Hail and Ride

Simon Warburton examines the three-way battle between the new aircraft ground propulsion systems each promising to radically improve flow management.
Airlines are eagerly looking to capitalise on what are claimed to be substantial savings on offer by electronic or e-taxiing systems.
That prize is one air traffic managers are well aware of, but is viewed with a certain amount of caution given the experimental nature of the various systems due for certification around mid-2014-2016.
The trio of propulsion systems – Gibraltar-based engineering operation WheelTug, Israel Aerospace Industries’ Taxibot and the Honeywell joint venture with Safran, are each vying for the attention of airlines in a bid to convince them they can secure the prize of hundreds of thousands of dollars in savings per aircraft per year.
Today’s convention sees a plethora of vehicles – and people – surround a typical push-back using a tug while current taxi to runway procedures see a Boeing 737 for example burn through 24 to 27 pounds of fuel per minute.
Clearly, component wear and the risk of foreign object ingestion is dramatically reduced with the necessity of propulsion units being dispensed with, although airlines and particularly flight crew, might question if engines would be operating as efficiently and at optimum performance if engaged only minutes before take-off.
Such concerns, however, are countered by WheelTug’s ebullient CEO, Isaiah Cox, whose company uses Airbus A320 and Boeing 737 nose-gear installed electric motors for mobility and who, as well as emphasising the cost benefits, also highlights the safety aspect of reducing jet-blast and collision incidents.
“Engines need a few, typically three minutes of warm-up and cool-down, and we budget for that,” Cox tells Air Traffic Management. “Today, many airlines do single-engine taxi already, and so it is quite common to start an engine shortly before take-off.
“The goal is to keep the engines off as long as possible, typically three minutes on each side. We are working with Eurocontrol to optimise best practices here.”
WheelTug expects certification of its design, for which six airlines including KLM, Alitalia and El Al, have inked deals for 285 aircraft, to be completed by the second quarter of next year.
“Airports are excited about WheelTug,” maintains Cox who highlighted the benefits for sites such as New York’s JFK that require aircraft to be towed to certain gates, while insisting his system could avoid the need for compensation following “million dollar accidents”, such as running into other machines.
“The safety perspective is huge,” he adds. “There are nine injuries per 1,000 jobs – people get hurt around aircraft. Jet blast from aircraft is extremely hazardous to anybody downwind – according to the Flight Safety Foundation which estimates  annual personal injury costs at US$350,000.”
Gate Operations
The WheelTug chief says pilots typically estimate the time between tower push clearance and movement at around 2.5 minutes, maintaining the same procedure with his equipment allows the flight crew to “turn on a dime – you drive out – you don’t need a push back crew – this would transform gate operations.”
Such transformation focuses on turnaround improvement that can lead to throughput improvement, although at slot-constrained airports such as London Heathrow, it is debatable whether the potential to increase traffic flow is something air traffic control would welcome, despite more precise adherence to making that slot on time being of obvious benefit.
Such a possibility does not faze Cox however. “With WheelTug you get to change ground operations, impacting safety and throughput,” he says. “If you ask a pilot how long between getting clearance for push and the aircraft moving, it is around 2.5 minutes.
“Missing your slot is always a problem but with WheelTug, the pilot has clearance from the Tower and he drives out, you don’t need a push-back crew.”
One of the other, less obvious advantages that WheelTug – and rival systems –  offer is that of environmental benefit.
“Very often, people who manage push-back are airports and airports love this idea,” says Cox. “More than anything, they love the green. If you clean up the gate area by having engines off, then you have done a lot to improve perceptions of the industry.
“If you save five or ten minutes on the turn, you see more opportunities to get more slots so the amount of work does not go down, that is huge. If every minute is worth US$66 and you only save five minutes, this is US$300 saving alone – the average margin is US$100 per flight. We are easily talking about saving per flight between US$500-US$1,000, quadrupling the advantage per airline.
Airports such as Atlanta, London Heathrow and Amsterdam’s Schiphol, could be attracted by WheelTug’s possibilities, says Cox, with them able to eliminate the frequent wait for an aircraft ahead to vacate a busy stand.
“WheelTug gets rid of that three minute delay,” he says, also citing the ability to squeeze more slots in as “curfew is defined by engine start. WheelTug invents a slot – you can’t create 15 slots out of thin air at Heathrow”.
The CEO also claims improved de-icing procedures would be possible with his system as, with the engines not running, trucks can manoeuvre around the aircraft more quickly.
Carriers could even use the system in a power-by-the-hour arrangement and therefore not have to make the capital investment, allowing WheelTug to recoup half the savings. The airline meanwhile makes money from day one.
And Cox remains upbeat concerning crew training that he estimates to be around 45 minutes. “If you can drive a golf cart, you can drive a WheelTug,” he says.
Honeywell and Safran have been working closely to develop a green taxiing system for the last two years and say the component, subsystem and system lab testing are on track, and fully-integrated, on-aircraft ground testing is expected later this year as Standard Operating Procedures are finalised.
The joint venture’s system is slated for high-cycle, narrow-body aircraft and is due to be commercially available for retrofit and forward-fit by 2016.
Honeywell and Safran have opted for mainwheel power rather than nosewheel traction as they claim less than 10 per cent of the aircraft weight is on the aircraft nose gear, making it “impossible to achieve taxi performance and system availability the airlines will require”.
One of the duo’s key arguments is that the performance of a main wheel-based system is superior – in particular in contaminated taxiway conditions such as those adversely affected by rain and ice – where greater traction is required.
They do concede this results in a “small weight increase,” but say airlines should be able to realise savings of up to 4 per cent total block fuel consumption per flight, making the extra weight economically viable, especially in high-turnaround, short haul operations.
Unlike some other systems in development, we fully integrate our system into the airframe – specifically on the mainwheel gear,” Honeywell Aerospace vice president Brian Wenig, tells Air Traffic Management.
“The Honeywell/Safran partnership combines Safran’s experience in integrated landing gear systems with Honeywell’s 40 year-plus heritage of APU innovation. Airports are excited about the benefits the system could provide them.”

“As development of the system ramps up we will be continuing to working with airports and regulators in order to define standard operating procedures for the electric green taxiing system and to ensure that aircraft equipped with the system are able to realise the traffic flow benefits the system promises” Wenig

Wenig declines to be drawn on the pricing structure of its system, but says it has received “positive feedback” from its trials with EasyJet, that has acted as a barometer for the narrowbody, fast turnaround, short haul operator, which runs multiple cycles with high taxiing volumes each day. The case for widebody is diminished, says Wenig, due to its operation of perhaps only one daily cycle.
“Other benefits include a reduction in required ground infrastructure for push-back, plus further savings in terms of reduced brake wear, extended engine life, as well as reduced carbon and other emissions and lower noise in the airport environment,” says Wenig.
“As development of the system ramps up we will be continuing to working with airports and regulators in order to define standard operating procedures for the electric green taxiing system and to ensure that aircraft equipped with the system are able to realise the traffic flow benefits the system promises.
Israel Aerospace Industries meanwhile claims its Taxibot solution is in the final stage of testing at Chateauroux airport in France, with the next step its beta test operation in Frankfurt scheduled to start in mid-2013 on Lufthansa’s Boeing 737 fleet

IAI’s Taxibot project director, Ran Braier, tells Air Traffic Management that airline testing was “excellent,” with no failures during nine demonstration runs – of one to two hours each over two weeks.
Representatives from Lufthansa – including four pilots preparing for the beta test – Air France, British Airways, United, KLM, China Eastern, China Southern, WestJet, El Al, FedEx, TCR, Bankers Capital, Charles de Gaulle and Heathrow airport – attended.
“TaxiBot is not adding any additional weight to the aircraft,” says Braier. “In fact, a significant part of the saving during taxi is burned during flight due to the extra weight of the onboard solution the aircraft needs to carry during all its flight. In addition, the driver is not saved in an onboard solution, since a technician must be on the ground to direct the pilot when he is driving backwards.
“There is no difference if this technician is in the vehicle cabin or outside – his cost is exactly the same. The real saving in fuel, FOD and CO2, is coming from the taxi and not from the pushback.”
Braier adds TaxiBot is a semi-robotic vehicle, which could be connected to the ground traffic control system. Today, many airports already have traffic optimisation software for gate holding and taxi, with this system potentially giving TaxiBot an optimal taxiing speed, through its wireless network.
IAI claims TaxiBot will maintain this speed automatically, which could create much more fluent traffic on the taxiway of major hubs.
The company started the certification process of TaxiBot last year with the FAA, EASA and Civil Aviation Authority of Israel and it expects approval for the first type of aircraft this year.
“We are in close contact with several international organisations of controllers, airports, pilots and ground handlers like ACI, IATA, IFALPA and are participating in air shows and exhibitions,” says Braier.
“But at the end of the day, it is a tailored solution for each airport which must be coordinated with each airport authority and adapted to their system.”
Despite the manufacturers’ natural optimism, it is nonetheless the airports and air traffic service providers, who will have to deal practically with such a new innovation.
German air traffic control Deutsche Flugsicherung (DFS) has been following the trials at Frankfurt Airport with interest and raises one overriding operational concern over the maintenance of acceptable taxiing speeds.
“As far as test results have been showing, it is more a question of contra-indications than advantages, which are relevant for ATC provision,” DSF spokeswoman Nanda Geelvink tells Air Traffic Management.
“When taxiing after landing with the engines off, there aren’t many problems. But using e-taxiing for push-back may present a problem if the aircraft cannot start its engines on the taxiway. Then, they would block the taxiways.”
One advantage for DFS in terms of flow management is the fact that e-taxiing can perform push-back.
“The critical question here is whether an aircraft is able to accelerate as fast as with normal taxiing and the results of the tests have been positive. The aircraft accelerated even better than with normal taxiing. The reason for that was that an engine needs about four seconds until the aircraft starts moving. Using e-taxiing, the aircraft starts immediately moving.”

Read more about E-taxi solutions in Airbus’ Fast magazine


  1. The Wheeltug system for me is number 1. Can’t wait to have this experience. What did u say – 2014?

  2. There some people who smile on WhellTug…
    Indian national hero Gandhi once said about his movement:
    First – they laugh on us.
    Than – they inore us.
    After – they fight us.
    At the end – we’ll win

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