Suppose the captain of a modern transport aircraft of, say, B737/A320 class, while rolling for take-off, some ten knots before V1, sees the fuel flow rate of one engine to increase dramatically. Logically, the most likely cause must be a leak downstream of the fuel flow metering device that is a fuel leak in the engine's nacelle. It seems to me that engine fire is the most likely outcome. Would it be prudent to reject the take-off in such situation before the fire horn sounds?

If I were in that situation of course I would reject, assuming I haven't hit V1 yet. Safety over all.

On the A320 I would not reject in this scenario. A high speed RTO at more than 100kts can be hazardous due to the potential for an overrun and there are just very few defined failures that will lead to an RTO in this situation. Also, the human brain is not capable of noticing and processing a single drifting parameter within the short time frame between V1-10kts and V1. By the time you have realized what is going on the speed would already be above V1. Also I would guess that the most likely cause for a sudden increase in fuel flow (with all other parameters stable) would be an indication error.

As an aside, would you really be looking at the fuel flow 10 knots before V1?

Flow2706 wrote:

On the A320 I would not reject in this scenario. A high speed RTO at more than 100kts can be hazardous due to the potential for an overrun and there are just very few defined failures that will lead to an RTO in this situation. Also, the human brain is not capable of noticing and processing a single drifting parameter within the short time frame between V1-10kts and V1. By the time you have realized what is going on the speed would already be above V1. Also I would guess that the most likely cause for a sudden increase in fuel flow (with all other parameters stable) would be an indication error.

THIS, plus airborne with the air flow, it’s less likely to ignite, if it was going to light. Then, airborne try to confirm what is happening. If the fuel stream is showing on the cowl or streaming near the cowl, declare the emergency, if the QRH calls for it, type specific but likely shut the engine down, of course. Brief the cabin crew for possible evacuation and which side you want them to open, if there is a fire on the ground. Brief ATC, roll the equipment to be ready on the affected side.

Starlionblue wrote:

As an aside, would you really be looking at the fuel flow 10 knots before V1?

My thoughts exactly

The fuel flow at takeoff is already “insanely” high compared to normal cruise fuel flow.

But it’s unlikely you’re going to notice it at v1-10.

You do notice when the engine is not producing thrust as the plane veers and you have to make a correction to maintain centerline.

There’s very few things that I’d reject right before v1. It’s better to take it into the air and deal with it up in the air where there’s more time to deal with it and set up for the return.

Classically, there are only two things: complete loss of thrust in at least one engine and actual fire. Do You really know any other?

I’ve been given uncommanded TR deployed, loud bang and high vibration, compressor stall and power rollback.

IanfromRussia wrote:

Classically, there are only two things: complete loss of thrust in at least one engine and actual fire. Do You really know any other?

We practiced compressor stall at takeoff and on one sim we got a tire burst around V1. This was very tricky as we rarely ever practice this and initially it's very easy to mistake it for an engine failure, so obviously you'll try to raise the gear after liftoff which you shouldn't do with a damaged tire. Other interesting engine malfunctions (on the Airbus, other types may have different systems) are FADEC Faults (will result in the loss of all engine related indications and probably also lead to an engine shutdown) and Thrust lever faults/Thrust lever disagree. Recently I have seen fuel leaks a lot in the simulator scenarios - but in the sim scenarios I had the leak was always happening in flight, not during takeoff.

It this issue trigger a Master Warning, Master Master Caution, a long of thrust/Engine failure, loss of directional control, or renders the aircraft unsafe or unable to fly at 10 knots V1. If the answer is No, then I am not rejecting. I would take into the air as there would be a better chance and safer to deal with the situation in the air.

Anytime you are above 80kts on the T/O roll, you are looking at a high speed reject and a lot can go wrong very quickly. You have to be certain, about the above conditions.

Below 80 it’s, if anythibg not right. No problem, Reject.

bigb wrote:

It this issue trigger a Master Warning, Master Master Caution, a long of thrust/Engine failure, loss of directional control, or renders the aircraft unsafe or unable to fly at 10 knots V1. If the answer is No, then I am not rejecting. I would take into the air as there would be a better chance and safer to deal with the situation in the air.

Anytime you are above 80kts on the T/O roll, you are looking at a high speed reject and a lot can go wrong very quickly. You have to be certain, about the above conditions.

Below 80 it’s, if anythibg not right. No problem, Reject.

I believe most modern airliners have a diminishing number of events that will trigger a master caution / warning the faster you go. At 40kt something fairly benign may trigger it, but by the time you get to 80kt and above the list of warnings that are 'inhibited' until you are airborne gets to the point of pretty much being engine failure only (there may be a few others as well)

Then once passing a certain altitude (400ft ?) the warnings will go off.

Woodreau wrote:

The fuel flow at takeoff is already “insanely” high compared to normal cruise fuel flow.

But it’s unlikely you’re going to notice it at v1-10.

Shown here, the four long vertical white bars are fuel flow.

http://www.youtube.com/watch?v=3J7K-DxlgOs&t=5s

77west wrote:

bigb wrote:

It this issue trigger a Master Warning, Master Master Caution, a long of thrust/Engine failure, loss of directional control, or renders the aircraft unsafe or unable to fly at 10 knots V1. If the answer is No, then I am not rejecting. I would take into the air as there would be a better chance and safer to deal with the situation in the air.

Anytime you are above 80kts on the T/O roll, you are looking at a high speed reject and a lot can go wrong very quickly. You have to be certain, about the above conditions.

Below 80 it’s, if anythibg not right. No problem, Reject.

I believe most modern airliners have a diminishing number of events that will trigger a master caution / warning the faster you go. At 40kt something fairly benign may trigger it, but by the time you get to 80kt and above the list of warnings that are 'inhibited' until you are airborne gets to the point of pretty much being engine failure only (there may be a few others as well)

Then once passing a certain altitude (400ft ?) the warnings will go off.

Exactly. If you get an engine failure after V1 on the A330, for example, you'll get the ECAM messages, but the master warning won't start ringing until 400ft AAL.

As a pilot with 42 years in military and commercial aviation, the short answer is absolutely NO. I have only flown the Lockheed C130 and Boeing 737, 747 and 787 so cannot comment on Airbus.

To fully answer your question and to state the reasons for my answer of No, there are lots to consider, so please bear with me.

1. On a modern Boeing aircraft, Fuel Flow indication may or may not visible during the take off (and inflight) portion of flight, and this all depends on the CDS (Common Display System) software option that an Airline pays to configure its fleet. In my previous Airlines, flying the 737, and 787, this was a mixed bag. However, for the most part the Upper DU (Display Unit) on a 737 is blanked after engine start and the only visible ‘engine displays’ are N1 and EGT. As mentioned some Airlines may pay for the CDS to have a compact display that will show the remaining ‘engine displays’ in a mini format after the Upper DU is blanked. The design of the 737 is that if an exceedance occurs for a blanked display it will pop up on the Upper DU (ie. all engine indications are now visible). However, this does not happen for fuel flow indications. So a high fuel flow would not activate the pop up feature.
2. A real high speed RTO (classed as greater than 80kts) is an extremely violent, risky and unpleasant experience. The Boeing philosophy is that above 80kts and prior to V1, you only Reject for a Fire or Fire Warning, Engine Failure, Predictive Windshear Warning or the Airplane is unsafe or unable to Fly. A high fuel flow (even if you were to spot this) does not fit any of these criteria. In my career so far, I have carried out 30 actual RTO’s (1 on a C130, 1 on a 747, 18 on 737’s and 10 on 787’s). Of these 30 RTO’s, only 5 were for actual RTO’s for an aircraft malfunction and all of these were thankfully below 80kts. The other 25 were carried out in Seattle at the Boeing factory when I was an acceptance pilot for my Airline and I accepted and delivered 15 737’s and 10 787’s. During the Acceptance flights at Boeing one of the last test events is an RTO carried out at 90kts. Even at this relatively low airspeed the RTO is violent and places extreme stress on the airplane and is extremely efficient at stopping the airplane. The physical forces of an RTO just cannot be duplicated in a simulator and for this reason there may be a lot of pilots out there that think an RTO is a walk in the park. I can assure it is not. All of my actual RTO (ie. not the ones at the Boeing factory) have been low speed RTO’s where the Autobrake is not automatically activated and the stopping distance is not a problem, so this manoeuvre can be carried out gently with minimal braking effort.
3. As mentioned a high speed RTO is a risky event. Yes we train for this in the simulator every 6 months and rightly so for many reasons. We brief it prior to first flight of the day. Most Airlines use Balanced V1 for take off performance. This means that the V1 and Vr speeds are increased to a much higher speed (possibly by up to 20-25kts higher) to utilise most of the available runway. This allows for a reduced N1 and EGT and therefore reduced maintenance costs, as well as improve departure climb gradients. The negative impact of this is that the available runway from V1 to the runway end is greatly reduced. If an RTO is carried out it must be done accurately and without delay. In the sim we are prepared for RTO’s and in a way is a canned environment (we know its coming and prepared). On the line, although we brief we still do not expect an RTO (they are rare events) and the startle effect of an RTO listed malfunction may mean lost seconds in identifying and accepting you have a problem and must act. This is why the RTO philosophy reduces the number of mandatory events for an RTO above 80kts to just a few. As some on here have already mentioned newer airplanes inhibit warnings/cautions to crews so that they do not reject for minor issues. It’s better to take the airplane into the air and sort it out there than reject and lose a hull and/or risk life.
4. Your scenario of a high fuel flow that in your words might mean a fuel leak and a ‘potential’ fire, raises a serious question. What if your fuel flow indication was a false indication? It does happen and I’ve seen it before. Rejecting for a perceived fault that does not fit the Boeing RTO philosophy would place a pilot in a very difficult situation explaining it to his/her Chief Pilot and the National Aviation Authority. Also at 10kts below V1 there would be so much braking energy required to stop the plane that you will most likely deflate all your main wheels via the fuse plugs. This will mean blocking the runway for a long period of time, having to bus your frightened pax to the terminal, having to have the airplane jacked to replace the tyres to clear the runway, etc, etc.
5. Fluid is a lazy element and it will always take the path of least resistance. If there truly was a fuel leak that resulted in your scenario of a large increase in fuel flow indication between the fuel flow transmitter and the fuel nozzle, I would first expect to see a yaw toward that engine with an loss of thrust on that engine, as the fuel will port to the leak (least resistance) and not the resistance required to pass via the fuel nozzles. If the leak in your scenario was a small leak emitting a fine spray, I doubt this would increase fuel flow that much, and probably wouldn't even be noticeable.
6. If this scenario was to take place the QRH fuel leak checklist can be quite a complex and is a time consuming process. Unless fuel spray is visible from the engine, the shutting down of an engine is the final step after exhausting all other checks, which could take as long as 30 minutes of more.
7. My question to you now. What if you have the opposite of your scenario - discounting the fact of whether you see or do not see the fuel flow indication at high speed on the runway. At 10kts before V1, your engines are set to the required take off thrust, there is no yaw, but the fuel flow indication dropped toward zero or even decreased to zero, would you reject the take off? I know what I would do - and wouldn't destroy my career with an unnecessary RTO.

DOG

I'll add to Dogbreath's excellent post that the Airbus philosophy is really no different. The FCTM emphasizes strongly that high speed RTOs are not to be taken lightly.

Physics is physics, regardless of type.

From the A330 FCTM:

DECISION MAKING
A rejected takeoff is a potentially hazardous manoeuvre and the time for decision making is limited. It is not possible to list all the factors that could lead to the decision to reject the takeoff. However, in order to help the Captain to make a decision, the ECAM inhibits the warnings that are not essential from 80 kt to 1 500 ft (or 2 min after lift-off, whichever occurs first). Therefore, any warning received during this period must be considered as significant.

SPEED CONSIDERATIONS
To assist in the decision making process, the takeoff is divided into low and high speeds regimes, with 100 kt being chosen as the dividing line. The speed of 100 kt is not critical but was chosen in order to help the Captain make the decision and to avoid unnecessary stops from high speed.

***

 Above 100 kt, and below V1:
Rejecting the takeoff at these speeds is a more serious matter, particularly on slippery runways. It could lead to a hazardous situation, if the speed is approaching V1. At these speeds, the Captain should be "go-minded" and very few situations should lead to the decision to reject the takeoff.

Dogbreath wrote:

On the line, although we brief we still do not expect an RTO (they are rare events) and the startle effect of an RTO listed malfunction may mean lost seconds in identifying and accepting you have a problem and must act....

As some on here have already mentioned newer airplanes inhibit warnings/cautions to crews so that they do not reject for minor issues.

DOG

That confuses me a bit. If all warnings not pertaining to the RTO are inhibited in modern aircraft, wouldn't that mean that the horn must trigger the captain to slam the throttles back automatically? Or there is still a need for some assessment?
What does nean "newer" in this context? Is, e. g., a 737NG manufactured in early 2000s a "newer" or an "older" plane?

P. S. If something I say seems silly to You, consider that I'm not a pilot myself but an aeronautical engineer.

77west wrote:

bigb wrote:

It this issue trigger a Master Warning, Master Master Caution, a long of thrust/Engine failure, loss of directional control, or renders the aircraft unsafe or unable to fly at 10 knots V1. If the answer is No, then I am not rejecting. I would take into the air as there would be a better chance and safer to deal with the situation in the air.

Anytime you are above 80kts on the T/O roll, you are looking at a high speed reject and a lot can go wrong very quickly. You have to be certain, about the above conditions.

Below 80 it’s, if anythibg not right. No problem, Reject.

I believe most modern airliners have a diminishing number of events that will trigger a master caution / warning the faster you go. At 40kt something fairly benign may trigger it, but by the time you get to 80kt and above the list of warnings that are 'inhibited' until you are airborne gets to the point of pretty much being engine failure only (there may be a few others as well)

Then once passing a certain altitude (400ft ?) the warnings will go off.

Yup, that is correct. That’s due to how critical the decision of performing a high speed reject really is.

Dogbreath wrote:

A real high speed RTO (classed as greater than 80kts) is an extremely violent, risky and unpleasant experience.

DOG

Is it a hard job for a pilot or is it a bit like ejection from a fast jet - You initiate it and pray that it goes the right way?

IanfromRussia wrote:

Suppose the captain of a modern transport aircraft of, say, B737/A320 class, while rolling for take-off, some ten knots before V1, sees the fuel flow rate of one engine to increase dramatically. Logically, the most likely cause must be a leak downstream of the fuel flow metering device that is a fuel leak in the engine's nacelle. It seems to me that engine fire is the most likely outcome. Would it be prudent to reject the take-off in such situation before the fire horn sounds?

The scenario you are describing both engines would still be delivering takeoff thrust, and even if the engine fire indications did start until just after V1, the thrust from both engines would still be takeoff thrust.

It is only during the fire drill when the throttle/thrust lever is brought back to idle and the engine shut down. Only at that stage would there be a reduction in takeoff performance.

This thread reminded me of this youtube video of an A350 that auto-rejected due to a glitch in the runway overrun protection I believe

https://www.youtube.com/watch?v=MKtPlj932YY

It appears they would have been doing around 80kt at the time and shows from the cabin how much of a jolt it gives as well as the impressive performance of the brakes. But I would not be surprised if they deflated a tire or two or at least had to wait a while for the brakes to cool down. Reinforcing that you really don't want to reject unless it is for a very serious reason, which in the Boeing manuals at least uses words to the tune of "...continue the takeoff unless the aircraft is unsafe or unable to fly..."

A fuel leak would not meet either of these criteria. If the left wing fell off, thats a different story.

It’s programmed at 15 ft/second squared on a Global 7500, so basically 0.5 G.

IanfromRussia wrote:

Dogbreath wrote:

On the line, although we brief we still do not expect an RTO (they are rare events) and the startle effect of an RTO listed malfunction may mean lost seconds in identifying and accepting you have a problem and must act....

As some on here have already mentioned newer airplanes inhibit warnings/cautions to crews so that they do not reject for minor issues.

DOG

That confuses me a bit. If all warnings not pertaining to the RTO are inhibited in modern aircraft, wouldn't that mean that the horn must trigger the captain to slam the throttles back automatically? Or there is still a need for some assessment?
What does nean "newer" in this context? Is, e. g., a 737NG manufactured in early 2000s a "newer" or an "older" plane?

P. S. If something I say seems silly to You, consider that I'm not a pilot myself but an aeronautical engineer.

If you get a master warning after 80 knots in a modern airliner, it is presumably something very important. However, decision making remains with the captain. No decision should be taken blindly. For example, if you get an engine fire warning, it is good practice not to just trust ECAM, but also to have a look at the overhead to check if the fire pushbutton is actually blinking before doing anything drastic like shutting the engine down. (The overhead has "direct", unfiltered data.)

If it is a few seconds before V1, perhaps technically the takeoff should be rejected, but it might be less risky to just keep going. The situation is very dynamic.

"There is no problem so bad that you can't make it worse."
- Chris Hadfield

I don't know for the 737, but takeoff inhibit is a thing on the A320 series, which entered service in the 80s.

IanfromRussia wrote:

Dogbreath wrote:

A real high speed RTO (classed as greater than 80kts) is an extremely violent, risky and unpleasant experience.

DOG

Is it a hard job for a pilot or is it a bit like ejection from a fast jet - You initiate it and pray that it goes the right way?

I hope no captain is just praying it goes the right way.

A high-speed RTO is not difficult in terms of actions per se. Thrust back and full reverse while keeping it on the runway. Max autobrake will automatically engage. However, we're talking dozens or hundreds of tonnes moving at high speed on relatively small patches of rubber. That's a lot of energy to manage. Even a small asymmetry can have you veering rapidly towards the edge of the runway. It requires attentive and skillful handling, especially in slippery conditions.

In the case of an engine failure what does come first: tendency to veer off the centerline, the horn or the callout of the PM?
...
Is there a thing other than engine failure that can cause the aircraft to veer sideways and the horn to sound?
And should a captain hearing the horn while struggling to keep the aircraft going straight (assuming he is the PF) wait for the callout of the FO?

You’ll feel the aircraft veer off before any other indication.

The priority is to maintain centerline and after V1 get airborne.

It’s not a Herculean struggle, just step on the rudder pedal. But it is easy to overcontrol if you stomp on the pedal.

Once tracking down the centerline, rotate and takeoff. On an Airbus it’s “easy,” just pull the stick straight back (without any side inputs) and place the bottom of the black square on top of the 10 degree pitch line and let go of the stick. Keep the beta target centered and trim out the rudder forces.

You dont wait for the Monitoring pilot call out.

Like this. https://youtu.be/hLcTgXTTtBY

Woodreau wrote:

The priority is to maintain centerline and after V1 get airborne.

I meant If a captain feels an increasing tendency to veer off and than hears horn after 80/100 kts (Boeing have 80) but before V1, should he reject, or some further confirmation of engine failure is required?
I believe horn wouldn't sound for a blown tire, for example.

Woodreau wrote:

Like this. https://youtu.be/hLcTgXTTtBY

What a gem. Love this, thanks for a laugh this morning.

IanfromRussia wrote:

In the case of an engine failure what does come first: tendency to veer off the centerline, the horn or the callout of the PM?
...
Is there a thing other than engine failure that can cause the aircraft to veer sideways and the horn to sound?
And should a captain hearing the horn while struggling to keep the aircraft going straight (assuming he is the PF) wait for the callout of the FO?

You'd see the aircraft going off centerline and subconsciously correct. Whether the master warning sounds at the same time or later depends on the nature of the failure. In case the aircraft is going off the desired path, in this circumstance or any other, you certainly don't wait for a warning. As mentioned, you'd be correcting before it even entered your conscious thoughts.

Unless the PF does not react at all, the PM should not be in a hurry to call something. This is not the time to distract the PF. You might call "engine failure" but it is good practice not to call which engine, because if you call the wrong one, or if the PF misunderstands you, he might put in the wrong control input.

It should be noted that if the engine just rolls back the yaw moment isn't very strong. On the other hand, if the low pressure spool seizes and stops, you'll get a strong yaw moment.

Just to be clear, the above applies to engine failure. If you have an engine fire, on the other hand, as Zeke says the engine is still producing thrust, so you probably would not get a significant yaw moment.

Other things that can cause an aircraft to veer sideways are a locked brake, an uncommanded asymmetrical surface deflection, a strong gusting crosswind, a tyre burst, or a reverser deploying.

IanfromRussia wrote:

Woodreau wrote:

The priority is to maintain centerline and after V1 get airborne.

I meant If a captain feels an increasing tendency to veer off and than hears horn after 80/100 kts (Boeing have 80) but before V1, should he reject, or some further confirmation of engine failure is required?
I believe horn wouldn't sound for a blown tire, for example.

In this case, you have two independent indications of engine failure. One is the yaw moment and another is the master warning and associated message.

As I see it, this would be enough reason to reject unless you're very close to V1. That being said, every situation is different and the decision rests with that particular Captain at that particular time.

The master warning would indeed not sound for a burst tyre. The manuals mention that it is typically better to get airborne even if there is an indication of a tyre burst. Continuing the takeoff and coming back to land with the entire runway is less hazardous than trying to stop in the remaining distance.

Starlionblue wrote:

In this case, you have two independent indications of engine failure. One is the yaw moment and another is the master warning and associated message.

I meant that the PF preoccupied with keeping the aircraft going straight would probably have difficulties with checking for an engine failure message himself, and therefore there would be two possible courses of action: 1) to take yawing tendency + horn as a clear sign of engine failure (as no other event is likely to trigger both yawing tendency and master warning) or 2) to wait for the PM calling out the message.
Am I right in understanding Your answer as favouring the first course of action?

IanfromRussia wrote:

Starlionblue wrote:

In this case, you have two independent indications of engine failure. One is the yaw moment and another is the master warning and associated message.

I meant that the PF preoccupied with keeping the aircraft going straight would probably have difficulties with checking for an engine failure message himself, and therefore there would be two possible courses of action: 1) to take yawing tendency + horn as a clear sign of engine failure (as no other event is likely to trigger both yawing tendency and master warning) or 2) to wait for the PM calling out the message.
Am I right in understanding Your answer as favouring the first course of action?

You would not be waiting for the PM to say something.

But let's take a step back for a moment. On a normal takeoff, you stay on centerline and rotate when the PM calls rotate. On a takeoff with an engine failure, you stay on centerline and rotate when the PM calls rotate.

Notice how there is no fundamental difference besides more input being required to stay on centreline. (The rotation would be slightly different, with a lower pitch angle. But that's a detail in context.)

The point is that you're not really "preoccupied" with anything beyond what preoccupied you on a normal takeoff, that is keeping it on centreline, rotating at the appropriate speed, and rotating at the appropriate rate to the appropriate angle.

The manual says that above 100 knots the captain should be "go-minded". This simple statement hides quite a bit of complexity and experience, of course, but it still indicates that you shouldn't overthink it. Captains that have taken overthought it have not infrequently ended up in the grass after trying to reject when they should have continued.

Starlionblue wrote:

But let's take a step back for a moment. On a normal takeoff, you stay on centerline and rotate when the PM calls rotate. On a takeoff with an engine failure, you stay on centerline and rotate when the PM calls rotate.

Notice how there is no fundamental difference besides more input being required to stay on centreline.

The manual says that above 100 knots the captain should be "go-minded".

STOP. I was taught, even as an aeronautical engineer, that one has to abort if the engine fails before V1 and to take off if it happens after V1. The same basically tells Boeing in their manuals (and I suspect that Airbus too). I understand that there may be a grey zone near V1 where You still can take off with somewhat reduced clearance over the runway threshold, and that the actual runway length vs the balanced one may alter the situation. But I'm talking about situation where the captain has to abort if the engine just has failed but should (or even must) go if it hasn't, so the critical task is to recognize the event. And so my question is: should (generally speaking) the captain abort if he has just two cues: pronounced yawing tendency and the sound of master warning (provided that the speed is such that a failed engine means "stop" and anything else means "go")?

IanfromRussia wrote:

Starlionblue wrote:

But let's take a step back for a moment. On a normal takeoff, you stay on centerline and rotate when the PM calls rotate. On a takeoff with an engine failure, you stay on centerline and rotate when the PM calls rotate.

Notice how there is no fundamental difference besides more input being required to stay on centreline.

The manual says that above 100 knots the captain should be "go-minded".

STOP. I was taught, even as an aeronautical engineer, that one has to abort if the engine fails before V1 and to take off if it happens after V1. The same basically tells Boeing in their manuals (and I suspect that Airbus too). I understand that there may be a grey zone near V1 where You still can take off with somewhat reduced clearance over the runway threshold, and that the actual runway length vs the balanced one may alter the situation. But I'm talking about situation where the captain has to abort if the engine just has failed but should (or even must) go if it hasn't, so the critical task is to recognize the event. And so my question is: should (generally speaking) the captain abort if he has just two cues: pronounced yawing tendency and the sound of master warning (provided that the speed is such that a failed engine means "stop" and anything else means "go")?

I think as you approach V1 you do enter a bit of a gray area as you may find that the engine failure is not an instantaneous event - you may have the beginning of rollback at, say, V1-10 or 15, but by the time you either notice the rollback or are alerted to the issue, you are so close it is very borderline. I see it as, if you have a chance to actually abort the takeoff, IE engines to idle, full RTO autobrake and spoilers before V1, go for it, but if you hit it right on the V1 cue you may be in for an interesting day. The other thing to think about is the difference between V1 and Rotate, which on a longer runway or lower weights might be enough to certainly reject, but if V1 and Rotate are so close together as to be almost the same, it really seems safer to take the issue into the air and then deal with it.

IanfromRussia wrote:

Starlionblue wrote:

But let's take a step back for a moment. On a normal takeoff, you stay on centerline and rotate when the PM calls rotate. On a takeoff with an engine failure, you stay on centerline and rotate when the PM calls rotate.

Notice how there is no fundamental difference besides more input being required to stay on centreline.

The manual says that above 100 knots the captain should be "go-minded".

STOP. I was taught, even as an aeronautical engineer, that one has to abort if the engine fails before V1 and to take off if it happens after V1. The same basically tells Boeing in their manuals (and I suspect that Airbus too). I understand that there may be a grey zone near V1 where You still can take off with somewhat reduced clearance over the runway threshold, and that the actual runway length vs the balanced one may alter the situation. But I'm talking about situation where the captain has to abort if the engine just has failed but should (or even must) go if it hasn't, so the critical task is to recognize the event. And so my question is: should (generally speaking) the captain abort if he has just two cues: pronounced yawing tendency and the sound of master warning (provided that the speed is such that a failed engine means "stop" and anything else means "go")?

As 77west says, it may not be that clear cut. Sure, you have two cues, but time is passing and you're rolling towards the end at a fair clip at this point. You not only have to recognize the indications, but also react. By the time you do that, you may be twenty knots faster. And again, engines don't always go bang and instantly stop producing thrust.

There are nuances.

Starlionblue wrote:

IanfromRussia wrote:

Starlionblue wrote:

But let's take a step back for a moment. On a normal takeoff, you stay on centerline and rotate when the PM calls rotate. On a takeoff with an engine failure, you stay on centerline and rotate when the PM calls rotate.

Notice how there is no fundamental difference besides more input being required to stay on centreline.

The manual says that above 100 knots the captain should be "go-minded".

STOP. I was taught, even as an aeronautical engineer, that one has to abort if the engine fails before V1 and to take off if it happens after V1. The same basically tells Boeing in their manuals (and I suspect that Airbus too). I understand that there may be a grey zone near V1 where You still can take off with somewhat reduced clearance over the runway threshold, and that the actual runway length vs the balanced one may alter the situation. But I'm talking about situation where the captain has to abort if the engine just has failed but should (or even must) go if it hasn't, so the critical task is to recognize the event. And so my question is: should (generally speaking) the captain abort if he has just two cues: pronounced yawing tendency and the sound of master warning (provided that the speed is such that a failed engine means "stop" and anything else means "go")?

As 77west says, it may not be that clear cut. Sure, you have two cues, but time is passing and you're rolling towards the end at a fair clip at this point. You not only have to recognize the indications, but also react. By the time you do that, you may be twenty knots faster. And again, engines don't always go bang and instantly stop producing thrust.

There are nuances.

Let me than put it so:
what might be the most benign and the least complete combination of sensory cues related to engine failure that would persuade You to abort past 100 kts on a runway just long enough for Your weight?

And what set of steps of verification You would accept as an appropriate trade off between the need to positively identify the event really requiring abort and the need for ugent expediency (given that both the failure to timely abort with an engine failing at an unfavourable speed and an RTO with a blown tyre and the both engines operating are likely to result in an overrun)?

IanfromRussia wrote:

STOP. I was taught, even as an aeronautical engineer, that one has to abort if the engine fails before V1 and to take off if it happens after V1.

This is incorrect.

V1 is the speed that first actions to commence a RTO has to be commenced.

The actual engine failure would happen a few seconds earlier than V1.

At V1 we remove our hand off the thrust levers so we cannot take actions to do a RTO.

zeke wrote:

IanfromRussia wrote:

STOP. I was taught, even as an aeronautical engineer, that one has to abort if the engine fails before V1 and to take off if it happens after V1.

This is incorrect.

V1 is the speed that first actions to commence a RTO has to be commenced.

The actual engine failure would happen a few seconds earlier than V1.

At V1 we remove our hand off the thrust levers so we cannot take actions to do a RTO.

Perhaps I oversimplified it, but what Your are saying isn't 100% correct either. If one of Your engines failed at 40kt and You have managed to reflect on it philosophically until You are beyond V1, that doesn't mean that the best course of action is to continue the take-off. If You passed V1 at 100 ft before the threshold all You can do is to try to decelerate as much as You can prior to the overrun.
V1 is the highest speed to commence the RTO without overrunning the runway provided that You have lost an engine (if You initiate RTO at V1 with all engines running You are going to overrun anyway even with use of the both thrust revesers). And if I remember my textbooks correctly, V1 is also the lowest speed You can have an engine failure at and still be able to attain 15 m (~50ft) over the threshold. Boeing says that if it fails 1 second before V1 and You initiate RTO just at V1 than You will have 35 ft over the threshold, and I believe that it is consistent with what I remember.

IanfromRussia wrote:

zeke wrote:

IanfromRussia wrote:

STOP. I was taught, even as an aeronautical engineer, that one has to abort if the engine fails before V1 and to take off if it happens after V1.

This is incorrect.

V1 is the speed that first actions to commence a RTO has to be commenced.

The actual engine failure would happen a few seconds earlier than V1.

At V1 we remove our hand off the thrust levers so we cannot take actions to do a RTO.

Perhaps I oversimplified it, but what Your are saying isn't 100% correct either. If one of Your engines failed at 40kt and You have managed to reflect on it philosophically until You are beyond V1, that doesn't mean that the best course of action is to continue the take-off. If You passed V1 at 100 ft before the threshold all You can do is to try to decelerate as much as You can prior to the overrun.
V1 is the highest speed to commence the RTO without overrunning the runway provided that You have lost an engine (if You initiate RTO at V1 with all engines running You are going to overrun anyway even with use of the both thrust revesers). And if I remember my textbooks correctly, V1 is also the lowest speed You can have an engine failure at and still be able to attain 15 m (~50ft) over the threshold. Boeing says that if it fails 1 second before V1 and You initiate RTO just at V1 than You will have 35 ft over the threshold, and I believe that it is consistent with what I remember.

OOOPS
Of course IF YOU DON'T INITIATE RTO

IanfromRussia wrote:

Perhaps I oversimplified it, but what Your are saying isn't 100% correct either. If one of Your engines failed at 40kt and You have managed to reflect on it philosophically until You are beyond V1, that doesn't mean that the best course of action is to continue the take-off. If You passed V1 at 100 ft before the threshold all You can do is to try to decelerate as much as You can prior to the overrun.
V1 is the highest speed to commence the RTO without overrunning the runway provided that You have lost an engine (if You initiate RTO at V1 with all engines running You are going to overrun anyway even with use of the both thrust revesers). And if I remember my textbooks correctly, V1 is also the lowest speed You can have an engine failure at and still be able to attain 15 m (~50ft) over the threshold. Boeing says that if it fails 1 second before V1 and You initiate RTO just at V1 than You will have 35 ft over the threshold, and I believe that it is consistent with what I remember.

If you have an engine failure at 40 kts and don’t immediately bring the thrust back on the other engines the only place you are going is off the side of the runway. The yaw is significant at low speed, and there is not enough steering authority to keep it straight on one engine at takeoff thrust. At higher speeds aerodynamic rudder authority is available.

V1 is never near the end of the runway, it has to be far enough away for the aircraft to come to a stop and then that distance has a buffer applied.

Stopping at V1 should not result in an overrun.

See https://skybrary.aero/articles/v1

zeke wrote:

IanfromRussia wrote:

Perhaps I oversimplified it, but what Your are saying isn't 100% correct either. If one of Your engines failed at 40kt and You have managed to reflect on it philosophically until You are beyond V1, that doesn't mean that the best course of action is to continue the take-off. If You passed V1 at 100 ft before the threshold all You can do is to try to decelerate as much as You can prior to the overrun.
V1 is the highest speed to commence the RTO without overrunning the runway provided that You have lost an engine (if You initiate RTO at V1 with all engines running You are going to overrun anyway even with use of the both thrust revesers). And if I remember my textbooks correctly, V1 is also the lowest speed You can have an engine failure at and still be able to attain 15 m (~50ft) over the threshold. Boeing says that if it fails 1 second before V1 and You initiate RTO just at V1 than You will have 35 ft over the threshold, and I believe that it is consistent with what I remember.

If you have an engine failure at 40 kts and don’t immediately bring the thrust back on the other engines the only place you are going is off the side of the runway. The yaw is significant at low speed, and there is not enough steering authority to keep it straight on one engine at takeoff thrust. At higher speeds aerodynamic rudder authority is available.

You've made a point!

zeke wrote:

IanfromRussia wrote:

V1 is never near the end of the runway, it has to be far enough away for the aircraft to come to a stop and then that distance has a buffer applied.

Stopping at V1 should not result in an overrun.

See https://skybrary.aero/articles/v1

Stopping at V1 shall never result in an overrun if You've been accelerating at normal take-off power up to a certain point before V1, have had an engine failure at this point and now initiate the RTO at V1. But if You lost an engine earlier You have to travel more distance to V1 while the distance to stop is the same, so You're going to overrun.

Take-off is engineered, in the latest Part 25 amendment, to accelerate on all engines to Vef (engine failure), one second of recognition at OEI acceleration (that distance), taken the first action to begin the RTO at V1, come to a stop within the available runway. That plan does not overrun. Vef must be not less than Vmcg, anything below Vmcg and the plane will rapidly veer off the runway if prompt reduction in thrust doesn’t happen.

If you lost an engine earlier, you stop, not attempt to continue even if directional control were possible. At Vmcg, it takes all of the available rudder. Remember Vmcg is based solely on aerodynamic controls.

I suggest you find a copy of Boeing Jet Transport Methods for reference.

GalaxyFlyer wrote:

Take-off is engineered, in the latest Part 25 amendment, to accelerate on all engines to Vef (engine failure), one second of recognition at OEI acceleration (that distance), taken the first action to begin the RTO at V1, come to a stop within the available runway. That plan does not overrun. Vef must be not less than Vmcg, anything below Vmcg and the plane will rapidly veer off the runway if prompt reduction in thrust doesn’t happen.

If you lost an engine earlier, you stop, not attempt to continue even if directional control were possible. At Vmcg, it takes all of the available rudder. Remember Vmcg is based solely on aerodynamic controls.

I suggest you find a copy of Boeing Jet Transport Methods for reference.

That's just what I'm saying. Even at speeds above Vmcg but well below the nominal Vef one is going to overrun if one delays the breaking until V1.

IanfromRussia wrote:

GalaxyFlyer wrote:

Take-off is engineered, in the latest Part 25 amendment, to accelerate on all engines to Vef (engine failure), one second of recognition at OEI acceleration (that distance), taken the first action to begin the RTO at V1, come to a stop within the available runway. That plan does not overrun. Vef must be not less than Vmcg, anything below Vmcg and the plane will rapidly veer off the runway if prompt reduction in thrust doesn’t happen.

If you lost an engine earlier, you stop, not attempt to continue even if directional control were possible. At Vmcg, it takes all of the available rudder. Remember Vmcg is based solely on aerodynamic controls.

I suggest you find a copy of Boeing Jet Transport Methods for reference.

That's just what I'm saying. Even at speeds above Vmcg but well below the nominal Vef one is going to overrun if one delays the breaking until V1.

Until AFTER V1...

As Zeke says there is a buffer. We're not perfect and neither are the weather reports.

You don’t understand Vef and V1 are very close, one second apart. Depending on weight Vmcg may be long past at Vef and V1. The data considers that distance. You’re not over running IF you have taken the first step to stopping by V1 and that presupposes a limiting runway. Any excess runway is cushion.

IanfromRussia wrote:

But if You lost an engine earlier You have to travel more distance to V1 while the distance to stop is the same, so You're going to overrun.

No you commence the stop as soon as the engine failure is recognised, you don’t wait to accelerate to V1 to commence stopping.

zeke wrote:

IanfromRussia wrote:

But if You lost an engine earlier You have to travel more distance to V1 while the distance to stop is the same, so You're going to overrun.

No you commence the stop as soon as the engine failure is recognised, you don’t wait to accelerate to V1 to commence stopping.

Surely!

IanfromRussia wrote:

zeke wrote:

IanfromRussia wrote:

V1 is never near the end of the runway, it has to be far enough away for the aircraft to come to a stop and then that distance has a buffer applied.

Stopping at V1 should not result in an overrun.

See https://skybrary.aero/articles/v1

Stopping at V1 shall never result in an overrun if You've been accelerating at normal take-off power up to a certain point before V1, have had an engine failure at this point and now initiate the RTO at V1. But if You lost an engine earlier You have to travel more distance to V1 while the distance to stop is the same, so You're going to overrun.

I don't see where you're going with this.

Whatever happens, you should initiate a reject before V1 if you want to be certain of stopping in time.

Starlionblue wrote:

IanfromRussia wrote:

zeke wrote:

Stopping at V1 shall never result in an overrun if You've been accelerating at normal take-off power up to a certain point before V1, have had an engine failure at this point and now initiate the RTO at V1. But if You lost an engine earlier You have to travel more distance to V1 while the distance to stop is the same, so You're going to overrun.

I don't see where you're going with this.

Whatever happens, you should initiate a reject before V1 if you want to be certain of stopping in time.

Surely.
I just mean that rejecting before V1 is necessary but not sufficient for stopping in time. On also must reject expediently even if there is some time to V1.

Thanks to everybody! )
Can now anybody advise me whether it is in the limits of human capability to retard throttles quick enough to stay on the runway if an engine seizes (not just spools down!) at or just before Vmcg?
Specifically, in the cases 1) if the runway is 1) dry and 2) if it is wet?

IanfromRussia wrote:

Thanks to everybody! )
Can now anybody advise me whether it is in the limits of human capability to retard throttles quick enough to stay on the runway if an engine seizes (not just spools down!) at or just before Vmcg?
Specifically, in the cases 1) if the runway is 1) dry and 2) if it is wet?

Yes, it is within the limits of human capability. Otherwise, the aircraft would not be certified. There's verbiage like "pilot of normal skill" or something in the regs.

Vmcg would change depending on whether the runway is wet, dry, or contaminated. Either way the aircraft must be manageable.