Tugs versus aircraft engines: a ground handling question

[ross_M]

A possibly naive question: Since aircraft jet engines are fuel guzzlers and terribly expensive to idle away on the ground is it an option to use ground tugs all the way till the runway on departure?

I'm not sure what the economics are but I guess it is a question whether the capital investment in a tug is worth the fuel saved while idling? Besides the lower fuel consumption I suppose tugs are more amenable to a stop-start operation if the conditions so demand.

Technically though, present-day tugs seem maneuverable and powerful enough, for this op. right? Maybe the top speed would be too low? Any other problems?

Or maybe this option has already been tried before....

[ExXB]

I think the 'bearded one' made an announcement that VS was going to tow their aircraft to the runway to save fuel.

Never came about though. Apparently towing a fully laden (fuel, passengers, freight) aircraft is not the same as towing a (mostly) empty one. More than twice the weight and inertia! Also, apparently, the strain on the landing gear - which was not designed for fully laden towing - causes issues which offset any savings.

[PAXboy]

This question should be in the history somewhere as I recall a fairly long discussion with a lot of points, not just the main ones that ExXB so helpfully listed.

You can be sure that, if it would save money (short or long term) it would have been done! A similar point is about tyre wear when the wheels spin up on touch down and the benefits of spinning the wheels up before hand. It has been tried and found to be of no financial benefit, but it is interesting if you can find the thread/s.

[G&T ice n slice]

I have a vague recollection of a fully laden 747 having to shut down engines & be towed back to the ramp.

unfortunately after about a mile there was a 'bang' from the tug & clouds of black smoke followed by the tug driver bailing out.

Just cann't remember where & when (or, indeed why, or who, or what)

[ross_M]

This question should be in the history somewhere as I recall a fairly long discussion with a lot of points, not just the main ones that ExXB so helpfully listed.


This one might be a similar thread; it talks about an APU powered motorized nosewheel (http://www.pprune.org/archive/index.php/t-298722.html)

Is Delta still using this?

Also, apparently, the strain on the landing gear - which was not designed for fully laden towing - causes issues which offset any savings.

Is it possible to tug but not via the landing gear? Is there a possibility to have some sort of attachment points or pulling lugs? I guess that's for the designers of the future though.

[PAXboy]

If you strengthen an area of the underside, that could then take the strain of a new kind of towbar, the weight that it would add to the a/c would be significant. That strengthening would have to be airlifted every inch of the way as dead weight.

Then you have to have all the destinations able to handle the new tow bars and weights. Then have the new vehicles and the extra staff to drive them. ALL of that cost will be handed back to the airline by the airports. So, you might as well just drive the a/c to the end of the runway as you are then in charge of all the costs (fuel/time).

Imagine the fun if someone was all closed up and ready to go 14hrs - but the tug was delayed because of no manpower or a breakdown or another a/c was delayed and so the tug is still at the wrong end of the field? No carrier wants that.

[RevMan2]

Towbar-less tractor from Goldhofer currently in use with a LH Technik subsidiary surrounds the nosewheel, picks it up and taxies at high speed
AST-1X Aircraft Tractor from Goldhofer Aktiengesellschaft (http://directory.groundsupportworldwide.com/product/10025932/Goldhofer_Aktiengesellschaft_AST-1X_Aircraft_Tractor)

[ExXB]

Towbar-less tractor from Goldhofer currently in use with a LH Technik subsidiary surrounds the nosewheel, picks it up and taxies at high speed
AST-1X Aircraft Tractor from Goldhofer Aktiengesellschaft (http://directory.groundsupportworldwide.com/product/10025932/Goldhofer_Aktiengesellschaft_AST-1X_Aircraft_Tractor)

These lifter/draggers have many benefits, unfortunately these don't include reducing the strain on the landing gear when towing a fully loaded aircraft. Eventually something breaks, and that is expensive (in time and money).

[Hipennine]

Apart from some engines actually needing run-up times to optimum temparatures, etc., I would imagine that:

1/ the capital cost of a huge fleet of sufficiently powerful tugs,, their fuel cost, and tyres cost (which could be quite substantial),
2/ the capital and practicality of a largely seperate taxiway network for these things to travel on when not actually towing acraft (and the associated ground control conflicts, and,
3/ the salary cost of a hugely expanded cadre of highly trained drivers (with responsibility for the lives of thousands of pax, and bla, bla), plus whatever the practical solution is to replace the ground based walker with the comms to the flight deck,

would all contribute to this being a non-starter.

[Truck2005]

At the airfield I work at they have fairly recently installed new ILS masts. Unfortunately, one of them has changed the taxi pattern due to the fact that the most common a/c that use the field have a wing span larger that the clearance to the mast. This involves the aircraft being pushed back down the runway, depending on runway in use. This means that slot times have to be borne in mind when flight planning, (in this case an extra 30 minutes)!
With everything weighed up a 1 - 2 tonne fuel penalty, (depending on flight planned fuel burn), most probably is the cheaper option.

[SassyPilotsWife]

While I'm no expert at all, I have worked on the ramp for 2 airlines of which one is probably the busiest and extremely dangerous on a Saturday night. I cannot picture the FAA allowing tugs to the runway with the exception of a distressed a/c needing to be brought to the gate. Safety is probably the biggest reason not to do this. Too much traffic to include not only other a/c, but also emergency vehicles, mx, etc.. in between the rwy and apron. Don't let the bean counters remotely think of this to save fuel. Because they surely would LOL

[sunnybunny]

I did ask a captain this on a flight once some years ago (in mid flight whilst waiting for the loo to become free). He suggested the cost of hiring the tug etc. was more than the fuel cost so wasn't cost effective.

Out of curiosity on my recent holiday the aircraft had to be pushed back at BHX but at Almeria LEI the aircraft were parked so they could just turn and go which neccessitated steps being bought out. (Some smaller aircraft had their own).

So which costs more? bringing steps out or pushing with a tug? Or is it airport dependant?

[surely not]

It is a question of how busy the airport is. If it is relatively quiet with a gentle peak with no pressure on stands required then self manouevring is possible.

If it is a busy airport with a high density peak needing as many stands as possible then nose in and push back out maximises the number of aircraft that can be accepted in any period of time.

[Anagram]

I saw a BA 747 being towed down one of the taxiways at LHR lately, and it was s-l-o-w. So that's probably one reason.

[Peter47]

The process is likely to be more economical for larger aircraft as one tug and driver is required whatever the size. (I am assuming that the a/c would be under the control of the flight crew which would handle radio comms so towing could be done with one driver.) Obviously the greatest savings would be where there are long taxis and waits - JFK, LHR, FRA come to mind. Presumably engines would be started up shortly before take off and the aircraft would taxi onto the runway under its own power. I have experienced some very short taxi outs in my time (DL at MIA and BWI come to mind.) A hot start could give ATC headaches though!

I understand that a 747 can burn over 1 tonne in a 30+ minute taxi at an airport like JFK - thats around $1,000 so we are not talking peanuts.

One advantage is that you have the back up of a conventional taxi if you run short of tugs so you don't need a lot of contigency equipment lying around.

As we know Boeing is not keen about fully loaded aircraft being towed at speed (and I presume also Airbus).

I have seen it suggested that lighter aircraft where towing would not be economic could have an electric motor fitted to the nose wheel which could be powered from the APU. This would also avoid the need for a push back although of course, one or more wingmen would still be required, plus I would imagine, a camera in the tail.

Two questions for pilots? I know from my father who used to be a pilot (many years ago) that there was always an engineer around when winding up an engine. I presume that now that engines are far more reliable and routinely shut down in remote holds, that this is no longer required?

Also what is the minimum time it would take to light up your complement of engines and do do all your checks to be ready for take off?

Plus a couple for engineers. What would the weight penalty be of
a) strengthening nose wheels to permit high speed towing and
b) installing an electrical drive system powered from the APU?

[hellsbrink]

I saw a BA 747 being towed down one of the taxiways at LHR lately, and it was s-l-o-w. So that's probably one reason.

That would be because of the speed limits imposed on ground vehicles, even on taxiways (unless it's an emergency, of course), although I have seen tugs doing a bit more than their limit whilst towing, especially at night when the place is closed, and that can kinda put the willies up ya when you see a tug towing something past you at that sort of speed. Let's put it this way, if something happened they would never stop in time.

[FlyingEagle21]

Ross M: Is it possible to tug but not via the landing gear? Is there a possibility to have some sort of attachment points or pulling lugs? I guess that's for the designers of the future though.

Short Answer: No.

Reason being the landing gear steering is disconnected (no flight deck control) when an aircraft is being towed and therefore if the tug is not connected to the gear, it cannot move. Even if it is not disconnected you can't really have the nose gear moving independently from the tug.

[PAXboy]

You can be sure that, all of these things have been rigourously investigated by all interested parties. If it would save money (short or long term) it would have been done!

Another point that has been aired here before is that, if an a/c is towed and then has to do a remote start - you need a 'lay by' for it to do so. They would have to be constructed and many airports don't have the spare space to build them. If the a/c fails to start - or some other failure - you then have to get it towed back to the gate. Since the taxiway will be full of other a/c being towed out - you would have to tow it down the runway. At 10mph (or whatever) how many slots would that take up?

Lastly, on the electrical motor thing, the previous thread said:


You need a whacking great motor to haul 250 tons
To carry that motor to your destination will mean many less pax carried



So do you drop the motor off at the start of the runway? If so, then they have to be got back to the starting point again.

If you want to save pointless fuel burn - get the UK govt to put a third runway into LHR and a second into LGW so that no one has to stack. THAT's the one that everyone wants to fix. but this thread is NOT about that! :ooh: