Use of TOGA with Flex speeds
 

Interested to know your thoughts on the following:

Regarding take-off performance.

The scenario is, you are on stand and plan for a Flex take-off. Whilst taxying out, due to bad weather in the vicinity of the airfield, Captain suggests the use of TOGA instead. You do not however re-calculate the performance based on TOGA, instead you keep the speeds from the Flex calculation.

My question is, is this safe?

A couple of things which I would like to clarify:

a) with the use of TOGA, normally the performance calculation would give a reduced V1, so your decision point on the runway would be earlier. The Flex V1 would be higher/later.

b) in relation to point a) - say our Flex V1 was 140 kts. With TOGA, you would reach this speed at an earlier point on the runway, allowing a slightly longer remaining stopping distance, therefore is the use of TOGA with Flex speeds considered more conservative?

Thank you for any replies in advance.

Of course it's safe!

You said it yourself. You'll reach the originally calculated V1-speed earlier down the rwy, so if you abort at V1 you'll be able to stop earlier down the rwy as well.

Also, your climb performance will be better.

I don't understand what makes you having doubts about using the speeds calculated for the flex TO with TOGA thrust.

Regards,
Erasmus

Not always I'm afraid...

If your performance calculations for your flex take-off have a very low V1, then sometimes, that V1 is lower than Vmcg for Full thrust T/O. This depends on how your performance is calculated, and can be an issue if your airline uses min V1 as standard for flex. take-offs or when RWY WET.
Therefore, you should never use a V1 that is lower than Vmcg full thrust just in case of your said scenario or a panick reaction by PF at V1...
Remember that V1 is calculated for your reduced temperature thrust input, Vr and V2 are calculated for actual aircraft mass.

The same in case of windshear during the t.o. run the concept of V1 is lost.
Or when you forget to set Flex Temp. and TOGA is applied but with Flex calculated speed.

Maybe safe but WRONG,why the rush?:confused:

One thing I have to consider on my aircraft (777), if changing thrust setting on the roll is to recheck the stab trim setting, as the nose-up pitching moment with the thrust increase wiill require a different setting....apart from VMCG considerations at lower weights..the increased thrust will give you guaranteed performance..... Zlin.

Our company's laptops always calculate the speeds with Vmcg for max thrust as a minimum V1 speed.

Starting up those laptops, inserting the new data, do the calculation and insert them into the FMGS will take 3 or 4 minutes at least. Sometimes you have the time and sometimes you don't. I will not delay my TO (and delay traffic taxiing behind me) just to do unnecessary TO speed recalculation. Now if you're talking about delaying the TO due to the weather, of course that can be considered if it looks unsafe to take off.

Laptop guys....you dont have qrh speeds in your fmc?Or a handy fcom?
Walking on thin ice i say...

DE-FACTO,

The speeds that may be generated by some FMS systems or from the QRH are not optimized and are not taking into account things like runway slope, obstacles etc.

To get the RTOW charts out (if you have them, if you have LPC laptop you won't) would take just as long as starting up the laptop and cross checking the numbers.

Airbus specifically warns that the speeds must not be mixed and matched, so best to take a moment and update the FMGS with the updated information.

I can't speak for other types but from the A320 series FCOM

"Using the same takeoff chart, for a given weight it is possible to :
‐ Select a temperature lower than the maximum determined one and keep the speeds defined at maximum temperature"

If you decide to reduce below TREF use TOGA.

Wake up at the back!

Surely VMCG only refers to Full T/O thrust? On a flex takeoff it is always safe to apply TOGA if necessary. e.g. windshear, engine failure.....

But if you DERATE the T/O thrust VMCG will decrease.....

TP

Agree on having to look at the rtow charts as well however If you aint climb or runway limited in the first place (as they used ass temp),they wouldnt be limited using full thrust...obstacles and slope are the same..

Not flying Airbus but that IS exactly my point.

It the same as ohhh the runway is now wet..let s just cut 10kts off V1..:rolleyes:

As has been pointed out, V1 for flex or Assumed Temp is always available, and calculations always take into account VMCA/G for TOGA thrust.

HOWEVER- A Fixed-Derate (TO1 or 2 on some Boeings) only takes into account Max thrust at the derated setting, so using fiew-wall TOGA may exceed the allowable thrust re VMCA/G

Not needed Zlin- the 777 has a speed trim, so the setting is the same regardless of thrust.

de facto, that's absolutely not what we're talking about here.

The question is: "You have calculated a reduced thrust setting with the corresponding V-speeds. Is it now "safe" to use the same speeds with a higher thrust setting (TOGA), all other factors (rwy conditions, weight...) remaining the same?"

The simple answer is yes! If Airbus talks about not mixing and matching speeds, they're not talking about setting TOGA. Setting TOGA at any point during the TO roll is always an option. (On the A320 anyway. I would be amazed if it were different on any other jet)

Don't worry, if it suddenly starts raining and the rwy gets wet, the laptop will come out and new TO settings will be checked. (If it was likely to start raining, we would probably have had those numbers available already :ok: )

Sounds like music to my ears:ok:

I suggest you guys read

"Getting to grips with Aircraft Performance" before you start fooling around with TOGA Derates and Flex speeds. :ok:

Specifically look at the nice color graph on page 49.

http://www.smartcockpit.com/data/pdf...erformance.pdf

@nitpicker330

I fail to see what your graph offers in this discussion.

The question here is about increasing thrust from Flex to TOGA. So lets look at the effects:

V1's relationship with VMCG hasn't changed as VMCG was based on TOGA.
VR and V2 were based on weight which hasn't changed and VMCA which also hasn't changed.

The only thing that has changed is the acceleration rate of the aircraft. We now reach all of the speeds earlier.

In the case of engine failure before V1 we stop the same mass from the same speed (energy) but starting at an earlier point on the runway and therefore stopping earlier.

In the case of and engine failure above V1, again this would be at an earlier point than in the FLEX case (failure at the same speed) and therefore we reach screen height earlier and subsequently our gross and net climb are above those we would have had with flex.


As many have already pointed out. The gotcha is not from flex to TOGA (RATED) but from De-rated to TOGA. In this case VMC may change and therefore the V speeds need to be checked that they are still above the minimums for the new thrust.

The bigger problem I see is the mixing of balanced and un-balanced calculations by grabbing speeds from other sources.

I looked at the graph and I fail to see how it would be relevant to this discussion.
(I didn't have to download the book. I've had it since I started flying the A320. The book was mainly written by an ex-colleague from SABENA:D who joined Airbus after the bankruptcy. :{)

Want to do some other reading? Then read this: Understanding Takeoff Speeds by Airbus.

The note on page 6 says:
"Flexible Thrust is a thrust reduction, designed to save engine life. This thrust is reduced
to take advantage of the available runway length, when full thrust is not necessary
(from a performance perspective), but takeoff speeds with full thrust still apply."

Now, are you guys still not convinced that there's nothing wrong with using TOGA with the "FLEX-speeds"?

Well ok but.....

1/ we are not Test Pilots
2/ keep it simple
3/ follow your company SOP's with regards to selecting TOGA during De-Rated thrust T/O's etc
4/ if you make up your own rules and get away with it then lucky you, if you don't then expect a lot of sh** to come raining down on you from high up :ok:

5/ if that means delaying T/O for 4 mins while you re do the numbers then so be it........

Remember that if you start operating outside the normal green band SOP's then mistakes can and do happen. You do so at you own peril no matter how simple it may seem at the time.

Basically if you stuff up your Balls are theirs.....:sad:

Thanks for the link to that Airbus doc. I think I've read it before but now I've downloaded it. :ok:

Just ran the numbers in our RTOW computer for the same weight, field conditions Flap setting etc with the only change being Flex v TOGA.

Flex gave a V1 of 19 kts faster
Flex gave a Vr of 15 kts faster
Flex gave a V2 of 13 kts faster

So flying at TOGA thrust but retaining Flex speeds is conservative and thanks to the document mentioned above seems to be ok with AB.

However that being said unless I had a very good reason to get airborne ASAP I would take a moment and re do the numbers. :ok:

@nitpicker330

You're welcome! :ok:

I was just about to post a link to Wikipedia's definition of "nitpicking" :E

Best regards,
Sabenaboy

I said in my first post that using toga with atm speeds may be safe but wrong...wrong as the speeds dont correspond to the thrust ..call me pedantic.
Id rather use the most correct speeds for the thrust used...if you reject at your higher v1 speed (atm) with full thrust and blow a tire,you will then have to explain why your v1speed at which you rejected was higher...in that case you should have continued,,,,,hence the parallel with the v1 speed correction for wet runways.
I cover my a@@@ then i think about traffic behind..
Performance wise we agree.

Hi de facto,

If you insist on changing your V speeds just because you've decided to use TOGA rather than Flex, please can you do both of those calculations at the gate before you move, so I don't have to wait behind you.

Again it takes a few secs to do so,,,,fmc beauty..now you wont have time to get close enough...
Wet speeds are calculated in advance.:hmm:
At age 63,,,believe me youll still be at the gate while ill be lining up for takeoff:E

The original question is (as I understand it) .. "Is it safe to increase takeoff thrust to TOGA from Flex?".

Given the lack of other information, I'll make some assumptions.

• We are talking Airbus.
• Flex for one Airbus type is the same as Flex for another.

The Flex thrust rating on Airbus is effectively an assumed temperature reduced thrust from TOGA - ie Flex with no assumed temperature is the same as TOGA. Given this, the min control speeds that are used in the Flex calculation are the TOGA speeds.

• So, is it safe? Yes. You will have reduced field length requirements, will reach your V speeds faster and have improved climb gradients.
• Would you get a better result recalculating? Yes. You will get V speeds more appropriate to your situation.

So we have two considerations ... Is it Safe ... Is there a better way ...


For what it is worth.


N

Thank you for the input guys.

Like nitpicker330, I also ran a couple of calculations through the LPC yesterday.

These are the results I got. It should be noted, these results are based on a TORA of 3500m, sea-level, and an airfield without any high obstacles or terrain, ISA temperature and a QNH of 1004. I am mentioning this, incase it is of significance in analysing the results.

The Flex calculation gave the following speeds:

Flex 57
V1: 152
V2: 152
VR: 154

(min V1 - 152, min V2 - 120, Vmcg - 113)

TOGA gave the following speeds:

V1: 141
V2: 142
VR: 145

(min V1 - 120, min V2 - 120, Vmcg - 113)

Whilst I understand the logic of reaching the Flex V1 speed sooner on the runway with TOGA thrust, hence greater remaining stopping distance, I would like to ask about the decision to stop or go. It would seem you could end up in a situation, with TOGA thrust but Flex speeds, where you stop above what would be the normal V1 for that thrust setting. Any comments on this?

Secondly, I do not understand why the minimum V1 is so high for the Flex calculation.

Thank you once again for your insight.

Read my post!For your second question, your V1 is higher but your stopping distance from point of reject will be same as no atm because actual outside air is what counts.(TAS really).
You obviously in that case have a very long runway and light weight.

Hi
By Flexing, you have matched your performance to the runway length available so effectively end up with a Balanced Field Length where the Min V1 (continue) & Max V1 (stop) are coincidental.

When using TOGA you have more performance, so even at the min V1 (continue) you will be able to accelerate within the runway length available to VR. With TOGA on the long runway you now have a range of V1s and usually the software chooses the middle one.

de facto, sorry mate, I missed your post pointing out the same earlier.

It would therefore seem, the practice is wrong in that case.

Any other opinions appreciated.

rudderrudderrat, thank you for the clear and concise explanation. :ok:

I think so but yet some prefer to hurry up and leave it to statistics...i dont.

As I said earlier, we are not TEST PILOTS.

If you company has a SOP in place to allow you to select TOGA at the last minute and not FLEX then fine........

If not then be prepared to justify your decision in a subsequent court of law should something go wrong. Don't expect your Chief Pilot to defend you either.

So, if there is any doubt there is no doubt.

Take the extra 3 minutes, I'll wait if I'm behind you :ok:

Rudderrat:

Flexing does not give you a balanced field. You can have an optimized calculation with an assumed temp. Wizo nailed it. Read his post again.

Using TOGA obviously makes your flight safer, performance wise, even if you don't recalculate speeds.

Airlines want us to use reduced thrust to save on engines so if we are so concerned about using TOGA and not changing the speeds, aren't we saying using reduced takeoff thrust is dangerous and we should always use max? It seems like a lot of pilots are saying that in this thread.

If you want the lowest V1 then just use the max takeoff flap setting and max power. I'm sure the airlines would love that.

I think we are nitpicking this to death, personally.

Yep, I am not sure what test pilot territory is entered here.

Whow, so now I deserve the title "test pilot" because I dare to set TOGA with the original flex speeds? Thanks, I'm honoured :O. I can tell you this "procedure" (I wouldn't even call it that) has been "tested" regularly at Sabena and my current employer and many other operators without doubt.
Nitpicker330 added that sentence to his post, after I had posted my reply #22. After reading his last contributions, I think it's now time to put that link up anyway.

Here's what Wikipedia says about nitpicking: "As nitpicking inherently requires fastidious, meticulous attention to detail, the term has become appropriated to describe the practice of meticulously searching for minor, even trivial errors in detail (often referred to as "nits" as well), and then criticising them"

I suppose that nitpicking shouldn't be used for these replies because that implies that there were indeed trivial errors to be be found. There aren't!! This thread should have ended after my first reply.
Let me turn it around, nitpicker, de facto and others: show me one SOP or give me one good reason why setting TOGA with the original flex speeds would be unsafe! Please refrain from posting if you can't.

If you're in front of me, I would sure hope you'd have the courtesy not to delay my departure while you're doing unnecessary speed recalculations :sad:. If the only delay you're creating is your own, then be my guest and nitpick all you want in your cockpit.

Hey sabena man,

Did i ever write in my posts that it was unsafe?no!for the second part ill deal with the delay to have speeds matching the thrust setting used.
Personal choice thats all.

Small country big ego i see..:E

https://lh3.googleusercontent.com/-i...640/V1.001.jpg

If you look at this little picture and consider the original Flex V1 to be at the point the two lines cross, then increasing to TOGA is the same as moving downwards into the "Whatever" zone.

When You flex you reduce the thrust to match the space available. As you reduce the thrust the range of V1 that would allow a safe outcome reduces. If you can reduce all the way until you become runway limited then you are at the point where the lines cross and you only have one V1 available. But that V1 is always within the usable range for higher thrust settings.

Vr and V2 are essentially based on weight (stall speed) and the only reason you might get different values with different types of calculation (rated / flex) is down to the engineering selection of Vr/V2/Vs ratio. For our flex calculation with added thrust the original Vr and V2 are still valid.

DESPEGUE

You are confusing De-rate with Flex. Flex IS a full thrust take-off, only full thrust is assumed at a higher temperature. All performance is calculated for the higher temperature, therefore actual performance will be better than predicted.

Derate is a different story entirely. in the cast of Derate, Vmcg is definately a limiting factor as the thrust is calculated - amongst other things - rudder efficiency, with its limit governing the amount asymmetric thrust it can control.


One advantage of FLEX, is that TOGA can be selected at any time throughout the take-off and first few segments of climb. Derate on the other hand, has limits and conditions (i.e.: speeds must be greater than "XXX" whilst in CONF 2 or 3, etc, etc).

With FLEX Thrust Management, TOGA is a lot like Viagra. You can Fuc& without it, but using it makes you feel better with the only side-effect being that your bitc& screams a little louder.