Israel Aerospace Industries is aiming to certificate the widebody version of its pilot-controlled TaxiBot aircraft tow tractor in 2015.
Drive tests of the prototype have begun at the factory of tug manufacturer TLD near Tours in France. This is to be followed by manoeuvring trials with a trailer equipped with an original Boeing 747 nose landing gear and cockpit section as well as ballast to simulate the aircraft’s weight.
However, it is only possible to increase the trailer’s mass to around 110t, about a quarter of the maximum take-off weight of a 747-8. About 90% of the certification tests can be completed with the trailer, but a real aircraft will be required to conduct the remainder of the assessment, says IAI programme director Ran Braier.
Lufthansa – which has partnered with IAI, Airbus and TLD for the development and testing of a TaxiBot narrowbody variant at Frankfurt airport – is aiming to supply a Boeing 747-400 for the trial in 2015, says Gerhard Baumgarten, sales and marketing director at the airline’s ground handling arm, Lufthansa Engineering and Operational Services. He is also programme director for the airline’s TaxiBot introduction.
Braier expects the trial phase with the aircraft to take between four and six months. He says the programme will “hugely” benefit from experiences made with the narrowbody TaxiBot over the past year. IAI and Lufthansa have been testing the tug with a deregistered 737-500 at Frankfurt, while IAI and Airbus separately trialled a prototype with an ex-British Airways Airbus A320 at Chateauroux airport in France.
The Frankfurt test – in which several Lufthansa line pilots participated – highlighted challenges particularly with the handling when the aircraft is pulled by the tractor. At 27t, the tug was half as heavy as the aircraft. This affected the pilot’s “touch and feel” during taxiing, which should be similar to conventional ground operations when the aircraft moves under its own power.
Pilots control the Taxibot’s movement through the nose landing-gear steering tiller and aircraft brakes. But while the softness of the aircraft’s tyres effects the aircraft handling during standard taxiing – depending on speed, ground surface and weather conditions – this is different when the aircraft is pulled by the tractor. The eight wheels of the tug – all of which are motorised – provide much more grip than the aircraft’s two nose wheels, says Baumgarten.
The 737-500’s small wheel-base – the type is the smallest and lightest variant of all current- and classic-generation 737s – made the aircraft more agile during towing manoeuvres than anticipated. Pilots therefore struggled to judge the amount of steering required to conduct S-turns, says Baumgarten. He adds that using TaxiBot for other, larger aircraft will be easier.Each one of the tractor’s four wheel pairs – the widebody version has six wheel pairs – can swivel nearly 90° left and right to allow the tug to move sideways and turn on the spot. But each wheel pair swivels at a slightly different angle to facilitate the same turn radii that would be achieved if the aircraft turns with its nose wheels on the ground.
Each TaxiBot wheel pair is governed by its own control computer. If such a unit fails, the wheel pair in question should swivel freely – similar to a shopping trolley castor – and thus automatically follow the direction of the other wheels. However, that did not work as planned when Israel’s civil aviation authority assessed the vehicle for certification in Frankfurt in April.
This was part of the reason why some certification trials needed to be repeated. The last three of out of 131 test points were successfully completed during a second trial in early July, says IAI.
Approvals by Israel’s civil aviation authority and the European Aviation Safety Agency are expected to be granted by September. Lufthansa thereafter plans to assess the tractor in a six-month operational trial with scheduled 737 flights at Frankfurt.
Aside from the German airline, Braier says IAI is in discussions with several other carriers, including Air France-KLM, BA, EasyJet, Singapore Airlines and Southwest Airlines.