Lord Spandex:
It should really be applicable to anything over MCT though
Which is why I wrote it only applied to MAX TO. Any assumed or reduced thrust may enable TO thrust below MAX TO to be used. It is well beyond the scope of pilots and performance engineers to take all possible combinations of thrust into account so only the MAX TO is assessed. Some cases result in a reduced TO still above MCT, but most are not.
FE Hoppy:
I'd like to know on what basis any OEI procedure has the aircraft not clean and VFTO by the time the 5/10 minutes is up? The only one I can think of is a wrongly calculated take off weight.
Think of a maximum takeoff weight at a high pressure altitude on a hot day, a very high (well above standard) MFRA, with extended turns to enable you to establish on a straight and level segment prior to acceleration. This is the same reason why the 10 minutes if offered to some operators because they NEED it. In EU-area, generally and in terms of performance issues, terrain does not pose many problems, but in other areas of the world this can be more challenging.
FlyingStone:
Given that (at least with Boeing) the swich from 5 minute to 10 min T/O thrust limit is only a paper (and money) exercise, the 5 minute limit shouldn't be understood as hard limitation
The 5 minute should be treated the same as the 10 minute limitation, your AFM does not tell you about the 10 minute allowance, it only tells you about the 5 minute if the engine is classed as such. I agree it does not make a difference as the engine is capable of using it for 10 minutes, but that is another issue. You may only use it when authorised to do so.
If manufacturer has a maximum structural takeoff weight for an aircraft by design but your operator is certified to use one 20 tonnes lower ($$$), would you go over the company imposed limit on that? Think of the same way with the 5 minute, your company has paid for 5 minutes, you do not get 10, although capable of it.
bucks_raj:
Usually all T/o ratings are lower than MCT arent they??
Opposite way around on a jet engine usually, TO trust is usually higher than MCT, hence the limitation.