Performance increase from FLEX to TOGA Takeoff in an Airbus

[CokeZero]

Hi

Been trying to figure out the performance increase when going from a Flex to TOGA takeoff. I know variables such as temp, pressure, weight etc all play a part in the calculation. Reading literature from the manual does give a little bit more information but if at the start of the takeoff roll you decide to use TOGA instead of say Flex 40, what increase could I expect in terms of distance or a percentage increase in thrust?

I hope this makes sense.

[Goldenrivett]

Hi CokeZero,
If TOGA thrust is flat rated to +28 degs C (301 degs Kelvin), then FLEX probably reduces the engine thrust by approximately 10% for every 30 degs C above 28 degs C.

So if you planned to set flex to 40 (12 above + 28) but then set TOGA, then you should get an extra 12/301% thrust (i.e. about 4%).

If you needed say 80% thrust Single Engine just to fly level without accelerating, then every 1% increase in thrust (above 80%) increases your performance by approximately 5%.

[vilas]

With improved FADEC standards MAX flex thrust reduction upto 40% is permitted and is used by many airlines.

[sierra_mike]

as flex can not reduce thrust more than 25% of max

max thrust reduction used to be 25%, amended fairly recently to 40% by CS-25 amendment 13. but as vilas said, you need to have certified equipment to do so.

[CokeZero]

thanks everyone

I knew it wasn't a simply solution but does give me food for thought when predictions don't work out as planned.... cheers

[Denti]

Been trying to figure out the performance increase when going from a Flex to TOGA takeoff. I know variables such as temp, pressure, weight etc all play a part in the calculation.

Wouldn't the biggest variable in this question be the flex temperature used vs the OAT? There should be quite a difference increasing from flex 35 to TOGA on a 45°C day vs. increasing from flex 70 to TOGA on a -15°C day.

[sierra_mike]

agree Denti, the bigger the difference between FLEX Temp and OAT the more you benefit from TAS effect.
but FLEX Temp must never be lower than OAT

...from flex 35 to TOGA on a 45°C day...

[Denti]

True that, i should probably refrain from posting under the influence....

[TSIO540]

The V speeds for a FLEX thrust takeoff are also valid at TOGA (FCOM-PER-TOF IIRC).

If you increase thrust to TOGA you will accelerate faster and reach V1 in a shorter distance (all other factors being equal).

Originally Posted by CokeZero

Hi

Been trying to figure out the performance increase when going from a Flex to TOGA takeoff. I know variables such as temp, pressure, weight etc all play a part in the calculation. Reading literature from the manual does give a little bit more information but if at the start of the takeoff roll you decide to use TOGA instead of say Flex 40, what increase could I expect in terms of distance or a percentage increase in thrust?

I hope this makes sense.

[divinehover]

It all depends. If the OAT is 28 deg and you FLEX to 29 deg, the perf increase will be minimal. In a A340-600 you can FLEX to 74 deg. In that case if the OAT is 0 deg, the perf increase will be large (as explained above)