Airbus 320 single-engine taxi-out
On most airports (most airports I've flown to at least), you can't save 100-200kg during taxiout, since the taxi out itself will be this amount.
To save this kind of amount you would need a half hour taxi out.
Fuel consumption with both engines at idle without APU is 600kg/hour
Fuel consumption with one engine and APU is 400kg/hour. So you can save 200kg per hour, tops, assuming you taxi at idle and at the same speed (which is slightly wrong and in favor of the SETO)
So to save 100kg, with these hypotheses, you need at least a half hour taxi out.
There is no doubt I would perform a SETO with this kind of duration. But 99% of our taxi durations are below 15 min and 90% are between 9 and 12 minutes.
If you fly a very busy american airport with very long queues at the holding point, I fully understand your point. We do not encounter this situation at my airline.
To save this kind of amount you would need a half hour taxi out.
Fuel consumption with both engines at idle without APU is 600kg/hour
Fuel consumption with one engine and APU is 400kg/hour. So you can save 200kg per hour, tops, assuming you taxi at idle and at the same speed (which is slightly wrong and in favor of the SETO)
So to save 100kg, with these hypotheses, you need at least a half hour taxi out.
There is no doubt I would perform a SETO with this kind of duration. But 99% of our taxi durations are below 15 min and 90% are between 9 and 12 minutes.
If you fly a very busy american airport with very long queues at the holding point, I fully understand your point. We do not encounter this situation at my airline.
Last edited by CVividasku; 11th Apr 2024 at 16:19.
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It’s almost always worth SETO unless you’re constrained by engine warm up time, and as previous posters have pointed out if you practice it it’s not difficult.
I often start the second engine almost immediately after commencing taxi if it’s a short taxi. That reduces eng 1 run time as you’re moving during eng 2 start (assuming no atc delay prior to departure) and saves a small amount of fuel. Over a career that will be a very large amount of fuel saved.
LD
I often start the second engine almost immediately after commencing taxi if it’s a short taxi. That reduces eng 1 run time as you’re moving during eng 2 start (assuming no atc delay prior to departure) and saves a small amount of fuel. Over a career that will be a very large amount of fuel saved.
LD
With the long NEO (LEAP) engine start times I almost always start engine number two during taxi. This way, in addition to the fuel savings, I don’t waste time motoring the second engine whilst stationary going nowhere in front of the gate.
Even on smaller airports with a single taxiway and short taxi times this is worth the effort because otherwise you would be blocking the taxiway anyway. Might as well keep things moving.
I don't understand that either.
Usually, like 99% of the time, the limiting factor is the push and the towbar/towbarless disconnection.
Usually, if I wait until the ground guy says "pushback completed, set parking brake" to start the second engine (number 1 here), the engine start procedures and the thumbs up from the ground guy are obtained around the same time.
And that's with waiting. So I never lost any time by having to start both engines.
We don't have neos though
That could change the game indeed.
And I believe the neos can taxi without the APU too. That also changes a lot of things.
Usually, like 99% of the time, the limiting factor is the push and the towbar/towbarless disconnection.
Usually, if I wait until the ground guy says "pushback completed, set parking brake" to start the second engine (number 1 here), the engine start procedures and the thumbs up from the ground guy are obtained around the same time.
And that's with waiting. So I never lost any time by having to start both engines.
We don't have neos though
That could change the game indeed.
And I believe the neos can taxi without the APU too. That also changes a lot of things.
I don't know if this is an issue with the A320 series, but I know that on some Boeing types (depending on the ambient conditions), with both engines running at ground idle, you'll sometimes need to drag the brakes to keep your taxi speed down. Hard on the brakes (and sometimes noisy in the cabin - upsetting the SLF). There is an obvious advantage to single engine taxi when this happens.
That being said, as an engine guy, I want to see the engines nice and warm before setting TO thrust...
That being said, as an engine guy, I want to see the engines nice and warm before setting TO thrust...
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Usually, like 99% of the time, the limiting factor is the push and the towbar/towbarless disconnection.
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I don't know if this is an issue with the A320 series, but I know that on some Boeing types (depending on the ambient conditions), with both engines running at ground idle, you'll sometimes need to drag the brakes to keep your taxi speed down.
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I don't know if this is an issue with the A320 series, but I know that on some Boeing types (depending on the ambient conditions), with both engines running at ground idle, you'll sometimes need to drag the brakes to keep your taxi speed down. Hard on the brakes (and sometimes noisy in the cabin - upsetting the SLF). There is an obvious advantage to single engine taxi when this happens.
That being said, as an engine guy, I want to see the engines nice and warm before setting TO thrust...
That being said, as an engine guy, I want to see the engines nice and warm before setting TO thrust...
However, if the engine is truly 'cold' (i.e. shutdown for several hours), 3 minutes is pretty sporty. Especially on 'fresh' engines, 3 minutes from cold can still result in seal rubs and permanent loss of performance. If it's a quick turn-around (less than an hour), 3 minutes is fine, but not after an overnight. Of course, once an engine has a few thousand hours on it, seals and such have already been worn and this is less of a concern.
When we did high power engine runs at Boeing, it was always a minimum of 5 minutes from start to setting climb power or above.
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Adding up to the OP's question:
1. I've flown for companies that have tailored SOP, as in it's in the Normal SOP section of the FCOM and performed as a flow, from memory); companies that have additional guidance: a QRH section under the SOP tab with the entire supplementary procedure laid down and performed in read-and-do philosophy; and companies using standard, unmodified Airbus manuals.
1a. On this last company, which is the case you specifically ask for, we used to have a sort of shortened version of the SUP procedure in the normal checklist and performed it from there. As a side note, the philosophy across all 3 companies was basically the same: Aircraft on the push? PF handles the controls and starts the first engine. Aircraft under its own power? PM handles controls and starts the second engine.
2. Except for the company with the OET procedure in the Normal SOP section, in all of them, the second engine start was performed as a read-and-do procedure.
3. PF only commands the sequence of actions, i.e., orders the second engine start, the appropriate checklist to perform. No handling of the controls by the PF at any of the 3 companies.
Regarding the age old question of "just how much is worth it", I'll just add a couple of points:
Point A: Any particularly "extreme" of something, in this case application of OET in/out, (i.e, "I never do OET" / "I always do OET") is bound to have limitations, and seldomly one can argument one's such extreme point of view. The many particularities of the job we perform, not to mention the variability of said particularities on a specific day, make this kind of attitudes towards any particular decision hard to justify.
Point B: This procedure has been out there for ages now, and I feel someone, somewhere, should have picked up on something if this wasn't particularly helpful from an economic point of view. Sure, some companies operational environments may not give full benefit from this, as some other company may be greatly benefited from this. Use your head, abide by the limitations and guidelines provided by your company and the OEM and you should be fine.
I've once proposed not performing OET at an airport I usually do, being late at night, no traffic, tired from a long day and on our last sector. As an experienced aviator, we should be able to recognize the opportunities when we can (and should) perform OET. If, for any reason, we cannot, then err on the side of caution.
tdracer While I don't know if you're familiar with the A320, both the CFM56 and the IAE V2500 are equipped on other types you may be familiar with. CFM's seem to be the most rugged ones, needing only a 2 minute warm up under any case. IAE's are a bit more finnicky and do follow what you said: 2 min warm up if shut down less than 2 hours (if memory serves me right, haven't done IAE's in a while), 5 min if over 2 hours. LEAP 1A take anywhere between 1:30" to 2:30" to start (because of the dry crank before every start) and need a 3 min warmup. I'd be interested in reading your comments about any particular engine or otherwise your thoughts about this topic.
1. I've flown for companies that have tailored SOP, as in it's in the Normal SOP section of the FCOM and performed as a flow, from memory); companies that have additional guidance: a QRH section under the SOP tab with the entire supplementary procedure laid down and performed in read-and-do philosophy; and companies using standard, unmodified Airbus manuals.
1a. On this last company, which is the case you specifically ask for, we used to have a sort of shortened version of the SUP procedure in the normal checklist and performed it from there. As a side note, the philosophy across all 3 companies was basically the same: Aircraft on the push? PF handles the controls and starts the first engine. Aircraft under its own power? PM handles controls and starts the second engine.
2. Except for the company with the OET procedure in the Normal SOP section, in all of them, the second engine start was performed as a read-and-do procedure.
3. PF only commands the sequence of actions, i.e., orders the second engine start, the appropriate checklist to perform. No handling of the controls by the PF at any of the 3 companies.
Regarding the age old question of "just how much is worth it", I'll just add a couple of points:
Point A: Any particularly "extreme" of something, in this case application of OET in/out, (i.e, "I never do OET" / "I always do OET") is bound to have limitations, and seldomly one can argument one's such extreme point of view. The many particularities of the job we perform, not to mention the variability of said particularities on a specific day, make this kind of attitudes towards any particular decision hard to justify.
Point B: This procedure has been out there for ages now, and I feel someone, somewhere, should have picked up on something if this wasn't particularly helpful from an economic point of view. Sure, some companies operational environments may not give full benefit from this, as some other company may be greatly benefited from this. Use your head, abide by the limitations and guidelines provided by your company and the OEM and you should be fine.
I've once proposed not performing OET at an airport I usually do, being late at night, no traffic, tired from a long day and on our last sector. As an experienced aviator, we should be able to recognize the opportunities when we can (and should) perform OET. If, for any reason, we cannot, then err on the side of caution.
tdracer While I don't know if you're familiar with the A320, both the CFM56 and the IAE V2500 are equipped on other types you may be familiar with. CFM's seem to be the most rugged ones, needing only a 2 minute warm up under any case. IAE's are a bit more finnicky and do follow what you said: 2 min warm up if shut down less than 2 hours (if memory serves me right, haven't done IAE's in a while), 5 min if over 2 hours. LEAP 1A take anywhere between 1:30" to 2:30" to start (because of the dry crank before every start) and need a 3 min warmup. I'd be interested in reading your comments about any particular engine or otherwise your thoughts about this topic.
My airline operates in excess of 1500 sectors a day. If each sector operates most of the fuel efficient procedures, Flap 3, OETD & OETA. Taxi without APU and considered use on stand the potential savings are enormous. If you multiply a small number by a big number you get a big number.
My airline operates in excess of 1500 sectors a day. If each sector operates most of the fuel efficient procedures, Flap 3, OETD & OETA. Taxi without APU and considered use on stand the potential savings are enormous. If you multiply a small number by a big number you get a big number.
The smallest number is zero; multiply the biggest number (infinity) by this, and you get - zero!
A better rule of thumb might be "if you multiply a small number by a big number, you get a medium-sized number".
Originally Posted by PENKO
If you think that starting an engine whilst taxying is an incredible amount of workload, then I understand why you think it’s not worth it on most airports. Single engine taxi is the default in our manual. And also in my own personal preference: start one engine unless…
The more you do it, the less of a perceived additional workload it becomes.
The more you do it, the less of a perceived additional workload it becomes.
I find your remark quite silly. The workload definitely increases when performing SETO. It's not just about moving the Master Switch to ON is it? PM has to monitor the engine start AND look out during taxi, AND communicate. He then performs After Start checklist whilst dealing with yet more interruptions from ATC. PF has to stop looking out for a moment to confirm the THS setting. Flight control checks can't be done until engine has fully started and flow done. Then one finds themselves being given priority for take off and rushing through the Taxi checklist, cabin confirmation all the while with the usual interruptions from ATC. Yes, we should all find a way to manage workload but it's not all down to us is it? I'm not saying SETO is unsafe, just saying there's a time and place and you're not going to convince me that 1 minute less of Engine 2 running is worth the increase in workload. I'm interested to learn at which airports you operate from because most of the places we operate from we would be saving a minute at best.
Last edited by RudderTrimZero; 25th Apr 2024 at 07:53.
Pedantry at its finest. As it happens, the fuel savings by OETD, OETA, Config 3 etc. certainly aren't rubbish. Ask the bean counters - and every major airline that does this as a matter of course.
