Engine failure at rotation

[Nicholas49]

Hello

Can I ask a couple of questions about engine failures?

I understand that twin-engine passenger aircraft must be certified to fly on one engine in the event of an engine failure, including at a critical stage of flight such as on take-off. I dare say that an engine failure at rotation is more 'pressing' (if I can put it that way) than one that occurs at FL390, although both are obviously important events!

I wanted to ask specifically about an engine failure on rotation.

1) Is this a more critical time to have an engine failure than on final approach? I was told on another thread some time ago that even if an engine fails on approach, the autopilot can maintain the ILS and the approach can be continued.

2) I understand every take-off is always flown manually, so if an engine fails at rotation, must the pilot manually alter the take-off configuration (I mean reduce the rate of climb, increase engine thrust on the remaining engine etc.)?

3) Is there a specific correction, trained for in the simulator, which is required for that aircraft type? In other words, both pilots know exactly what changes the PF will make to handle the situation? For example, a reduction from an initial 2,000 fpm climb to 500 fpm? (Realise that may be completely wrong!)

No need to explain V1 etc. - I'm aware of that - I'm just interested to know what actually happens if, as you pull back on the stick, an engine fails.

Thanks as always for your answers and apologies for any muddled terminology.

[kenparry]

Engine failure on take-off is critical. From the performance point of view, the most critical time is at V1, but that is not usually difficult as a handling exercise (mine were all in the sim, happily my count in the real thing is a nice fat zero). At rotate, as you suspect, it can be more difficult, simply because tha aircraft is no longer restrained by the ground to stay wings level. With any twin, especially with swept wings which exaggerate it, the initial yaw will be followed by roll into the dead engine unless you do something. The best "something" is enough rudder to stop the yaw and enough aileron to return to wings level.

What you then aim to do is climb out at V2 and whatever rate of climb that gives you. There is no need to increase power; the performance calculations for any derated take-off account for obstacle clearance at the reduced power. The standard teaching is fly, navigate, communicate as the order of priorities. All companies have SOPs that cover these things, and the course of action in the event of engine failure is covered in the pre-take-off briefing; that will not cover the above handling points, but things such as flap retraction altitude, any route change as a result of losing the engine (often called emergency turn) and intentions as to where to land, which might be the departure field or might be another depending on weather, runway length, and other factors.

All my airline flying was Boeing, and yes, all that phase was always hand flown. Airbus 320 & later is a bit different, as the flight control system does some things that on other types are more like autopilot functions - but you will have to ask someone with relevant experience about that.

[SNS3Guppy]

Nicholas,

Takeoff configuration means the way the airplane is set up with respect to flaps, leading edge devices, etc. When an engine fails, no configuration changes are made.

Where the takeoff is flown manually, one simply flies the airplane. No big changes, nothing different except some rudder input to offset the assymetric (uneven) thrust. The takeoff continues just as it did before, but things will happen a little slower. Reaching the takeoff safety speed of V2 will take a little longer. One's final climb pitch angle will be shallower than the pitch angle with both engines operating, and the climb rate will be less.

Normally with an engine out, nothing is done until at least 400'. At some airports, a turn procedure is prescribed, and other than a radio call to notify the tower or departure control that the crew is handling the problem (and to announce an emergency, where applicable), little else is done. The airplane will typically level off or reduce climb to begin cleaning up, and then continue climbing while flying either a departure procedure, vectors to return to land, or a designated engine-out procedure ("turn procedure"). During this time, once cleaned up (configured for the climb), the appropriate checklists will be run, abnormal or emergency checklists will be run, the engine secured or other problems addressed, and a preparation made to take the next step. In most cases, the next step will be a return for landing.

In that event, generally a check of weather will determine that we can indeed return, we'll need to dump fuel, we'll begin that process, brief the approach, get a clearance, and return to land.

The takeoff process with the engine out isn't much different than with the engine running. It's just a little (or a lot, depending on the airplane and the amount of thrust used) rudder, and straight, simple flying the airplane.

In our operation, we never engage the autopilot until our flaps are up (configured for the climb, or "cleaned up"), so the entire evolution is hand-flown.

Yes, engine-out on takeoff is the most critical time for an engine failure.

The engine-out doesn't need to be at rotation; it can occur at or any time after V1. The takeoff will still continue to the preplanned rotation speed, and the climb-out will be at V2.

[Neptunus Rex]

Nicholas49,

Where the takeoff is flown manually,

I think that was just an error of grammar. To avoid any confusion, in all airliners, the take-off is always flown manually.

Given the appropriate equipment in the aircraft, as well as on the runway, we can perform automatic landings. To date, no airliner in service is capable of an automatic take-off.

[JWP1938]

"To date, no airliner in service is capable of an automatic take-off."

Speaking as SLF with just a couple of flying lessons I find that interesting. Apart from ensuring the ground/flight path is unobstructed I would have thought that automatic takeoff would be easier to program than landing. Obviously ensuring nothing is in the way must be done manually, or is that why?

[Nicholas49]

Thank you for the replies.

It is interesting to read that not much changes, apart from rudder input. I find it very interesting, and reassuring, that the certification for engine failure on take-off means there is no need for quick, corrective action to avoid a dangerous situation developing. They're clever, those people at Boeing and Airbus.

Couple of follow-up questions, if I may.

If, as you say, the pilot does not reduce the angle of attack or increase thrust after the engine failure, am I right in thinking the aircraft will however accelerate more slowly given the reduced engine thrust?

Am I also correct in thinking that the engine failure certification and take-off performance calculations ensure that, even if you do not reduce the angle of attack, there is no chance that the speed will stick at Vr or even decay towards a stall?

In your simulator training, do you need to train for and practise engine failure at V1 and Vr separately, or is the rudder input sufficiently similar that if you can handle one situation, you can handle both?

NR: Thanks for the clarification. Yes, I'm aware all take-offs are flown manually.

[Lord Spandex Masher]

Nicholas it's not the AoA that we need to reduce, that'll be the same for a given airspeed (V2 in this case) regardless of the number of working engines. We need to reduce the angle of climb to ensure that we can maintain the correct airspeed.

I can't answer your question about the certification process but suffice to say that an aeroplane will not climb at the same angle on one engine as it would on two. For instance, the usual climb angle, initially, would be round about 15-20 degrees, for a single engine case you'd be looking at about 5 degrees to maintain your airspeed. If we try and climb at the normal angle then the airspeed will quite quickly reduce to and below V2 (assuming we did nothing about it) and then you will find yourself in all sorts of bother.

Edit: In the case of a failure at V1 or Vr it is essentially the same process. V1 would be the worst case as it is the lower airspeed and would require a greater rudder input. However, generally there is very little difference between the two speeds (although I have seen a difference of 25kts between the two speeds). If you have an engine failure at V1 then you control the aircraft with the rudder and continue to accelerate on the runway to Vr before you rotate.

[canyonblue737]

From a performance perspective losing an engine at V1 is most critical and will result in the most runway used and lowest obstacle clearing heights. From a pilot perspective a failure at rotation can be a bit more of a handful since the airplane in flight rolls and yaws as a result of the failure. In general with all aircraft using significant rudder to prevent the yaw combined with lowering the nose from a standard climb pitch to prevent decay of airspeed will result in a positive rate of climb and when at a safe altitude other procedures can be accomplished. Adding power on the good engine and in prop aircraft confirming feathering might also need to be done right after the failure but most jet aircraft have performance calculations for each takeoff that do not require pilots to add power to the good engine in the event of a failure.

I suffered my one and only engine failure at rotation with the nose wheel in the air but mains still on the ground. It was a contained failure of an interstage turbine on a turboprop but handling was fairly docile and I never felt in jeopardy. Our normal climb rate would have been 2500+ feet per minute but we managed just under 500 fpm as we climbed to pattern altitude and returned to the field. I currently fly the Boeing 737 and it would be even more docile with less pilot pilot workload and more performance should the same occur.

[SNS3Guppy]

I think that was just an error of grammar. To avoid any confusion, in all airliners, the take-off is always flown manually.

It wasn't a grammatical error, though perhaps the use of "Whereas" would have made the point more clear.

It is interesting to read that not much changes, apart from rudder input. I find it very interesting, and reassuring, that the certification for engine failure on take-off means there is no need for quick, corrective action to avoid a dangerous situation developing. They're clever, those people at Boeing and Airbus.

I don't think any reply indicated that quick corrective action isn't required; if one doesn't use rudder, the airplane may depart the runway. Depending on the point at which the takeoff is continued or rejected, decisive action is required to meet the necessary calculated performance. If one experiences the engine failure prior to or near V1 and rejects, no delay should be had in executing the rejected takeoff. Timely use of braking, speed brakes, reverse, etc, are very important (though the stopping distance isn't predicated on reverse). If one continues, then decisively continuing, rather than hesitating or diverting one's attention is also required. The engine loss on takeoff profile doesn't allow one to be a spectator; a potentially dangerous situation has already developed. Proper action is required to prevent it from becoming any worse.

Yes, the folks at Boeing and Airbus (and Embraer and McDonnel Douglas, etc) are clever. More clever than or as clever as the rest of us, anyway.

If, as you say, the pilot does not reduce the angle of attack or increase thrust after the engine failure, am I right in thinking the aircraft will however accelerate more slowly given the reduced engine thrust?

If the engine fails at V1, there's no angle of attack to reduce. If it fails with the nose already in the air, one doesn't do a thing; one pitches through the rotation, albeit slower than normal, and flies off at and maintains V2.

Increasing thrust sets the takeoff calculations out of balance. The takeoff numbers, specifically V1, Vr, and V2 are predicated on the preplanned power numbers. If these are altered, the numbers are invalidated. When we calculate takeoff power, we do so with an engine failure in mind. Increasing power increases the assymetrical thrust imbalance, and one may find one's self short of rudder. No need to reduce angle of attack or increase thrust. The airplane has adequate climb performance after takeoff, as calculated in advance, to meet the obstacle climb gradient criteria and escape mother earth. This only applies to transport-category aircraft, of course.

Am I also correct in thinking that the engine failure certification and take-off performance calculations ensure that, even if you do not reduce the angle of attack, there is no chance that the speed will stick at Vr or even decay towards a stall?

When I review the takeoff data, I look at the power setting and the criteria that were used to determine it. I look at the preplanned pitch angle. We have a 10 degree limit on rotation; above that we risk a tail strike, so if we reach 10 degrees and it's not off the ground, we've probably rotated too quickly, and we hold it there until it comes off. My takeoff calculations also include a target pitch atttitude after takeoff; this pitch attitude should hold my target V2 speed with an engine out. With all engines operating, I should be pitching a little more than the target, but the calculations are always planned with an engine-loss during the takeoff at some point.

If the airplane isn't accelerating at all, if it's not going to fly, then something more than a powerplant failure may be occurring, and one may have no choice but to reject the takeoff.

In your simulator training, do you need to train for and practise engine failure at V1 and Vr separately, or is the rudder input sufficiently similar that if you can handle one situation, you can handle both?

We train for engine failures before V1, and after V1. When the failure occurs after V1 isn't significant; our concern is whether we're going to reject the takeoff, or continue. Continuing is safest, but if a failure occurs shortly before V1 is called, we may have insufficient runway or ability to accelerate to Vr or V2, and therefore the takeoff is rejected. Whether an engine failure occurs at V1 or at Vr isn't really a concern; so long as we know the decision to continue the takeoff is happening, it's all the same, really.

There really isn't a "both," because it's the same situation. An engine failure after V1.

Yes, we do practice and train for engine failures at various times during the takeoff, including various times before V1, and various times after V1. If it's before V1, it's a rejected takeoff, and if it's after V1 and the airplane is still capable of going flying, then it's a continued takeoff, with no significance between the engine failing at V1 or at VR, or any time thereafter.

[mutt]

If it's before V1, it's a rejected takeoff,

Do you use actual runway limited takeoff weights for this? Last time we tried this in a classic simulator, we never stopped before the end of the runway

[Nicholas49]

Thanks for the replies.

I think I may have confused Angle of Attack and climb pitch. I thought they were the same thing. It appears not.

So just so I have this clear, the corrective action you would take with a failure at rotation is: rudder input to keep the aircraft flying straight and lowering the nose to keep your airspeed from decaying and ensure you accelerate to V2?

This is probably a daft question, but I wonder how you establish by how many degrees to lower the nose to maintain the airspeed and accelerate to V2? Is it a question of feel, experience on, knowledge of, and simulator training for your particular aircraft type, or do the aircraft's systems (e.g. Flight Director) provide guidance?

[Lord Spandex Masher]

You've almost got it. Google will help you with AoA and climb angle.

It's not so much a case of lowering the nose but a case of rotating slowly, remember we are still on the runway at that point. Most modern flight directors will command your speed to about V2 with an angine failure so it would be just a simple case of following that. However, we are allowed to dispatch with an inop flight director so in that case we would generally aim for an initial pitch angle of between 5-8 degrees, which should be there or thereabouts anyway, trim things out and watch the speed trend. From there it's the same as two engine flying except you have a lot less performance.

Of course practice and experience will help but sector to sector things like your weight and the weather will all change so speeds and pitch angles and performance will all be very slightly different.

[SNS3Guppy]

Do you use actual runway limited takeoff weights for this?

You betcha. So long as we're within the weight limit values for the runway, stopping shouldn't be a problem. Insofar as rejects in the simulator, we generally do max takeoff weight, but we do verify the stop distance against what's calculated (bearing in mind that it's a simulator and not the actual airplane).

In the real world, of course, we do the same; the runway-limited actual takeoff weight is used to calculate stopping distance from V1, and a stop margin is calculated off that. We anticipate stopping within the calculated distance, so long as we do our part.

I think I may have confused Angle of Attack and climb pitch. I thought they were the same thing. It appears not.

Angle of attack and pitch angle are never the same, except by coincidence. Angle of attack is the angle formed between the airstream as it arrives at the wing, and the mean aerodynamic chord of the wing (which changes with aircraft configuration. Angle of attack is different close to the ground ("ground effect) than in flight for a given pitch angle and airspeed, and angle of attack is different in flight for a given pitch angle and airspeed depending on flap and leading edge device position (aircraft configuration).

I understand where you're coming from; it's easier to envision angle of attack as a function of pitch, and to a certain extent that works for simple explanations. It doesn't work if you want to expand beyond a simple explanation, though.

Angle of attack isn't just the angle between the pitch of the airplane, and the free airstream; the pitch of the airplane isn't the same as the angle of incidence, which is the angle the wing is set relative to the longitudinal axis of the airplane. Even head-on into the wind, the airplane normally has a positive angle of attack of several degrees. That's because the chord line of the wing, specifically the aerodynamic chord line of the wing, is set at a different angle than the long axis of the airplane. This means that the chord line (the line between the leading edge of the wing and the trailing edge of the wing, to make it simple, is different than the line formed from the front end of the airplane to the back. That difference is the "angle of incidence," and it's significant here because as the airplane sits, without the pilot doing anything, the angle of attack is always different than the pitch angle.

The angle of attack is further modified because of the way air approaches the wing. Behind the wing air is forced down, the measure of which is lift. We call that "downwash," and ahead of the wing air is given an upward vector, called "upwash." This local flow, or upwash, affects the angle of attack. As you can imagine, air angled upward from ahead of and below the wing creates an even bigger angle to the chordline of the wing than the free airstream. This is more pronounced when slow and "dirty," when flaps and leading edge devices are extended.

Angle of attack, then, changes with aircraft configuration and airspeed. As you're imagining it, however, the most direct control over angle of attack is the pilot's pushing forward or pulling back on the control column or stick. Pitching up and down also influences angle of attack. To confuse you a little more, an airplane in cruise might have a power reduction made, and begin a descent, but see little change in angle of attack, even though the nose may be pointed down more; the angle of attack sometimes changes with pitch, but other times it doesn't, or doesn't change in proportion to pitch changes.

It may be easier to think in terms of pitch for now, however, relative to the questions you're asking.

So just so I have this clear, the corrective action you would take with a failure at rotation is: rudder input to keep the aircraft flying straight and lowering the nose to keep your airspeed from decaying and ensure you accelerate to V2?

Rudder input, yes. Lowering the nose, no. The crux of your question appears to be what to do if the nose is in the air (in other words, we've reached rotation speed, and have pulled back on the control column, raising the nose into the air, as we prepare to take off) and we experience an engine failure.

The short answer is we fly the airplane, or whatever portion of it is already flying. Rudder to keep the airplane going straight down the runway and under control, and keep the pitch attitude. Rotation speed and the climb pitch attitude has already calculated with an engine failure in mind. We don't need to touch the power, we don't need to drop the nose back down; we've already reached the rotation speed that we calculated earlier. We're there.

We have already rotated at that speed, and it's enough. In the airplane I fly, we stop the rotation at 10 degrees until we are off the ground and have a positive climb going. Then we can continue to pitch up.

We've reached V1. We've reached Vr. We've rotated, and we're waiting to come off the ground. We're not going to lower the nose back down. If we do that, we're going to dump lift. We don't want that. We want to go fly. We may be very runway-limited, and we're looking to get off the ground now, and get away from obstacles so we can deal with our new problem.

Our next concern is achieving and holding V2. This is our takeoff safety speed, and it's predicated on the engine-out climb at our previously calculated power settings, minus an engine. My employer's policy is to make the climb at V2; however, if we've passed through V2 (due to a slow rotation, perhaps, or we're just accelerating faster than we thought, or we had already achieved a higher speed when the engine failed), we can hold up to V2 plus 10 knots, as we climb.

At this point, we do control airspeed with pitch. We're looking for V2; if we're not getting there quickly, we'll hold our pitch attitude while we accelerate. If we pass through V2 and the airplane wants to keep accelerating, then we're going to increase our pitch to keep our speed at V2.

This is probably a daft question, but I wonder how you establish by how many degrees to lower the nose to maintain the airspeed and accelerate to V2?

None, Nicholas. There's no need. If we've already reached Vr and have rotated, then we're not going to put the nose back down; we've already met the speed requirement, and we know we can continue at this weight. There are rare, and unusual exceptions, such as windshear on the takeoff which might cause the airspeed increase to stagnate or fall back. We're past V1, and we're going flying. We're going to hold our pitch attitude and look for V2. The airplane will probably be off the ground before we reach that point, anyway.

It's not really a matter of lowering the nose as it is rotating a little more slowly. If the engine failure occurs just after V1, before Vr,then rotate slower. If the engine failure occurs during Vr, with that speed already met and the airplane being rotated to the precalculated altitude, we've already got the necessary speed. Time to go fly.

Is it a question of feel, experience on, knowledge of, and simulator training for your particular aircraft type, or do the aircraft's systems (e.g. Flight Director) provide guidance?

I'm not really looking at the flight director, at this point. I'm noting my airspeed and my pitch. I'm consciously rotating slower; if I normally rotated in six seconds, this time I might take nine. I'm noting my airspeed and my pitch attitude. I'm keeping a visual reference outside on the runway centerline and transitioning in and out to my instrumentation. Once Vr has arrived, I'm in and out of the cockpit, mostly in, looking to keep the airplane straight and put the "pipper" on the attitude indicator on top of my 10 degree nose-up line. I'll be stopping there until the airplane comes off the ground, and about that time I should be close to V2. I'll continue increasing my pitch to hold V2, to the preplanned target pitch attitude established as part of the takeoff calculations. I'll vary that pitch just slightly to hold V2, as necessary.

From there, we'll be climbing to a pre-calculated engine-out altitude (again calculated as part of our departure preparations), where I'll be leveling off an cleaning up (flaps up) as I accelerate to my clean climb speed. Then climb will continue.

Big airplanes can be felt, a little, but they're largely numbers airplanes. Calculate the right numbers, and and most of the time the performance (at least in our equipment) comes out extremely close, if not on. Knowing how much to rotate and pitch is largely a matter of training and calculations; we have the numbers in front of us. The climb is mostly about flying the airplane (as opposed to letting it fly us) and using the numbers that we've calculated that will allow the airplane to do what it's certified to do.

[oversteer]

Is gear retraction critical to a successful 'getaway' ?

I only ask because it apparently was for Concorde (which at that point had lost 1 of 4 but could not accelerate or climb) - I wonder if it's the same for today's commercial aircraft

[KBPsen]

Is gear retraction critical to a successful 'getaway' ?

It depends. On my current aircraft the reduction in performance, should the gear not retract, is equivalent to approximately 20 tonnes of additional weight.

With all engines operating that will usually not present a problem, but with an engine out it can be a problem.

[Nicholas49]

Sorry that I'm a bit late coming back to this.

Thanks for the follow-up replies, gents.

I have a much clearer picture of what happens now. Unsurprisingly, it's even safer than I initially thought. And you've put straight a fair few incorrect assumptions on my part!

[SNS3Guppy]

Is gear retraction critical to a successful 'getaway' ?

Generally speaking, yes, but in some aircraft retracting the landing gear increases drag. Gear doors open, and the motion of the landing gear increases, rather than decreases drag.

In transport category aircraft, the takeoff is divided into "segments," each of which prescribe minimum climb gradients. The "second segment" climb is often discussed, being one of the most critical, and begins with landing gear retraction, and continues to until 400' minimum.

The first climb segment begins 35' above the runway and lasts until the gear is retracted. The minimum climb gradient during this time only stipulates that a positive rate of climb be achieved in 2 engine aircraft, or .5% in 4 engine aircraft.

This is really the critical point in the takeoff; getting away from the ground and to an altitude where it's safe to begin cleaning up in order to climb.

[Airbus Girl]

Also to add:-

- when calculating speeds (V1/Vr) the performance is always based on losing an engine at V1, so is always "safe".

- most pilots do 6 monthly sim checks, and this always includes practice of engine out on take-off. It is a compulsory item. Usually a cut at V1, which may or may not be a heavyweight departure. We have to get it right, if you are outside of limits in your handling of it then you have to do it again. If you don't get it right the second time you fail. This includes maintaining the flight path (ie keeping straight), following the planned departure, handling the engine problem, notifying ATC if relevant (usually would be!), reaching acceleration altitude, cleaning up and then continuing in the climb to assigned (or requested) safe altitude.

- Airlines are moving over to a new sim regime, ATQP, and that is different to what I just said above!

[Exascot]

I should know the answer to this question but can't for the life of me remember or find the answer. OK, happy with 4 engine aircraft performance, climb segments, V speeds required, loss of one engine and acceptable critical time for the loss of a second. I explained this in layman's terms over a beer to a friend. Then he asked about a three engine aircraft . Can you lose two before the 4th segment or indeed at all before a safe level? Any assistance welcome please, he will owe you a beer.

[Nicholas49]

If you don't get it right the second time you fail.

That seems very harsh. Given that it is highly unlikely that you will encounter the failure while flying the line, and given that the last time you handled this scenario was six months ago, I wonder how exactly you are supposed always to get it right in the simulator? Do you get to practise the manoeuvre before you sit the simulator assessment?