Reduced engine taxi out
 

Hi,

just wondering what companies, if any have adopted the Reduced Engine Taxi Out concept onto their daily ops.

Mine is introducing the concept on all Airbus fleets.

Regards,

In my opinion, for taxi out it's a bad idea. An engine fire (uncontained) during start-up and you'll be a long way from the fire extinguisher and possibly on a congested taxiway with other aircraft either in the way, or blocking the way for the fire trucks.

Shut down an engine or two during the taxi in still has risk, but that risk is mostly confined to the probability of a tailpipe fire which can be handled by dry cranking.

Just my two pennies worth.

I'd be interested to see stats on fuel burn for this. OK, if you're going to end up in a queue for a while, I'm sure that you'll save fuel with an engine shut down.

However, if it takes (say) 3000lbs thrust to move the aircraft, you either need 2 engines producing 1500lbs each or 1 engine producing 3000lbs (prob a bit more due to the asymmetry).

I wonder what the difference in fuel burn really is (assuming no queueing)

Pappy J
 

Have to disagree with you here.

The only thing you risk is a gate return for a mechanical.

The engine fire supression systems are far better than the bottle at the gate.

If you do need a fire truck, the firemen do not need to follow the yellow lines to the aircraft and there are less obstructions on the taxiway than at a gate.

My former employer, TWA, made extensive use of this during our post bankruptcy cost control efforts. We had quite a lot of data, which, sadly, they did not think to send me prior to the merger with AA. :rolleyes: Seriously, it was standard practice even for short taxi. Our procedures were well designed and very well practiced.

In terms of fuel savings, it matters quite little for a small fleet. However, when considering a large fleet, our belief was that the small percentage of fuel saved over one year by each of several hundred daily operations could be significant.

The only safety issue that I have ever been aware of with this practice is the use of excess thrust in the ramp area. This can, of course, be very serious if you happen to be at the receiving end of the debris field. But it is easily controlled with weight limits, N1 limits and a smattering of good judgement.

Boeing, naturally, discourages this practice, but I really don't think there is any basis for this other than not-invented-here syndrome.

Saved 500kg & 240kg on last 2 deps from NYC. Go do the maths. ;-)

Olepilot,
Interesting - Could you give us some more info? Aircraft type and how much time was spent stationary.

Cheers

At my place I try to taxi on two engines if weight plus other conditions allow it. It not only saves fuel but about one minute in time for each aircraft departing. When 120 aircraft are departing and 60 can start the last engine during the taxi 60 minutes are saved at a reported $1000 per minute. That savings does not count the cost of the fuel saved. MD11/MD10

On the 727 we would start all three, taxi from the apron, and once on the taxi-way... shut down number 3. In some cases, when we were below 150,000 (68 tons) we would shut down two and three, and use the APU for electrics and Air conditioning. Saved alot of fuel at KJFK during the big push hours:ok:.

captjns
 

I'm having a hard time working out the logic of starting them at the gate then shutting them down again. Could you enlighten me?

Hi,

Depending on aircraft weight and apron slope, on the TriStar, we'd start 2 or sometimes all 3, then during the prolonged taxi queues (JFK especially), we'd taxi on two engines (and shut the 3rd one down if started).

We used to get lousy mpg with 3 idling engines and the parking brake set.

But that was in the early 80s, now we are "catching up" again and doing it on A319 - 20s.

Idle fuel flow on a 737NG is around 400kg/hour/eng. Most of that (at ground idle) is used just keeping the fire going, and the metal spinning rather than producing useful thrust, so you can reduce your taxi fuel burn by about 40% by shutting down/not starting an engine.

A short, 10 minute taxi thus saves around 30 kg (round figures = £20), which doesn't sound much, but with a fleet of 100 aircraft, flying an average of 4 sectors each, 365 days per year this = nearly £3 million! Save fuel on a 20 or 30 minute taxi and you are really saving cash.

In terms of Risk Assessment - starting the second engine on the move is a crew distraction which needs to be managed with solid procedures. The fire risk is the same (i.e. negligible) and the evac/fire engine access is probably better on a taxiway than on stand - given the better access to the aircraft and clear area for the slides.

The difference between Boeing & Airbus is that the Airbus start and abnormal-start shutdown is more automated (read, less chance of damaging an engine whilst distracted) than the Boeing.

@welliewanger

330 in NYC. but we do it on the 340 also.
Had some 15 acft ahead of us on the first and only a few on the latest

captjns:For most engines, shutting down & re-starting counts as an extra Low Cycle Fatigue (LCF) cycle on rotating parts. These life-limited parts must be scrapped after a FAA-prescribed number of cycles. :eek:

Unless your carrier has some special dispensation about starting to only idle N2, and counting this as a partial LCF cycle, this practice can be false economy in a BIG way. Check with your engineering department!

I also do not see the logic in shutting down #3 engine first when #2 has a whole lot less responsibility on this type.

We used to taxi the A320 in and out on one, but not the Boeings, but I think that changed after I left. SE taxi in was actually much easier on the 319 because it needed much breaking.

We taxi in and out single engine as often as is practical. The saving on my aircraft is about 5kgs per minute which on the face of it is not much, but over a year this comes to very big bickies.

PM

single engine taxi on an airliner.. :ugh:
..just unprofessional, bean-counter bull..:mad:
..but obviously we work like monkeys...they order us to land on foggy airports....they order us to do single engine taxi....what is coming next...maybe shut down one engine on the TOD...tell the bean-counters to not do flying..this saves fuel, saves money for catering, saves expenses for maintenance, save, save:yuk::yuk:

Otherwise -

Rated thrust for all ops, full reverse all landings, MCT cruise, spend$$$, spend$$$ till your competitors have you for lunch. :rolleyes:

To those involved: do you keep your APU running to start-up the other engine or rather perform a cross-bleed start?