Thrust Setting selection...?

[gerard]

Hi,

I’ve got a question for those who can answer in regard to the Take-Off and Go-around selection thrust settings.

On the Airbus A340 I believe that these are similar (if not equal). If this is the case, why have two different settings?

Secondly, are there any potential problems if an aircraft inadvertently selects Take-Off instead of Go-Around?

Thanks.

[Mad (Flt) Scientist]

NB This is not an A340 answer, just a more general thought.

Since TO thrust applies to the TO configs and GA thrust to the Landing and GA configs, you might (however unlikely) be in a situation where a high TO thrust can be tolerated from VMCA considerations (without excessive perf penalties) but be unable or unwilling to use a high VMCL associated with using that thrust as GA thrust. So maybe you would tailor each thrust to be the best balance between high thrust giving intrinsically better performance, and high thrust causing high VMC which then causes poorer performance.

I doubt anyone goes into that level of thought over it, though.

[Soiled Glove]

I believe that there are 2 throttle detents that can be used for take-off on the A340 and I am sure it is available on other aircraft in addition - certainly the Airbus fleet. The Take Off Go Around (TOGA) setting is used to provide the maximum thrust that the engines are capable of and would be generally used for a go-around situation where the priority is to apply max thrust and get the aircraft climbing at max rate. The second detent is often referred to the Flex setting where the aircraft (engines) have sufficient performance to allow take off at a reduced power setting thereby reducing noise, fuel consumption but most importantly increasing engine life - if required the engines could be increased to TOGA during a flex take-off if for example windshear was encountered and the pilot required more thrust. The flex setting is programmed into the FADEC etc and means that the engines are 'limited' to a lower 'false' datum. On more powerful aircraft at a light take-off weight, there could be as much as 25% reduction in thrust on each engine - this would obviously lower Vmca etc. The flex setting is calculated such that should an engine fail then before V1 the aircraft has sufficient runway to stop, or if above V1 then the take-off could be continued with the engines remaining at the flex setting, though TOGA could be used on the remaining engines if necessary. The concept is similar to the military aircraft where a dry power take-off can be performed on a clean F-16 etc but a loaded up F-16 would use Reheat.