A320 Single Engine flying - beta target indication [Archive]

WeekendFlyer

21st Jun 2013, 12:28

If I understand it corectly, the airbus FBW family have neutral APPARENT lateral stability, because the flight computers ensure the aircraft does not generate a roll rate unless the pilot tells it to by moving the stick left or right.

However, the airframe DOES have inherent lateral stability, due to wing sweep and dihedral among other factors. Therefore any sideslip induced by asymmetric thrust will cause a laterally stable response by the airframe, which the FBW computers have to cancel out using aileron and spoiler inputs. These cause additional drag, so you need to find the sideslip angle that gives the lowest combination of rudder drag and aileron/spoiler drag while maintaining a steady heading sideslip sufficient to counter the asymmetric thrust. This gives you the highest possible L/D ratio and thus the highest possible climb rate. This happy balance of control inputs is what the beta target is helping you to achieve.

As I see it, the key to a successful and not-too-scary OEI climb out, once speed is pegged to the optimum climb speed for the configuration, is to avoid unecessary sideslip as much as possible.

Regarding the flex issue, not entirely sure selecting TOGA rapidly is a good idea, it depends on the airspeed you have at the time and how good your climb rate is. The last thing you want to do in a low-speed OEI situation is rapidly exacerbate the thrust asymmetry and sideslip (which increases drag hugely) if you are only a few kts above the minimum control speed. IMHO any thrust increase on the remaining engine should be smooth and carefully controlled with matching rudder input so as to minimise sideslip excursions, which, if mismanaged, would certainly hurt your rate of climb and could even cause a speed reduction in the worst case.

Having said that, if selecting TOGA causes the beta taget to appear, then at least the aircraft will be helping you manage the sideslip. I can see Airbus's thnking on this, and it seems sensible. What is the usual SOP regarding TOGA use in this situation?

vilas

21st Jun 2013, 13:15

john smith & Weekendflyer
Although OEI performance is certified with Flex it is a good idea to select TOGA once you have centered Beta. In A320 with computers trying to resist the displacement it does not cause any prblems. A320 can be trimmed and flown hands and feet off. Flying the entire procedure in flex will take longer time to reach acceleration altitude and also to accelerate to green dot. Since the profile is related to terrain clearence it is better to be done with sooner than later. Also if you delay too much and select TOGA after SRS is changed to V/S0 the FMGS will go into GA mode.

vilas

21st Jun 2013, 14:07

John smith
Airbus training is not at all against TOGA. The first thing after gear up is"consider TOGA" (PRO-ABN-10 p1/14). Unlike your Airline there are others who advice to take TOGA as soon as engine fails however I am against that. You are not flogging the engine by selecting TOGA. The engine can withstand what is certified.

mcdhu

21st Jun 2013, 15:44

Guys, this discussion re TOGA or not after engine failure is a perennial one. Already some great points have been made in both directions.
As Vilas said, "consider" is the mantra. But so many times in the sim I see pilots forgetting to "consider" TOGA and so my personal SOP after trimming is:
AP1/2, HDG Pull, TOGA Thrust - I can always consider not selecting TOGA if I have a good reason. But why would you not want to double your rate of climb?

I hope you would all agree that pilots tend to rotate carefully and more slowly after an engine failure to avoid over-rotating and losing speed. So consider a bad day: wet runway, perf limited by a close in obstacle which you are going to clear by 15' (Okay, that's net). Because of the EF you have rotated slowly and so are already behind the expected performance profile. Additionally, you are now flying fast on V2 imp and so are experiencing more drag than expected. All in all, you are in bad shape. TOGA will help here!!

These are only my thoughts and I certainly have no intention of starting a tiddling competition over this but you are welcome to comment.

OPEN DES

21st Jun 2013, 17:57

Hi MCDHU,

Didn´t remember this thread.
Agree on everything.
N1 can definitely be lower than 80% on the A319´s with FLX. This will only occur at very high Flex temps though. Associated performance margins (spread between OAT and Tflex) will be such that beta-target and (conventional) sideslip indication both suffice for flying the a/c inside the envelope. So I would not select TOGA for the sole purpose of getting the blue target back!

IFLY_INDIGO

22nd Jul 2017, 14:04

Demand of thrust is highest during T/O
Engines run at high thrust level during T/O and airspeed is low.
If an engine fails at this time, other engine will cause excessive yaw due to assymetrical thrust. Yawing causes sideslip and increase in drag. Yaw damper will react to sideslip, but not enough. At Low airspeed, control surfaces are not very effective.
Pilot is required to give rudder input to stop the sideslip. Giving rudder input for zero sideslip will require too much rudder deflection.
It may be the case that even full rudder deflection is not enough to ceter the sideslip indicator or rise in drag is too much for available thrust to handle. Acceleration and climb performance will hamper.
Airbus found a 'sideslip compromise' which overall reduces the drag by limiting rudder deflection. This is indicated by blue beta target. This improves acceleration and climb.
This is the problem of low airspeed when large rudder deflection is required and drag increases drastically. On acceleration, this problem ends, hence when flaps are retracted normal sideslip indicator resumes.

john_tullamarine

23rd Jul 2017, 00:17

Yawing causes sideslip

Are you sure of that ? Most analyses would have it that, once the initial problem is under control (considered to occur instinctively for the trained pilot) and the aircraft is flying straight, it is the pilot rudder input causing the sideslip .. hence the need for some bank to reduce the sideslip in near Vmc situations.

Pilot is required to give rudder input to stop the sideslip.

Perhaps the rudder input is to control the asymmetric thrust yawing moment ? At low speed, where the concern is greatest, the relevant pilot input is to bank into the operating engine(s) to reduce sideslip... noting that some systems have a problem with small angles of bank so the sideslip has to be accommodated due to other considerations.

Giving rudder input for zero sideslip will require too much rudder deflection.

Perhaps you can explain just how rudder input can result in zero sideslip ? .. presuming wings level.

Airbus found a 'sideslip compromise' which overall reduces the drag by limiting rudder deflection.

I have no specific knowledge of how the indicator functions. However, I suggest that the idea is to reduce sideslip to a value somewhere near zero.

On acceleration, this problem ends, hence when flaps are retracted normal sideslip indicator resumes.

Or, perhaps, sideslip related drag is critical at low speed but, to a large extent, can be ignored at higher speed to reduce pilot manipulative workload ?

A question, though, from a non-AB pilot - do you conduct the initial climb out wings level or with some bank into the operating engine(s) ?

Vessbot

23rd Jul 2017, 01:51

The rudder of course always controls yaw, but our control of yaw has 2 separate jobs -- of controlling heading, and controlling sideslip. If the thrust is symmetrical, they are tantamount to the same thing, and we don't really think about it.

But with asymmetrical thrust, it starts to matter. Let's say we lose the right engine. If we do nothing about it, it wants to yaw right due to the thrust from the left side. So we naturally stop the right yaw with left rudder. The clockwise yaw torque from the thrust, is balanced by the counterclockwise yaw torque from the rudder. Therefore heading is steady.

But the rudder, in addition to producing a counterclockwise torque, is also producing a force to the right - with nothing to counter it. Therefore, we will drift to the right. Heading and direction of flight no longer match, which is a slip. That is why zero heading change no longer equals zero slip, as it does in normal flight. To fix this, we counter that rightward force with a leftward force: a horizontal component of the lift vector, obtained by banking slightly left. Now the left and right forces match, and nothing is pulling us sideways. Ergo, heading and flight patch match, and slip is zero. (But the ball is to the left).

But here's a crucial side effect - and the answer to John T's question. There's another contributor to the yaw torque on the plane, besides the rudder and the asymmetrical thrust. It's any sideways air hitting the back of the plane, i.e. the slip itself. It too must be countered with rudder to maintain a heading. Recall that in symmetrical-powered flight, it takes a constant rudder input to maintain a slip. Without it, the sideways-hitting air will turn the tail into the "new" direction and the slip will disappear.

Well, in our right-engine-out scenario, if we go back to the no-correction situation, the air will come from the right and yaw (and boat-turn) the plane to the right. So we need left rudder to prevent that. If we eliminate the slip by banking slightly left, this will disappear! If we bank more than the required amount to the left, we'll then slip the other way and will need right rudder. <-- But, the rudder inputs laid out in this paragraph are only for the slip; they're in addition to the rudder input for the asymmetric thrust. The actual rudder input is the sum of both. In case you're starting to get lost in the weeds (I am, in writing this) let's try a table format, with sample bank angles and made up "units" of rudder travel.

Condition ruder for rudder for total
ass. thrust slip rudder

No bank 5 5 10
2 deg. of bank 5 3 8
4 deg. of bank 5 1 6
6 deg. of bank 5 -1 4

I had to do weird things, and it still won't show up quite right.

Bottom line is, that the more you bank to the left, the less left rudder you need. You can get so much effective left yaw torque by banking, (at the cost of increasing drag) that you can artificially lower the Vmc. This is why the certification limit for Vmc is a maximum of 5 degrees of bank. Any more yaw authority must be obtained by rudder.

john_tullamarine

23rd Jul 2017, 04:11

Indeed, that's all fine and, largely, what I was suggesting in the earlier post.

So we need left rudder to prevent that ..

.. however, if one is at, or very near, Vmc, one doesn't have any left rudder remaining to play with .. else Vmc would have been lower (assuming we don't have to contend with rudder stall for instance). Indeed, if there is no bank, rudder becomes more limited and Vmc, necessarily, would be expected to increase. So what does AB suggest in that (near Vmc) situation ? Surely not to relax rudder ?

What one does at higher speeds, where rudder is not limiting, can be tweaked as might be desired. Wings level and a small loss in climb is a lot easier than trying to fly a couple of degrees wing down to get that last bit of climb. As to the final adjustment for drag, AB would have more than enough models and FT data to provide crew guidance via whatever beta indications.

For the AB, do you fly out OEI wings level or with favourable bank ?

Goldenrivett

23rd Jul 2017, 07:14

Hi John,
For the AB, do you fly out OEI wings level or with favourable bank ?

For minimum drag (no aileron or roll spoiler deflection) at VMCA, then you would need 5 degrees bank.
The problem with AB normal Law is that you can't "feel" when you have any aileron deflection and the only clue is the position of the Beta Target.

In the sim, with V2>VMCA (often by 10 kts or more), less accurate flying can result in level wings climb out with no clue to the amount of aileron deflection applied. SOPs require us to engage the AP early on to reduce the work load and rudder deflection is then controlled automatically. The aircraft will gradually centre the Beta Target resulting a few degrees of bank, often masked by heading changes.

Fast magazine issue 20 (http://www.aircraft.airbus.com/support-services/publications/?eID=maglisting_push&tx_maglisting_pi1%5BdocID%5D=41128)
"If an engine fails, the triangle at the top of the PFD horizon will divide (see Figure 2). The lower resulting trapezoid changes to blue and will move out in a similar sense to a conventional slip ball, indicating pilot rudder demand in exactly the same way. However, the function is significantly different from the ball in that the centering of the trapezoid (Beta Target) will provide maximum performance with minimum drag.

If no rudder action is taken to centre the Beta Target, like a conventional aircraft, roll will occur towards the dead engine. However, unlike a conventional aircraft, with stick free (no sidestick roll input), the flight control laws will detect the roll and apply aileron and spoiler to stop the roll. The rate of roll will depend on the severity of the thrust loss. In the worst case, the roll will stabilise between 7-9 degrees bank angle, leading to a slow heading drift of about 0.5 degree per second, without any sidestick roll input or rudder input."

john_tullamarine

23rd Jul 2017, 07:43

Thanks for that .. I'll wade through the details over a coffee or two later this evening.

However, the question still remains re bank. Your suggestion that

For minimum drag (no aileron or roll spoiler deflection) at VMCA, then you would need 5 degrees bank

doesn't make much sense to me. If you are after the standard bank angle, then that will require an aileron input.

I might be just a bit slow but I can't infer from your post if you target some bank or just go with wings level regardless of speed schedule ? I have some difficulty with any suggestion that wings level is the way to go when one is back near Vmc ... a 10kt margin can get swallowed up by the effect of no bank pretty quickly.

While this will vary with Type, some of the 4-engined machines can see a 40kt plus increase in Vmc if the bank is allowed to go the wrong way .. Real world Vmc is very sensitive to bank angle.

Goldenrivett

23rd Jul 2017, 17:46

Hi John,
If you are after the standard bank angle, then that will require an aileron input

With wings level and the rudder balancing the asymmetric thrust yaw, the aircraft will side slip due to the side loading of the rudder. The induced roll must be checked with aileron (and possibly roll spoilers).

With bank towards the live engines, an opposing side slip force can be generated (Weight * Sine(Angle of Bank)) and total side slip can now be reduced to zero resulting in no aileron required.

Hahn

23rd Jul 2017, 19:42

The bit of bank required on one engine is similar to a crosswind landing where a few degrees of bank counter the drift and the flight path is stabilised with the rudder. The bus is "sitting" nicely on the live engine and flies hands free with the rudder trimmed properly.

john_tullamarine

23rd Jul 2017, 22:38

With bank towards the live engines, an opposing side slip force can be generated

.. being the idea of having a bank input .. which, in turn, provides a lesser Vmc.. However, I suspect that, in the Vmc situation, there will be a residual slip remaining. At higher speeds, where one targets a lesser bank angle (typically around the 2-3 degrees mark) for OEI climb performance, that may not be the case.

vilas

24th Jul 2017, 04:08

With OEI if an aircraft is trimmed for zero side slip it will have some drag due to side loading. The minimum drag position is some slip neutralised by some bank. But how much?Airbus does the calculation for the pilot by creating the beta target which leaves some slip. Pilot just trims the rudder and flies the heading with side stick. This is the minimum drag for optimum OEI performance. Yes as John pointed out there is no bank without aileron but still it is the least drag position.

Goldenrivett

24th Jul 2017, 06:41

vilas The minimum drag position is some slip neutralised by some bank
.... Yes as John pointed out there is no bank without aileron
I think we are all saying something similar, but using the wrong words.

Slip is usually displayed using a heavy ball (pea) in a "U" tube (which works well for symmetrical thrust flight.) However aerodynamic slip is better measured using streaming lengths of wool across the canopy.

During steady asymmetric flight with rudder balancing yaw and bank towards the live engines to counteract the rudder generated side slip (according to the wool), then the pea would show "slip". In Airbus, the Beta target replaces the streaming wool.

If we have no aerodynamic side slip (streaming wool / Beta) why would we need any aileron?

john_tullamarine

24th Jul 2017, 10:07

With OEI if an aircraft is trimmed for zero side slip it will have some drag due to side loading

Why so ?

The minimum drag position is some slip neutralised by some bank

I can't recall an authoritative source which has minimum drag other than for zero slip.

the pea would show "slip"

I will take the quotes to indicate tongue-in-cheek.

If we have no aerodynamic side slip (streaming wool / Beta) why would we need any aileron?

Beyond my meagre skillset to come up with a convincing two line answer.

However, I refer you to any of the standard references which will take you into headache territory with explanations as to what is going on. You might, for instance, have a read of the USAF FT OEI Good Guts Words (http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA319982).

Vessbot

24th Jul 2017, 13:41

With OEI if an aircraft is trimmed for zero side slip it will have some drag due to side loading

Why so ?

The minimum drag position is some slip neutralised by some bank

I can't recall an authoritative source which has minimum drag other than for zero slip.

You've gotta consider separately the drag on 2 parts of the airplane:

1. The rudder/vertical stab

2. Everything else (fuselage, nacelles, etc)

The drag on "everything else" is lowest at zero slip, obviously.

But the drag on the rudder is lowest when it is centered. And my earlier post explains why it is closer to being centered not at zero slip, but at some amount of slip with the relative wind vector coming from the good engine side.

So the minimum drag for these 2 components is at different slip conditions, and since the total parasite drag is the sum of both of the components, its lowest point will be at some compromise condition between two conditions.

I had actually never thought of this until reading this thread, or if I did, I would have concluded that the difference is miniscule, and trying to compensate for it would have been cutting with a chainsaw what you measured with a micrometer. But it seems that Airbus thinks it's enough to actually matter.

vilas

24th Jul 2017, 17:10

John
The reference you have given in that Chapter 11 page 11.9 Fig.11.10 explains what I was trying to say. It gives case 1 EQUILIBRIUM FLIGHT WITH WINGS LEVEL in which the longitudinal axis of the aircraft is not in line with the relative airflow and that creates drag the side force. Case 2 is EQUILIBRIUM FLIGHT WITH ZERO SIDESLIP in which there is some bank
Case 1: 4 = 0 Figure 11.10 shows the forces and moments for Case 1, the zero bank angle case, with the left engine inoperative. The aircraft is in equilibrium with no accelerations. The pilot would note this with constant heading, ball centered, turn needle centered, rudder opposing the inoperative engine and aileron opposite the rudder to keep the wings level.
Case 2: ß = 0 Another way to balance the sideforce resulting from rudder deflection is by using the W sin if term in the sideforce equation (11.3). Figure 11.11 shows the forces and moments
for the zero sideslip case.
The aircraft is in equilibrium with some bank toward the operating engine, a constant heading and the turn needle centered. The rudder deflection is in the same direction as in the Case 1, however, less 8r is required. The ball in the turn and slip indicator will be deflected in the direction of the bank angle.

And further it states:Three important conclusions can be made from the previous discussion. First, bank angle can reduce the amount of rudder required to achieve equilibrium. Second, an increase in weight reduces the amount of bank required to reduce the sideslip to zero. Third, this configuration will have the least amount of drag. With ß = 0, no sideforce is generated, and therefore no drag due to sideforce is created

Goldenrivett

24th Jul 2017, 17:31

the pea would show "slip"
I will take the quotes to indicate tongue-in-cheek.

vilas
The ball in the turn and slip indicator will be deflected in the direction of the bank angle.

Thanks vilas.

john_tullamarine

25th Jul 2017, 12:58

We're talking at cross purposes, methinks. A quick review of the thread ..

Not trying to be difficult, folks. Just trying to comes to terms with some stuff which appears strange. Caveat, I am not an AB pilot and understand that the automatics do things a little bit differently than, say, manual flight on the Boeings. Lack of AB knowledge specifics might be at play here ...

Post 2 It indicates minimum drag, not zero side-slip.

Conventional wisdom is that min drag occurs at nil slip condition. Nowhere do I see any authoritative reference to bank so I can only presume that the AB comments relate to wings level climb out which is much the same as for the 72/73 where the pilot manually inputs rudder to centre the wheel. This might give a satisfactory result for the Type but I can't see how it equates to min drag which is going to require a bit of bank. Wings level will result in some residual slip - that's fine - but it ought not to equate to min drag.

Post # 3 beta target centered=optimum side slip=min drag

Similar comments to Post #2

Post # 13 Pilot is required to give rudder input to stop the sideslip

Rudder controls yawing moment. Once that is done (wings level and constant heading) there will remain a residual slip angle

Post # 13 Giving rudder input for zero sideslip will require too much rudder deflection

The rudder input is causing the residual slip. If you input more, what happens to heading and slip angle ? Certainly isn't going to give you nil slip.

Post # 17 For minimum drag (no aileron or roll spoiler deflection) at VMCA, then you would need 5 degrees bank

The bank for control considerations is not for performance, rather it reduces slip and frees up a bit of rudder authority. Can you cite any authoritative reference which supports your suggestion that you will have zero slip in the above situation ?

Post # 17 The aircraft will gradually centre the Beta Target resulting a few degrees of bank

This is the only comment I have seen which suggests that the aircraft will climb out with some bank. If that is the case, typically 2-3 degrees or so, then slip will be around nil and drag minimised. Now, what is the case if you are hand flying it rather than switching in the box ?

The FAST reference makes no observation regarding bank.

Post # 25 So the minimum drag for these 2 components is at different slip conditions, and since the total parasite drag is the sum of both of the components, its lowest point will be at some compromise condition between two conditions.

I think not. To get the nil slip condition will require a combination of rudder and aileron input. No value to be had in trying to separate the bits and pieces.

Post # 26 We are agreed. But is there a point to your post other than to restate the paper's words ?

I think what I am trying to get to is whether the aim is to fly with bank or just accept the wings level compromise ?

FE Hoppy

25th Jul 2017, 13:37

On both the EJet and the CSeries. Beta index in the middle puts the ball (trapezoid) and a little bank towards the live engine.

No Idea about AB. It's before my time ;-)

vilas

25th Jul 2017, 14:27

I think what I am trying to get to is whether the aim is to fly with bank or just accept the wings level compromise ?
In case of airbus it is not wings level compromise.
It is fly with some bank. The beta when centred gives you optimum slip and you need some bank to maintain heading and together it makes for minimum drag.

Owain Glyndwr

25th Jul 2017, 15:11

John,

You said you had never seen any authoritative reference to bank. You will find one in Appendix G of Torenbeek's "Synthesis of Subsonic Airplane Design" where he writes:

>It is generally found that the total aysmmetric drag after failure of a starboard engine is minimum for a small negative slip angle, i.e. the airplane slips in the direction of the operative engine. However there is very little drag increment in a flight with zero sideslip. In that condition the most important drag contribution is caused by the vertical tail>
He cites another paper delivered by J G Callaghan of Douglas as part of AGARD Lecture Series 67. (I was there but had forgotten it till checking the reference! - old age)
Callaghan gives a comparative chart showing the various contributions from windmilling, rudder, sideslip, aileron and spoiler. Given the date of the lecture (1974) I think we can safely say it is old technology and a contemporary MDC twin engine design.
Unfortunately his picture has no numerical Y scale, but one can get a good idea of the magnitudes by simple measurement.

For the total aysmmetric drag increment that gives:

Bank/sideslip/drag units
5/-6/5.6
2.5/-2/4.5 (optimum)
1.5/0/4.6 (zero slip)
0.5/2/5.5
0/2.9/6.8 (wings level)
-2.5/6.8/10.9[/B]

You can see from this that the difference between optimum slip and zero slip for this aircraft was pretty damn small! This might not be true for other designs - it all depends on the induced drag factors of the VT and how you use either slip or rudder to generate the corrective yaw. Wings level was definitely off optimum.

Goldenrivett

25th Jul 2017, 17:21

Hi John.
Post # 17 For minimum drag (no aileron or roll spoiler deflection) at VMCA
I would like to withdraw that statement. It was badly constructed.

On Boeings, you can feel the point when no aileron is required. (Hence no roll spoilers deployed)
On Airbus, you can't feel that point. (Hence Beta Target)

See: http://www.dream-air.ru/new/pilotam/a320_instructor_support.pdf
Page 139.
"Hence in order to indicate the amount of rudder required to fly properly with an EO at T/O, the measured SIDE SLIP index is SHIFTED on the PFD by the residual side slip computed value, and displayed in blue instead of yellow, and called BETA TARGET; by pressing the rudder pedal to center the BETA TARGET index, the pilot will fly with the RESIDUAL SLIP as required by the EO condition. Thus theA/C will fly at constant heading with roll surfaces retracted."

Vessbot

25th Jul 2017, 18:02

No value to be had in trying to separate the bits and pieces.

Yes there is. Since the bits and pieces have minimum drag at different states of slip, you cannot understand the total minimum until you understand their contributions separately.

fantom

25th Jul 2017, 19:27

This is getting as silly as it usually does.

If you don't trust beta in an Airbus and you don't believe what JT has to say, then you might as well admit to being a martian.

Escape Path

26th Jul 2017, 01:30

It's an airplane, it should fly more or less the same, Airbus or not.

On engine failures in the sim (A320) I do more or less the same I did on earlier not-so-automated types: Rudder in the correct sense, bit of bank into the live engine, trim the rudder. That's it.

I use B target more to try and help me with the rudder inputs, I bank the airplane anyway. It's worked so far with no particular annotations from instructors.

Re: use of TOGA with low weights and speeds. Vilas said the regulatory performance is met with flex. Airbus FCTM advises to take consideration of the use of TOGA in such cases and that it will "require precise handling". I'd use it but only after initial reactions from the aircraft have been neutralised. However, it seems applying the thrust increase while the aircraft is still on the ground (for the scenario in which you are after V1 but not yet airborne) seems a bit easier to control.

john_tullamarine

26th Jul 2017, 04:37

Thanks folks .. now I'm up to speed on the story.

OG, I was hoping that you might wade in, good sir. Have located your references and they will keep me busy for a while .. I can well see why you might have remembered the AGARD event ... guess I'll have to swot up on supersonic predictions as well ...

Interestingly, I think that the majority of FT folks probably adopt the nil slip idea as min drag. Vessbot, it appears I was a bit behind the intimate bits of the detail .. mea culpa and thanks.

This is getting as silly as it usually does.

Well, yes, and no. The main value of Tech Log to PPRuNe folk is that dummies, such as I, can pick the brains of the SME folk .. and we have a few of those in capital letters. Consider that, for near 50 years, now, I have fondly believed that nil slip was the end of it for min drag. Score one to my education from PPRuNe.

I am being quite serious in this comment. By the ends of our careers, most have acquired sufficient skill etc. to be considered SMEs in this or that. The brighter folk manage half a dozen disciplines. None of us knows it all .. learning continues until the Grim Reaper cuts our run short.

use of TOGA with low weights and speeds. Vilas said the regulatory performance is met with flex.

Of course one can push up to TOGA. But flex will (must) meet all the requirements as that is a necessary prerequisite for the flex setting.

Caveat is that the handling patting-the-head-while-rubbing-the-tummy can get out of hand very quickly. If one is of a mind to increase above flex .. then, please, do it slowly so that the leg can keep pace with the hand and engine response .. that's what the FCTM words "require precise handling" mean. Really, though, unless there is a good reason to do so, why not just leave things as they are and concentrate on flying the thing ? Very much worth the training value to do it for fun, either in the sim or aircraft (the latter at a safe height, etc). If you don't get a feeling that you are hanging onto the tail of the tiger ....

Long while ago now but I was heavily involved with a fatal investigation where they probably would all have survived had the crew left the operating throttle where it was ... pushed it up, yaw, roll, crash, burn, majority died.