I have seen this subject debated several times in various forums here. The main points against are (as I recall):
- If the tug is not available when the a/c is ready for push - the airport gets the blame. If they miss their slot?
- The numbers of tugs needed for peak time would be very high - because you have to allow for the long return trip to the terminal area to collect the next. Thus you would have to have many tugs sitting around in low periods.
- How does the tug get back to the terimal? taxiways are one way and unless there is an easy route back, a new tug track would have to be laid and some places would not have space for that.
- So the tug gets the a/c to the start up bay: Should it wait until the start is complete, or just go? If the start cannot be completed, how do you get the a/c back to the terminal? It would have to go onto the runway and off at the first exit. Failed starts are few these days but the busier the field, the greater number of problems in a year. Anyone fancy a failed start blocking one of LHRs two?
The next big discussion point has been: Wear and tear on the a/c.
- The nose wheel is designed to handle the weight to the tug or to hold the weight on a lift up tug. Manufacturers have said (I read) that they are not sure about the extra strain on regular towing, much more than the towing for maintenance. So the nose gear might have to be strengthened = weight.
- The idea of electric motors (donkey engine) attached to the nose gear was (I read) tried but the weight of the required powerful motor meant that it was not cost effective to take it with you. So you have to have folks disconnecting and collecting the donkey motors at the start point and returning them to the terminal.
- So - what speed limits would there be for towing or the donkey engine?
- Will you have enough of the right types of donkey motors for the number of departures and types you have that day?
You would just have to start in the normal way if:
- No tug available
- No tug staff available
- No donkey available
- No staff available to mount/remove donkey
Accordingly, depending on which way you look at it, this method could work better for small regional fields with not many rotations and small delays not a problem. Or, the big hubs, because there are more movements and so the potential savings are great. But, of course, the potential delays are greater.