In a 15-minute taxi between gate and runway, a Boeing 747 can burn about a tonne of fuel.
At current prices that fuel costs around $680. While aircraft jet engines are very efficient in propelling an aircraft when airborne, performance suffers when pushing that mass around on the ground.
So why not use a tow vehicle similar to the ones that are used to push aircraft away from the gate?
One reason is that these vehicles lack sufficient power to move a fully loaded A380 or 747 at reasonable speed, another is that jet engines need to warm up before takeoff, and finally pilots greatly prefer to be in charge of their aircraft's movements.
One solution is TaxiBot, a powerful, semi-robotic, pilot-controlled vehicle which transports aircraft from terminal gates to the runway and back, with the aircraft's engines set to idle. TaxiBot has been in operation towing Lufthansa's Boeing 737 aircraft at Frankfurt Airport since 2014, saving around 11,000 tonnes of fuel a year.
Certification was recently extended to include all Airbus 318, 319, 320 and 321 aircraft, including the NEO variants.