is not 30% of the CO2 from flights using Heathrow, which is a massive higher figure. AW comment.]

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.  [CO2 emissions by Heathrow are around 18 million Tonnes of CO2 per year, so this is about 0.5% of that. Welcome, but not large, in the grand scheme of things. AW comment] 

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.  [Globally the aviation sector emits around 675 million tonnes per year, so 18 tonnes is 2.7% of that. AW comment]

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.  [It adds weight to the plane, but saves time on the ground, compared to TaxiBot.  AW comment] 

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.  [Implies it needs modification of the aircraft, before it could be used. AW comment] 

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.  [It seems there is a version for narrow-body planes, that is relatively far advanced. The version for wide-bodied planes seems much further behind.  [ Details at  and  ]

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.”


Related GreenAir Online articles:


Heathrow said in Quarter 4 2015:

“During 2015 we undertook a detailed study into the use of “Taxibot” – a semi-robotic, pilot-controlled towing tractor that tows the aircraft close to the take off point without running engines so significantly reducing emissions on the airfield. While space constraints at Heathrow currently mean Taxibot isn’t able to be immediately implemented, we are considering its use in the future. We are also working with airlines investigating the use of electric taxiing systems built into the aircraft nose wheel.”


Heathrow Air Quality Strategy 2011–2020

This states:

“Aircraft NOX emissions are broken down further into a number of ‘activities’ in Fig. 2. Take-off roll is the biggest emissions source (46%); though taxiing and use of auxiliary power units (APUs) are almost as large when considered together. These areas all impact on local air quality and we have developed actions to reduce their local impacts.”

Figures below are for NOx. 



IAI’s TaxiBot in Final Stages of Certification for the Airbus 320

The TaxiBot narrowbody tow-tractor design, seen here handling a Boeing 737, is about to receive type certification for the Airbus A320. (LH LEOS)

The TaxiBot narrowbody tow-tractor design, seen here handling a Boeing 737, is about to receive type certification for the Airbus A320. (LH LEOS)

Israel Aerospace Industries (IAI) has announced certification tests on its TaxiBot tow-tractor’s ability to manoeuvre Airbus 320neo airliners were completed successfully on December 8th, 2016.
The TaxiBot is a semi-robotic pilot-controlled vehicle for dispatch towing airliners from terminal gates to the runway and back, without using the aircraft’s own engines. TaxiBot started dispatch-towing commercial Lufthansa Boeing 737 (Classic) flights departing out of Frankfurt Airport in November 2014.
The A320 certification tests took place at Airbus’ facilities in Toulouse, France, where the tractor reached its maximum speed of 23 knots, performed multiple turns at different speeds and tight turns at low speed. An engine start of one and both engines of the A320neo during TaxiBotting was performed satisfactorily, as were other tests conducted by Airbus test pilots.
According to Robert Lafontan, Airbus Senior Vice President Engineering, the formal EASA approval for TaxiBot /A320 operations is expected at the beginning of 2017.
Since 2008, IAI, together with its industrial risk-sharing partner TLD, has been cooperating with Lufthansa LEOS in the development of the TaxiBot, with support of both OEMs Airbus and Boeing. Lufthansa LEOS has integrated the TaxiBot project into its E-PORT-AN initiative, aimed at taking passenger aircraft towing and surface-traffic performance beyond the existing limits of environmental sustainability at Frankfurt Airport.
Ran Braier, Director of Civil Robotics at IAI commented: “The successful certification of the A320 is an important milestone for the TaxiBot programme. Adding the certification of the A320 family to the already certified B737 family covers 70% of all the worldwide commercial airlines flights, which could be provided with TaxiBot service. Certification will enable operation of this innovative system with major airline fleets in leading airports, revolutionising the commercial aviation industry, while saving millions of dollars in fuel costs, improving operations and contributing to the global environment.”