At some airports in Europe and the USA, tow-barless tractors have replaced many of the conventional tugs used for moving aircraft. They are particularly efficient in towing aircraft between docking points and hangars or engineering areas, because they can do so at taxiing speed without needing a crew on board the aircraft or any power source - even batteries - switched on in the aircraft. This eliminates the need to carry skilled personnel in the flightdeck.
Where conventional tow bars have proved to be vulnerable to fracture and provide tractor drivers with only limited control over the towed or pushed aircraft because of the two-point linkage between the aircraft and vehicle, tow-barless tractors take more direct control of the aircraft. They do this with a hydro-mechanical clamp system which grabs the nosewheel fore and aft and lifts it just clear of the ground. With the aircraft's nosewheel steering disconnected so that the nosewheel pivots freely, the tractor and aircraft effectively become a single articulated vehicle with all the control - steering and braking - in the tractor. Lighting for movement at night can be provided by floodlighting or strobing the aircraft from the tractor.
The tow-barless tractors are relatively expensive, which is why Frankfurt Airport says it is keeping conventional tugs for simple pushbacks from stands. At the same airport, however, Lufthansa Engineering and Operational Services (LEOS) uses them for positioning aircraft because it frees skilled personnel from having to crew non-operational aircraft. LEOS says they can tow the aircraft safely at more than 30km/h (18mph) compared with tow bar tugs which are restricted to about 10km/h. UK-based tug manufacturer Douglas sells its larger tow-barless vehicles for about $1 million a unit, and LEOS uses German made Krauss-Maffei, Goldhofer or MAN tugs.
Three years of UK Civil Aviation Authority tests, in co-operation with British Airways, which operates 17 Douglas tow-barless tugs, have been extended. The operation of the vehicles is no longer in question, but tests on external lighting for visibility during night movement have yet to be finalised.
Source: Flight International
