Do pilots ever taxi out to the runway on just 1 engine starting the other engine just before it is there turn to takeoff? On a recent flight on a B717 I could not see either of the engines but based on sound I think that is what they did. I could hear the APU start before we pushed back, after push back I could hear the airflow change and the spool up sound of engine start. We taxied out and waited in line for 5-10min then when we were almost up I heard the airflow change and the engine spool up sound again. Is this common? Is there a different explanation for what I heard?

Single engine taxi is a pretty routine procedure in all but the largest twins. Hard to say what you heard in the 717, as it has by far the noisiest cabin since the demise of the BA146.

Did it on the ATR, A320 and eve A330. Having said that, single engine taxi out is not very common and many airlines don't authorize it, as there can be several problems. Single engine taxi in is much more common....

In a previous life at a regional airline single engine taxi in/out was standard operating procedure. Unless the taxiways were contaminated the RJ did just fine taxiing around on a single engine. With my current airline we are able single engine taxi but it is definitely not standard procedure, there are many restrictions (including maximum weights) and most of the time it’s not worth the headache to save a small amount of fuel.

Tn55337 wrote:

Do pilots ever taxi out to the runway on just 1 engine starting the other engine just before it is there turn to takeoff? On a recent flight on a B717 I could not see either of the engines but based on sound I think that is what they did. I could hear the APU start before we pushed back, after push back I could hear the airflow change and the spool up sound of engine start. We taxied out and waited in line for 5-10min then when we were almost up I heard the airflow change and the engine spool up sound again. Is this common? Is there a different explanation for what I heard?

For us, single engine taxi is highly recommended and often used. When we do transcons flying out of JFK, we can experience massive 1+ hr taxi delays so single engine taxis save enough fuel to prevent a return to gate.

Unless we are really heavy in a 321, maybe even a 320, I generally do a single engine taxi out if it's dry out. Just need to plan on getting the required warm up in before takeoff. Our warm up is 3 minutes unless it's been shut down more than 2 hours, then it's 5 minutes.

Taxi in, after an idle reverse landing we can shut one down right away.

thepinkmachine wrote:

Did it on the ATR, A320 and eve A330. Having said that, single engine taxi out is not very common and many airlines don't authorize it, as there can be several problems. Single engine taxi in is much more common....

Load and conditions permitting or course, we were encouraged to taxi out single engine and did so in 737s and 757s, but not 767s. Also, we did taxi on 2 engines on the 727. Seems like single taxi out was common in the regional turboprops, too - I distinctly remember a woman who was concerned about the stationary prop one time.

Taxi in single engine was even more common.

As the price of fuel increases, I'd expect more focus on single engine taxiing again.

Single engine taxi in didn't work out too well for an NWA DC-9 crew

https://aviation-safety.net/database/re ... 20050510-1

On my recent intra-european flights, single engine taxi in and out is becoming quite routine, almost a non-event. Much more frequent than say 5 or 10 years ago. I suppose cost and environmental considerations have a much bigger say than before.

Regards..

B8887

Back in 2007, I flew two Delta Boeing 757-200s. One from JFK to SLC, the other from SLC to ANC. Both did single-engine taxis. In the case of JFK, we were stuck in a long taxi line for 31L, so the second engine wasn't started until we were sitting on 22L.

Back in the day, I worked at an MRO and our hot shot engine run guy was taxiing a 727 back to the hanger after doing an engine run. They had done some ground tests and left the hydraulic ground interconnect valve closed. As they were approaching the hanger he shut down engines 2 and 3 (engine 1 has no hydraulic pump). Fortunately. the tug with the tow bar that was used for push back was sitting in front of the hanger and he managed to stop the airplane by straddling the tow bar with the nose gear tires.

Happened to me as well… When I was a brand new F/O on the ATR, one idiot captain decided to cut both engines when entering the parking stand with the intent of coasting into the final parking position.


It went pear-shaped when he tried to stop the plane and discovered the brakes were not working... Fortunately the parking brake was still operational and saved the day.

In his defence: "it sounded like a great idea at the time..."

Not an expert on this topic but is it possible (or a risk) to be out in the taxi que and the second engine not start?

dfwjim1 wrote:

Not an expert on this topic but is it possible (or a risk) to be out in the taxi que and the second engine not start?

I would think if that happened, you'd just return to the gate. Probably wouldn't be much different than if you had started the second engine after pushback.

dfwjim1 wrote:

Not an expert on this topic but is it possible (or a risk) to be out in the taxi que and the second engine not start?

Of course that could happen. There are other risks with single engine taxi out also. What if you have a tailpipe fire when you start the second engine? You don't have your ground crew nearby to assist (tailpipe fires are not detected by the engine fire detection system).

What if ATC clears you to jump ahead in line and takeoff immediately but your second engine isn't started?

One airline blew a baggage cart into an employee because breakaway power from the gate with only one engine was so high. Another airline had a very near miss on a taxi way because one pilot had his head down starting the second engine.

Some airlines are choosing to live with the risks and do it because they believe it saves fuel.

For these various reasons, Boeing used to provide guidance to the customers prohibiting single engine taxi out. Taxi in was okay in certain cases - having adequate warm down time, etc.

Some airlines like DL said too bad, they are going to do it anyway. Other airlines wanted to do it and asked Boeing to soften that guidance so their own regulatory agencies would permit them to do it. Boeing then figured that the customers are big boys and if they chose to do it, there is no reason to prohibit it. Now technical guidance is provided to the customers of the airplane system effects of doing single engine taxi. The customers can decide if it fits in their operational environment and adopt the safest possible procedures to do so.

Did two engine and even one engine taxi at light enough weights on the B727


Same on the -80


For years we did not do SE taxi on the 757 / 67, now it’s approved but I never saw the point, it’s hard on the nosewheel and any fuel savings is gone when you have to use excess SE thrust to start rolling once you’ve stopped

Not to mention who you’re blowing away behind you

BoeingGuy wrote:

dfwjim1 wrote:

Not an expert on this topic but is it possible (or a risk) to be out in the taxi que and the second engine not start?

Of course that could happen. There are other risks with single engine taxi out also. What if you have a tailpipe fire when you start the second engine? You don't have your ground crew nearby to assist (tailpipe fires are not detected by the engine fire detection system).

What if ATC clears you to jump ahead in line and takeoff immediately but your second engine isn't started?

One airline blew a baggage cart into an employee because breakaway power from the gate with only one engine was so high. Another airline had a very near miss on a taxi way because one pilot had his head down starting the second engine.

Some airlines are choosing to live with the risks and do it because they believe it saves fuel.

For these various reasons, Boeing used to provide guidance to the customers prohibiting single engine taxi out. Taxi in was okay in certain cases - having adequate warm down time, etc.

Some airlines like DL said too bad, they are going to do it anyway. Other airlines wanted to do it and asked Boeing to soften that guidance so their own regulatory agencies would permit them to do it. Boeing then figured that the customers are big boys and if they chose to do it, there is no reason to prohibit it. Now technical guidance is provided to the customers of the airplane system effects of doing single engine taxi. The customers can decide if it fits in their operational environment and adopt the safest possible procedures to do so.

• Tailpipe fires are not a big deal... they extinguish on their own. However, there are OTHER uncontained fire types and having no immediate fire fighting could be a big problem. This is a risk airlines are taking on your behalf. You are correct in that there is the assumption that fire detection systems work and that fire suppression systems likewise put the fire out. Lastly, there is the presumption that airport firefighters can get there quick enough and that people can evacuate these ultra-high density loads in the event of a fire that won't go out. Your concern is very legitimate: https://en.wikipedia.org/wiki/British_A ... Flight_28M
  Thank you federal government (FAA) for proving once again that safety is not the most important thing.
• If ATC clears you jump into an intersection to skip ahead, you just have to communicate your limitation. Most all new designs require an engine warmup time that can be upwards of 5 minutes at Idle thrust. Pilots have to use their experience to decide when to start the second engine for scenarios like this.
• Taxiing incidents are certainly a big risk. This is a glaring safety issue that the FAA will not address because the airlines don't want to.
• Airlines live with TONS of risks because it doesn't cost them anything. The regulatory requirements are not very high. Plus, in order to win in court, you have to prove things while fighting high paid corporate lawyers. The burden of proof standard is not the problem. The problem is that it's up to you to gather the evidence to make your case. Good luck getting company proprietary data. Look up Aerotoxic Syndrome ( https://en.wikipedia.org/wiki/Aerotoxic_syndrome) and you'll see something that affects the entire industry yet lawsuits have been unsuccessful. It's an uphill battle like proving that smoking is unhealthy. There have been some industry successes (elsewhere) such as a gardener winning against Monsanto because he got terminal cancer. https://www.cbc.ca/news/health/monsanto-payment-cancer-roundup-1.4781751

Taxiing single engine does save fuel. We do that sometimes when our minimum takeoff fuel is very close to our fuel loadout particularly at airports where taxi times can exceed 1 hour.

The FAA has absolutely no rules preventing the practice. I don't really think they should but there certainly are some risks involved. I'm fairly neutral on whether this is good or bad overall but there certainly are some issues with it.

dfwjim1 wrote:

Not an expert on this topic but is it possible (or a risk) to be out in the taxi que and the second engine not start?

Well, when you are say less than 1000 to 500 feet from the hanger and you realize that you have no brakes there isn't time for much of anything except to brace for impact. They didn't even have time to use the emergency airbrakes that the 707 and 727 have. The best scenario would have been to open the hydraulic ground interconnect valve and the AC hydraulic pumps would have stopped the aircraft.

greendot wrote:

BoeingGuy wrote:

dfwjim1 wrote:

Not an expert on this topic but is it possible (or a risk) to be out in the taxi que and the second engine not start?

Of course that could happen. There are other risks with single engine taxi out also. What if you have a tailpipe fire when you start the second engine? You don't have your ground crew nearby to assist (tailpipe fires are not detected by the engine fire detection system).

What if ATC clears you to jump ahead in line and takeoff immediately but your second engine isn't started?

One airline blew a baggage cart into an employee because breakaway power from the gate with only one engine was so high. Another airline had a very near miss on a taxi way because one pilot had his head down starting the second engine.

Some airlines are choosing to live with the risks and do it because they believe it saves fuel.

For these various reasons, Boeing used to provide guidance to the customers prohibiting single engine taxi out. Taxi in was okay in certain cases - having adequate warm down time, etc.

Some airlines like DL said too bad, they are going to do it anyway. Other airlines wanted to do it and asked Boeing to soften that guidance so their own regulatory agencies would permit them to do it. Boeing then figured that the customers are big boys and if they chose to do it, there is no reason to prohibit it. Now technical guidance is provided to the customers of the airplane system effects of doing single engine taxi. The customers can decide if it fits in their operational environment and adopt the safest possible procedures to do so.

• Tailpipe fires are not a big deal... they extinguish on their own. However, there are OTHER uncontained fire types and having no immediate fire fighting could be a big problem. This is a risk airlines are taking on your behalf. You are correct in that there is the assumption that fire detection systems work and that fire suppression systems likewise put the fire out. Lastly, there is the presumption that airport firefighters can get there quick enough and that people can evacuate these ultra-high density loads in the event of a fire that won't go out. Your concern is very legitimate: https://en.wikipedia.org/wiki/British_A ... Flight_28M
  Thank you federal government (FAA) for proving once again that safety is not the most important thing.
• If ATC clears you jump into an intersection to skip ahead, you just have to communicate your limitation. Most all new designs require an engine warmup time that can be upwards of 5 minutes at Idle thrust. Pilots have to use their experience to decide when to start the second engine for scenarios like this.
• Taxiing incidents are certainly a big risk. This is a glaring safety issue that the FAA will not address because the airlines don't want to.
• Airlines live with TONS of risks because it doesn't cost them anything. The regulatory requirements are not very high. Plus, in order to win in court, you have to prove things while fighting high paid corporate lawyers. The burden of proof standard is not the problem. The problem is that it's up to you to gather the evidence to make your case. Good luck getting company proprietary data. Look up Aerotoxic Syndrome ( https://en.wikipedia.org/wiki/Aerotoxic_syndrome) and you'll see something that affects the entire industry yet lawsuits have been unsuccessful. It's an uphill battle like proving that smoking is unhealthy. There have been some industry successes (elsewhere) such as a gardener winning against Monsanto because he got terminal cancer. https://www.cbc.ca/news/health/monsanto-payment-cancer-roundup-1.4781751

Taxiing single engine does save fuel. We do that sometimes when our minimum takeoff fuel is very close to our fuel loadout particularly at airports where taxi times can exceed 1 hour.

The FAA has absolutely no rules preventing the practice. I don't really think they should but there certainly are some risks involved. I'm fairly neutral on whether this is good or bad overall but there certainly are some issues with it.

A lot of assumptions not based in fact. How exactly is a delayed engine start higher risk than an engine start at push back? It isn't. The fire suppression system does absolutely nothing for core fires while a fire in the fire suppression zones could happen even in flight. So should we have a firetruck fly with the aircraft? I guess that would satisfy your assumption of required safety procedures.

Starlionblue wrote:

Max Q wrote:

Did two engine and even one engine taxi at light enough weights on the B727


Same on the -80


For years we did not do SE taxi on the 757 / 67, now it’s approved but I never saw the point, it’s hard on the nosewheel and any fuel savings is gone when you have to use excess SE thrust to start rolling once you’ve stopped

Not to mention who you’re blowing away behind you

The extra burn from higher thrust is apparently more than covered by the savings of only having one engine running. At least according to our fleet management. And they certainly wouldn't be encouraging it if it didn't save money. They even publish savings figures per fleet due to RETI.

It isn't just fuel. If you're paying "power by the hour", every minute counts.

I can guess which carrier Max Q flew for. There was one prominent US carried that believed their calculations showed that single engine taxi was not a fuel saver due to the higher thrust the other engine is sometimes run at. It’s even less savings if the APU is running, which Boeing recommends.

Just to add that I'm pretty sure I already saw an airline bragging about SET in an inflight magazine if I'm not mistaken. Not sure which one, possibly U2, and this was easily like 5 years ago, not 5 months ago.

Starlionblue wrote:

They even publish savings figures per fleet due to RETI.

Correct. I separately saw the figures in annual savings in fuel and CO2 emissions for an average airline, and although not in the millions, it can easily reach the the six-figure amounts. Pretty significative I would say.

Regards.

B8887

I don’t see what the big deal is with single engine taxi. You guys are making it out to be way harder then it is. Does it save fuel? Yes, certainly it does in many circumstances. Every, and I mean every single airline in the USA has a single engine taxi program. There is a little to no risk in single engine taxiing as long as you are patient with break away thrust.

Some comments to address....

What happens if the other motor doesn’t start: well, you have a lot bigger problem on your hands potentially, and are likely doing a gate return.

What happens if they tell you to skip then line? Well, you tell them you aren’t ready.

You don’t single engine taxi at BDL or PBI, you do single engine taxi at LGA and JFK. It’s all situational and can save an airline millions annually on their fuel bill.

At my airline, an airbus operator, single engine out is FAR more common then in. In order to single engine taxi in you need to have the APU running on the a320 series. If you have a sub 5 minute taxi what’s the point in wasting an apu start cycle to single engine in. Just pull into the gate with 2 running and shut #2 down once chalked, #1 after being plugged into a GPU.

I’ve never had an issue taxiing on one engine and I’ve never seen anyone else have an issue, save for when they’re suddenly number one and need a few minutes to warm it up. It’s such a routine, not-at-all-an-issue thing that I’m kinda surprised at the length of some of these negative replies.

Taxiing in on 1 is less common simply because, once on the ground, you care a lot less about fuel, your taxi time tends to be much quicker, and also there’s a time limitation on many aircraft for shutting engines down after landing. It’s still routine, just doesn’t happen with nearly the frequency.

Keep in mind that, depending on the jet, you can also save brake wear taxiing on one, in addition to fuel.

N757ST wrote:

I don’t see what the big deal is with single engine taxi. You guys are making it out to be way harder then it is. Does it save fuel? Yes, certainly it does in many circumstances. Every, and I mean every single airline in the USA has a single engine taxi program. There is a little to no risk in single engine taxiing as long as you are patient with break away thrust.

Some comments to address....

What happens if the other motor doesn’t start: well, you have a lot bigger problem on your hands potentially, and are likely doing a gate return.

What happens if they tell you to skip then line? Well, you tell them you aren’t ready.

You don’t single engine taxi at BDL or PBI, you do single engine taxi at LGA and JFK. It’s all situational and can save an airline millions annually on their fuel bill.

At my airline, an airbus operator, single engine out is FAR more common then in. In order to single engine taxi in you need to have the APU running on the a320 series. If you have a sub 5 minute taxi what’s the point in wasting an apu start cycle to single engine in. Just pull into the gate with 2 running and shut #2 down once chalked, #1 after being plugged into a GPU.

It's not as easy as you make it sound. What happens when one engine isn't running? Your Engine Driven Hydraulic Pump isn't powered. Your Engine Driven Generator isn't powered. You aren't getting bleed air from that engine. There are a multitude of system effects of varying complexity, depending on model. It gets more complex for models like the 787 with integrated systems. For example, it may be recommended to do things in a certain order that are different from your normal pre-flight procedure. That increases the possibility of error or a missed step.

You also may be rushing things like the Checklists (because on some FBW models you can't do the Flight Controls Sweep until both engines are running without getting a bunch of system faults).

Especially on an older model without Autostart (e.g. 757, 767, 737), one pilot has to go heads down for a significant time while you are taxiing.

Boeing issued about a 35 page bulletin for each model describing system effects and considerations with single engine taxi. I know a little bit about that bulletin. Obviously, some people don't feel it's completely trivial.

By the way, in regards to several comments made in this thread, Engine Warm-Up and Cool-Down times (usually 3-5 minutes depending on engine type) are not mandatory. They are recommended for engine wear and maintenance purposes. The engine doesn't die if one time you don't adhere to the recommended time.

Single taxi out worked like a treat on the ATR, however, it gets more complicated as the size of the airplanes increases. Did it a couple of times on the A330, but scared myself in the process. To get the thing moving, I needed a handful of thrust and those big engines can make a lot of jet blast, and or ingest some FOD, which will definitely negate any possible savings... As BoeingGuy mentioned, it gets even more complicated on the 787 due to system logic, load shedding etc...

@BoeingGuy - since you seem to be quite well involved with technical considerations of SE taxi. What do you think of starting both engines to break away, start moving, then shutting one engine for duration of taxi and then re-starting it before reaching the runway?

I’ve seen people do it, but wonder if an extra start cycle has any detrimental effects on engine wear? It just doesn’t seem right to switch the engine on and off and on again...

BoeingGuy wrote:

N757ST wrote:

I don’t see what the big deal is with single engine taxi. You guys are making it out to be way harder then it is. Does it save fuel? Yes, certainly it does in many circumstances. Every, and I mean every single airline in the USA has a single engine taxi program. There is a little to no risk in single engine taxiing as long as you are patient with break away thrust.

Some comments to address....

What happens if the other motor doesn’t start: well, you have a lot bigger problem on your hands potentially, and are likely doing a gate return.

What happens if they tell you to skip then line? Well, you tell them you aren’t ready.

You don’t single engine taxi at BDL or PBI, you do single engine taxi at LGA and JFK. It’s all situational and can save an airline millions annually on their fuel bill.

At my airline, an airbus operator, single engine out is FAR more common then in. In order to single engine taxi in you need to have the APU running on the a320 series. If you have a sub 5 minute taxi what’s the point in wasting an apu start cycle to single engine in. Just pull into the gate with 2 running and shut #2 down once chalked, #1 after being plugged into a GPU.

It's not as easy as you make it sound. What happens when one engine isn't running? Your Engine Driven Hydraulic Pump isn't powered. Your Engine Driven Generator isn't powered. You aren't getting bleed air from that engine. There are a multitude of system effects of varying complexity, depending on model. It gets more complex for models like the 787 with integrated systems. For example, it may be recommended to do things in a certain order that are different from your normal pre-flight procedure. That increases the possibility of error or a missed step.

You also may be rushing things like the Checklists (because on some FBW models you can't do the Flight Controls Sweep until both engines are running without getting a bunch of system faults).

Especially on an older model without Autostart (e.g. 757, 767, 737), one pilot has to go heads down for a significant time while you are taxiing.

Boeing issued about a 35 page bulletin for each model describing system effects and considerations with single engine taxi. I know a little bit about that bulletin. Obviously, some people don't feel it's completely trivial.

By the way, in regards to several comments made in this thread, Engine Warm-Up and Cool-Down times (usually 3-5 minutes depending on engine type) are not mandatory. They are recommended for engine wear and maintenance purposes. The engine doesn't die if one time you don't adhere to the recommended time.

I mean, I’m also well aware of the intricacies of single engine taxi man. An engine driven pump out? You still have all three systems running with the PTU or electric pump on. (Our SOP is to power our yellow system with an electric pump selected on) Complexities with starting the motor and checklists? It’s a pretty short list mostly accomplished with flows, and besides, that’s why I get paid like a professional. A generator out? Still got 2 running. I mean, I don’t see the risk here. Engine warmup? Most, including my airline have a minimum warm up time. For the V2500 it’s 5 minutes with a cold motor and 2 minutes with a warm one. As a professional we’re taught to figure out the taxi line and determine when to start engine 2. If you start it too late, suck up the embarrassment and tell tower you aren’t ready.

On a 787 it would be a no brainier really. With the high levels of automated system management you would run the prestart check list, start one engine and then later when you start the 2nd engine you switch on the start switch and the fuel cutoff switch (in any order if you wish to) and the aircraft would autostart the 2nd engine and automatically bring the 2nd engines VFSG's (generators) and EDP (hydraulic pump) on line.

The only difference between running one engine or both is two switches because everything else is already preset prior to starting the first engine. As a plus, you don't have to manage pneumatic loads because for the most part a 787 doesn't have a bleed air system except for engine inlet de-ice and engine active clearance control.

I would imagine that starting and stopping the 2nd engine several times would be frowned upon because it would add unnecessary cycles to the engine.

stratclub wrote:

On a 787 it would be a no brainier really.

During training I was told by Boeing instructors that Boeing didn't recommend it - unlike the 'Bus, which has appropriate SE taxi procedures published in the FCOM.

I stand to be corrected, though. If there's any official Boeing guidance on this, I would love to see it.

I would imagine that starting and stopping the 2nd engine several times would be frowned upon because it would add unnecessary cycles to the engine.

That's what I thought, too...

stratclub wrote:

On a 787 it would be a no brainier really. With the high levels of automated system management you would run the prestart check list, start one engine and then later when you start the 2nd engine you switch on the start switch and the fuel cutoff switch (in any order if you wish to) and the aircraft would autostart the 2nd engine and automatically bring the 2nd engines VFSG's (generators) and EDP (hydraulic pump) on line.

The only difference between running one engine or both is two switches because everything else is already preset prior to starting the first engine. As a plus, you don't have to manage pneumatic loads because for the most part a 787 doesn't have a bleed air system except for engine inlet de-ice and engine active clearance control.

I would imagine that starting and stopping the 2nd engine several times would be frowned upon because it would add unnecessary cycles to the engine.

Actually, it's very far from a no brainer on the 787. While the engines have Autostart as you allude to (just like quite a few other models), it's very complex on the 787 due to the interaction between the flight controls and engines running, and the hydraulic systems on engines running. I don't want to post all the system details here, but there are so many systems related issues with single engine out taxi on the 787 that it's really not recommended.

I think officially Boeing would probably want you to not turn on fuel until you verified rotation of N1 perhaps because you would not have a ground observer if you were taxiing. I can't remember, but I do remember about the auto start function and from what I learned the aircraft would have no problem with you turning on fuel first because the ECU will not turn on fuel until the conditions are right and if you get an unsuccessful start it will do an autostart on the ground IIRC up to 3 times and unlimited autostarts if you have a flameout in flight.

I'm not a pilot but do have a far amount of experience ground running the 787 engines for maintenance and testing. Retired now though.............

thepinkmachine wrote:

What do you think of starting both engines to break away, start moving, then shutting one engine for duration of taxi and then re-starting it before reaching the runway?

I’ve seen people do it, but wonder if an extra start cycle has any detrimental effects on engine wear? It just doesn’t seem right to switch the engine on and off and on again...

Doing this makes no sense whatsoever. If you're stuck in traffic at JFK, you're going to be doing a lot of starting and stopping on the taxiway. Are you going to start the engine every time you get the plane moving, and then shut it down again once you get rolling before you have to stop the plane again?

BoeingGuy wrote:

stratclub wrote:

On a 787 it would be a no brainier really. With the high levels of automated system management you would run the prestart check list, start one engine and then later when you start the 2nd engine you switch on the start switch and the fuel cutoff switch (in any order if you wish to) and the aircraft would autostart the 2nd engine and automatically bring the 2nd engines VFSG's (generators) and EDP (hydraulic pump) on line.

The only difference between running one engine or both is two switches because everything else is already preset prior to starting the first engine. As a plus, you don't have to manage pneumatic loads because for the most part a 787 doesn't have a bleed air system except for engine inlet de-ice and engine active clearance control.

I would imagine that starting and stopping the 2nd engine several times would be frowned upon because it would add unnecessary cycles to the engine.

Actually, it's very far from a no brainer on the 787. While the engines have Autostart as you allude to (just like quite a few other models), it's very complex on the 787 due to the interaction between the flight controls and engines running, and the hydraulic systems on engines running. I don't want to post all the system details here, but there are so many systems related issues with single engine out taxi on the 787 that it's really not recommended.

I can imagine that if you are at MTOW, starting out from a stop would put a pretty good side load on the NG. Single engine taxi? I would tend to agree that it would not be recommended probably because you could set an EICAS message that would require a ground test to clear. I've never taxied a 787, so I just plain old don't what is allowed.

When I post on the interwebs, something I always do is a Google search and if I can find the info on the web I figure it is public domain and I'm not disclosing anything proprietary. Anyway, just a thought.................

stratclub wrote:

BoeingGuy wrote:

stratclub wrote:

On a 787 it would be a no brainier really. With the high levels of automated system management you would run the prestart check list, start one engine and then later when you start the 2nd engine you switch on the start switch and the fuel cutoff switch (in any order if you wish to) and the aircraft would autostart the 2nd engine and automatically bring the 2nd engines VFSG's (generators) and EDP (hydraulic pump) on line.

The only difference between running one engine or both is two switches because everything else is already preset prior to starting the first engine. As a plus, you don't have to manage pneumatic loads because for the most part a 787 doesn't have a bleed air system except for engine inlet de-ice and engine active clearance control.

I would imagine that starting and stopping the 2nd engine several times would be frowned upon because it would add unnecessary cycles to the engine.

Actually, it's very far from a no brainer on the 787. While the engines have Autostart as you allude to (just like quite a few other models), it's very complex on the 787 due to the interaction between the flight controls and engines running, and the hydraulic systems on engines running. I don't want to post all the system details here, but there are so many systems related issues with single engine out taxi on the 787 that it's really not recommended.

I can imagine that if you are at MTOW, starting out from a stop would put a pretty good side load on the NG. Single engine taxi? I would tend to agree that it would not be recommended probably because you could set an EICAS message that would require a ground test to clear. I've never taxied a 787, so I just plain old don't what is allowed.

When I post on the interwebs, something I always do is a Google search and if I can find the info on the web I figure it is public domain and I'm not disclosing anything proprietary. Anyway, just a thought.................

Noted. That’s why I didn’t put out all the system details of the 787 in single engine taxi. But maybe even take a step back from that next time.

N757ST wrote:

I don’t see what the big deal is with single engine taxi. You guys are making it out to be way harder then it is. Does it save fuel? Yes, certainly it does in many circumstances. Every, and I mean every single airline in the USA has a single engine taxi program. There is a little to no risk in single engine taxiing as long as you are patient with break away thrust.

Some comments to address....

What happens if the other motor doesn’t start: well, you have a lot bigger problem on your hands potentially, and are likely doing a gate return.

What happens if they tell you to skip then line? Well, you tell them you aren’t ready.

You don’t single engine taxi at BDL or PBI, you do single engine taxi at LGA and JFK. It’s all situational and can save an airline millions annually on their fuel bill.

At my airline, an airbus operator, single engine out is FAR more common then in. In order to single engine taxi in you need to have the APU running on the a320 series. If you have a sub 5 minute taxi what’s the point in wasting an apu start cycle to single engine in. Just pull into the gate with 2 running and shut #2 down once chalked, #1 after being plugged into a GPU.

Except when you have to keep that engine running for 10 minutes until ramp
plugs in ground power


Then all those savings are gone !

Max Q wrote:

N757ST wrote:

I don’t see what the big deal is with single engine taxi. You guys are making it out to be way harder then it is. Does it save fuel? Yes, certainly it does in many circumstances. Every, and I mean every single airline in the USA has a single engine taxi program. There is a little to no risk in single engine taxiing as long as you are patient with break away thrust.

Some comments to address....

What happens if the other motor doesn’t start: well, you have a lot bigger problem on your hands potentially, and are likely doing a gate return.

What happens if they tell you to skip then line? Well, you tell them you aren’t ready.

You don’t single engine taxi at BDL or PBI, you do single engine taxi at LGA and JFK. It’s all situational and can save an airline millions annually on their fuel bill.

At my airline, an airbus operator, single engine out is FAR more common then in. In order to single engine taxi in you need to have the APU running on the a320 series. If you have a sub 5 minute taxi what’s the point in wasting an apu start cycle to single engine in. Just pull into the gate with 2 running and shut #2 down once chalked, #1 after being plugged into a GPU.

Except when you have to keep that engine running for 10 minutes until ramp
plugs in ground power


Then all those savings are gone !

Can’t you just have the APU running?

Max Q wrote:

N757ST wrote:

I don’t see what the big deal is with single engine taxi. You guys are making it out to be way harder then it is. Does it save fuel? Yes, certainly it does in many circumstances. Every, and I mean every single airline in the USA has a single engine taxi program. There is a little to no risk in single engine taxiing as long as you are patient with break away thrust.

Some comments to address....

What happens if the other motor doesn’t start: well, you have a lot bigger problem on your hands potentially, and are likely doing a gate return.

What happens if they tell you to skip then line? Well, you tell them you aren’t ready.

You don’t single engine taxi at BDL or PBI, you do single engine taxi at LGA and JFK. It’s all situational and can save an airline millions annually on their fuel bill.

At my airline, an airbus operator, single engine out is FAR more common then in. In order to single engine taxi in you need to have the APU running on the a320 series. If you have a sub 5 minute taxi what’s the point in wasting an apu start cycle to single engine in. Just pull into the gate with 2 running and shut #2 down once chalked, #1 after being plugged into a GPU.

Except when you have to keep that engine running for 10 minutes until ramp
plugs in ground power


Then all those savings are gone !

Well, that’s why you have procedures. At my airline we have safe dock systems and the kill switches have been disabled on all our jetbridges system wide. Airplane pulls in, is chaulked and immediately plugged in. If you see a delay such as an occupied gate or such, start the apu in order to shut down engine #2. We have cool down time limits as well as warm up, so by the time you get to the gate generally you are within the cooldown window anyways. (It’s either wait 2 mins for cooldown or blocked in to shut a motor down, whichever is first.)

As with everything, we use basic judgement whether to fire up the APU on taxi in.

BoeingGuy wrote:

Max Q wrote:

N757ST wrote:

I don’t see what the big deal is with single engine taxi. You guys are making it out to be way harder then it is. Does it save fuel? Yes, certainly it does in many circumstances. Every, and I mean every single airline in the USA has a single engine taxi program. There is a little to no risk in single engine taxiing as long as you are patient with break away thrust.

Some comments to address....

What happens if the other motor doesn’t start: well, you have a lot bigger problem on your hands potentially, and are likely doing a gate return.

What happens if they tell you to skip then line? Well, you tell them you aren’t ready.

You don’t single engine taxi at BDL or PBI, you do single engine taxi at LGA and JFK. It’s all situational and can save an airline millions annually on their fuel bill.

At my airline, an airbus operator, single engine out is FAR more common then in. In order to single engine taxi in you need to have the APU running on the a320 series. If you have a sub 5 minute taxi what’s the point in wasting an apu start cycle to single engine in. Just pull into the gate with 2 running and shut #2 down once chalked, #1 after being plugged into a GPU.

Except when you have to keep that engine running for 10 minutes until ramp
plugs in ground power


Then all those savings are gone !

Can’t you just have the APU running?

SMH yes you have already said what I have been thinking all along. The desired thing the bean counters want is single engine taxi to the gate, no APU and fast and speedy ground crew right there at the ready with the GPU to plug it in so they can shut the remaining engine down all the interest of saving fuel..But you and I know that isn't how it works in the real world. In the real world it is like you said the remaining running engine will run for up to maybe 10 mins at the gate for them to hook up external power even running an APU would be less expensive than that so what did you save?

Most airlines have single engine taxi SOPs devised and practised. As pilots we are expected to assess then decide if we are going to use them. As noted above, there are specific reasons when one would not.

stratosphere wrote:

In the real world it is like you said the remaining running engine will run for up to maybe 10 mins at the gate for them to hook up external power even running an APU would be less expensive than that so what did you save?

Technically, you still saved the fuel gained by the single engine taxi.

Having to wait for a gate with engine(s) running is a different issue, and as airlines look to save all possible, this is one area being addressed. We are encouraged to send a report advising the flight/date/gate and time waited. It is a page in the MCDU with blanks easily filled. I do it often as it wont get fixed otherwise.

thepinkmachine wrote:

Single taxi out worked like a treat on the ATR, however, it gets more complicated as the size of the airplanes increases. Did it a couple of times on the A330, but scared myself in the process. To get the thing moving, I needed a handful of thrust and those big engines can make a lot of jet blast, and or ingest some FOD, which will definitely negate any possible savings... As BoeingGuy mentioned, it gets even more complicated on the 787 due to system logic, load shedding etc...

@BoeingGuy - since you seem to be quite well involved with technical considerations of SE taxi. What do you think of starting both engines to break away, start moving, then shutting one engine for duration of taxi and then re-starting it before reaching the runway?

I’ve seen people do it, but wonder if an extra start cycle has any detrimental effects on engine wear? It just doesn’t seem right to switch the engine on and off and on again...

In answer to your question, yes I’ve heard it recommended that you start both engines at gate and get away using normal breakaway power. Then if you get in a long conga line, you can shut one down. IIRC, this is mandatory on the 787 due to some systems issues that I’ve alluded to earlier.

FYI... 'off-to-the-side' contribution to single engine OPs in a twin-Jet...

SOP for A-37Bs during combat patrols/over-watch [Vietnam war] was to climb to between 18K to 22K altitude... then shut down one of the J-85 engines to conserve fuel while loiter-orbiting for a 'strike call'. Usually added up-to1-hr to loiter-time [relative to 2-engines running inefficiently at low power]... so this kept these little jets with ordnance on-station for a far-longer time relative to any of the 'fast movers'. As I recall the pilots alternated engine shut-downs to balance the stresses on the engines. This long-loiter/QR capability was really appreciated by troops in-contact.

Immediately on a 'frag-order strike call' the pilot would initiate course-change, rapid descent and engine re-start procedures. About 2-to-3 minutes later, approaching the target area, with both engines up/running, the jet was 'hot' and ready to fight.

NOTE. During loiter the pilots weren't just taking a nap... all reported intently watching and listening-to the ground combat/AAA/artillery/etc activity... plus HELO-ops, FAC-ops, etc... while itching to inflict accurate/critical damage on unsuspecting VC/NVA forces [and often heavy vehicles] 'where/as-needed'. IF their loiter area was running slow, they were sometime redirected to ‘work targets’ of higher priority miles-away.

NOTE. The A-37s [A and B] models were so small and quiet that they often caught the enemy unprepared to react to the 'sneaky attack runs'. Pilots loved to have a 'shake-N-bake' combos under wings so they could inflict a wide range of damage: napalm, bombs and rockets... and 762 minigun with ~1200-shots... plus 2 extra drop-tanks.

Interesting NOTE. Even though the practice of shutting-down an engine was SOP during war, in later [non-war] years of service [~1980s], younger pilots were more reluctant to shut-down an engine 'just because the procedure wasn't standard in any other jet in the USAF inventory'... and the 'veteran pilots' who understood the procedures well, had mostly filtered-out of the TAC units.

P-3s would also shut down engines in flight to extend playtime.

I wonder if they'd be able to convince the P-8 pilots to shut down an engine to extend playtime today.

WKTaylor wrote:

FYI... 'off-to-the-side' contribution to single engine OPs in a twin-Jet...

......
Interesting NOTE. Even though the practice of shutting-down an engine was SOP during war, in later [non-war] years of service [~1980s], younger pilots were more reluctant to shut-down an engine 'just because the procedure wasn't standard in any other jet in the USAF inventory'... and the 'veteran pilots' who understood the procedures well, had mostly filtered-out of the TAC units.

Not normal for line pilots, but as an FCF (Functional Check Flight) pilot in T-38s it was part of the profile to shut one down and see if it would restart normally. Had several J-85s (the same engine you had in A-37s) that wouldn't restart and RTB'd single engine. As I recall a common phrase MX would use when restarts failed was "wet igniter plug'. But I'm sure there were other reasons.

WKTaylor wrote:

FYI... 'off-to-the-side' contribution to single engine OPs in a twin-Jet...

SOP for A-37Bs during combat patrols/over-watch [Vietnam war] was to climb to between 18K to 22K altitude... then shut down one of the J-85 engines to conserve fuel while loiter-orbiting for a 'strike call'. Usually added up-to1-hr to loiter-time [relative to 2-engines running inefficiently at low power]... so this kept these little jets with ordnance on-station for a far-longer time relative to any of the 'fast movers'. As I recall the pilots alternated engine shut-downs to balance the stresses on the engines. This long-loiter/QR capability was really appreciated by troops in-contact.

Immediately on a 'frag-order strike call' the pilot would initiate course-change, rapid descent and engine re-start procedures. About 2-to-3 minutes later, approaching the target area, with both engines up/running, the jet was 'hot' and ready to fight.

NOTE. During loiter the pilots weren't just taking a nap... all reported intently watching and listening-to the ground combat/AAA/artillery/etc activity... plus HELO-ops, FAC-ops, etc... while itching to inflict accurate/critical damage on unsuspecting VC/NVA forces [and often heavy vehicles] 'where/as-needed'. IF their loiter area was running slow, they were sometime redirected to ‘work targets’ of higher priority miles-away.

NOTE. The A-37s [A and B] models were so small and quiet that they often caught the enemy unprepared to react to the 'sneaky attack runs'. Pilots loved to have a 'shake-N-bake' combos under wings so they could inflict a wide range of damage: napalm, bombs and rockets... and 762 minigun with ~1200-shots... plus 2 extra drop-tanks.

Interesting NOTE. Even though the practice of shutting-down an engine was SOP during war, in later [non-war] years of service [~1980s], younger pilots were more reluctant to shut-down an engine 'just because the procedure wasn't standard in any other jet in the USAF inventory'... and the 'veteran pilots' who understood the procedures well, had mostly filtered-out of the TAC units.

Fascinating,



I’ve also read of NASA Astronauts shutting down one engine in their T38’s to extend range on their cross country flights



Don’t know if they even fly these anymore since the end of the Shuttle program

FlyHossD wrote:

. Seems like single taxi out was common in the regional turboprops, too - I distinctly remember a woman who was concerned about the stationary prop one time.

I've noted that too. I've only taken flights in Dash8 and Q400 turboprops so I don't know if there is a difference with the ATR. 2nd engine start is usually out on the taxiway and shutdown is fast - engine #2 is feathered right after removal of reverse thrust and is shut down a few minutes later.

I tend to see that even after startup on the 2nd engine, the engine is left in feather until lining up for take-off. It makes me wonder about the fuel consumption difference between feathered and ground idle.

Starlionblue wrote:

Both engines at ground idle might well be too much power for taxi, so you have to keep braking.

I didn't think a turboprop made any thrust at disk.

Starlionblue wrote:

MatthewDB wrote:

Starlionblue wrote:

Both engines at ground idle might well be too much power for taxi, so you have to keep braking.

I didn't think a turboprop made any thrust at disk.

That's my point. By only having one prop at ground idle and one disced you get less total thrust than with two at ground idle. So the reason to feather one prop might be mainly to avoid having excess thrust for taxi, and not for fuel savings.

Just speculation. I've never flown a turboprop.

Can't speak for the Q400s, never experienced that myself when flying as a passenger on them.
As for the ATR, the actual propeller position is automatically controlled, and changes constantly. At idle power-lever setting on the ground, it will typically position in something like disc-position with little or no thrust, and once you add some power it will pitch slightly. You can see it on a wet apron, when parked with engines running it doesn't really blow any water aft.
BTW, ATR discourages single-engine taxi-out these days, but it is still common during taxi-in.

stratclub wrote:

greendot wrote:

BoeingGuy wrote:

Of course that could happen. There are other risks with single engine taxi out also. What if you have a tailpipe fire when you start the second engine? You don't have your ground crew nearby to assist (tailpipe fires are not detected by the engine fire detection system).

What if ATC clears you to jump ahead in line and takeoff immediately but your second engine isn't started?

One airline blew a baggage cart into an employee because breakaway power from the gate with only one engine was so high. Another airline had a very near miss on a taxi way because one pilot had his head down starting the second engine.

Some airlines are choosing to live with the risks and do it because they believe it saves fuel.

For these various reasons, Boeing used to provide guidance to the customers prohibiting single engine taxi out. Taxi in was okay in certain cases - having adequate warm down time, etc.

Some airlines like DL said too bad, they are going to do it anyway. Other airlines wanted to do it and asked Boeing to soften that guidance so their own regulatory agencies would permit them to do it. Boeing then figured that the customers are big boys and if they chose to do it, there is no reason to prohibit it. Now technical guidance is provided to the customers of the airplane system effects of doing single engine taxi. The customers can decide if it fits in their operational environment and adopt the safest possible procedures to do so.

• Tailpipe fires are not a big deal... they extinguish on their own. However, there are OTHER uncontained fire types and having no immediate fire fighting could be a big problem. This is a risk airlines are taking on your behalf. You are correct in that there is the assumption that fire detection systems work and that fire suppression systems likewise put the fire out. Lastly, there is the presumption that airport firefighters can get there quick enough and that people can evacuate these ultra-high density loads in the event of a fire that won't go out. Your concern is very legitimate: https://en.wikipedia.org/wiki/British_A ... Flight_28M
  Thank you federal government (FAA) for proving once again that safety is not the most important thing.
• If ATC clears you jump into an intersection to skip ahead, you just have to communicate your limitation. Most all new designs require an engine warmup time that can be upwards of 5 minutes at Idle thrust. Pilots have to use their experience to decide when to start the second engine for scenarios like this.
• Taxiing incidents are certainly a big risk. This is a glaring safety issue that the FAA will not address because the airlines don't want to.
• Airlines live with TONS of risks because it doesn't cost them anything. The regulatory requirements are not very high. Plus, in order to win in court, you have to prove things while fighting high paid corporate lawyers. The burden of proof standard is not the problem. The problem is that it's up to you to gather the evidence to make your case. Good luck getting company proprietary data. Look up Aerotoxic Syndrome ( https://en.wikipedia.org/wiki/Aerotoxic_syndrome) and you'll see something that affects the entire industry yet lawsuits have been unsuccessful. It's an uphill battle like proving that smoking is unhealthy. There have been some industry successes (elsewhere) such as a gardener winning against Monsanto because he got terminal cancer. https://www.cbc.ca/news/health/monsanto-payment-cancer-roundup-1.4781751

Taxiing single engine does save fuel. We do that sometimes when our minimum takeoff fuel is very close to our fuel loadout particularly at airports where taxi times can exceed 1 hour.

The FAA has absolutely no rules preventing the practice. I don't really think they should but there certainly are some risks involved. I'm fairly neutral on whether this is good or bad overall but there certainly are some issues with it.

A lot of assumptions not based in fact. How exactly is a delayed engine start higher risk than an engine start at push back? It isn't. The fire suppression system does absolutely nothing for core fires while a fire in the fire suppression zones could happen even in flight. So should we have a firetruck fly with the aircraft? I guess that would satisfy your assumption of required safety procedures.

It depends on what you trying to achieve. The general premise of the question is to have the safest possible conditions. One engine taxis are not because you don't have auxiliary fire protection until the fire fighters arrive. Therefore, it isn't the safest possible condition. So let's go back to the idea of what you're trying to achieve. In the USAF, I once flew a black colored big airplane that cost a lot of money. You better believe we always had a massive ground crew presence at all times, particularly during engine start. We couldn't afford to lose something so expensive to engine fires during start. Now, in my civilian career, we routinely start engines after we push back. I'm just stating the fact that one mode of operation is safer than the other because there are more layers of protection during that critical starting phase.