i) I would like to know how much time does it take to engage and disengage the tugs to the aircrafts with Towbar and Towbarless Tugs to push and tow.
ii) What is the maximum speed towing an aircraft?
iii) Does it depend on the aircraft weight, type?
iv) Does it exist electric or alternative fuel tugs for aircrafts?
Anything from 2-3 mins to 15 mins!
Question iii first: yes, it does very much depend upon aircraft weight (mass) and type. It also depends upon whether or not you are towing empty from a stand to a hangar or remote parking spot, or pushing back a 'live' aircraft for departure, or using a traditional tug with bar or a newer towbarless type.
Queston i. A fully laden 747 will normally take 5 - 10 mins from start of push to being able to taxy. One engine is usually started using the APU as teh push starts, then another as the aircraft is almost on the taxiway centreline. A third and then the final engine are started after the park brake has been re-applied to allow the tug to disconnect. This procedure can take up to 10 mins depending upon issues on startup. After disconnect, the tug has the towbar re-attached to it and moves well out of the way. The headset person will then remove the nose steering pin, walk to the side of the aircraft and hold the pin up so that the flight deck crew can see it. This is their signal that it is all clear to contact ATC for taxy instructions. A towbarless tug can achieve this slightly more quickly, but the key really is the time taken to get the engines started and the headset person to check all is well under and behind the a/c. A smaller aircraft, such as the B737 or A320 is more easily manoeuvred with a towbarless tug than a tug and bar. A towbarless tug pushback can potentially be operated by a single person as the tug driver has a good view under the a/c for advising the flight deck of what's going on behind them but with larger aircraft the wingtips can't be easily seen and additional wing-walker personnel are an essential safety feature. Some airlines pay their Handling Agent specifically to provide this; as a result of seeing the expensive consequences of bashing wingtips into vehicles, structures and other aircraft, no doubt!
ii Maximum Speed. Some trials with extended towing of a laden B747 last year were limited to 4kt (about 6 kmph) to avoid possible strain on the nose leg. Empty B737 can be towed at over 20kt (30+kmph) with a towbarless tug, in a straight line. However, I have attended 2 jacknife incidents involving towbarless tugs where towing speeds on a turn might have been a factor. They can also be pushed back empty quite quickly so can catch people at the back of stands un-awares - hence the need for wingwalkers again. Tugs with a separate bar are often nnot able to do more than 15kmph, even without anything to tow.
iv. I've operated electrically powered tugs for small aircraft, but once you move up to the bigger vehicles, I doubt if you could provide sufficient power with batteries. A B747 tug can weigh as much as 70 tonnes, after all, it's pushing 400 tonnes, often on a wet, greasy surface. All the bigger tugs run on diesel and all things considered, there probably isn't a huge environmental saving for the effort involved in electrifying them. There are much greater benefits going for electric baggage vehicles, dispatchers cars etc. Geneva airport even provide a bicycle for dispatchers, can't get more environmentally friendly than that!
Cheers,
TheOddOne