The assumed temperature thrust reduction is limited to no more than 25% from the selected take-off rating level. This is to ensure that the FIXED derates of CLB1 and CLB2 (10% and 20%) will not be 'voided' by an assumed temp take-off derate being BELOW the armed values for derated Climb.
Hi, CJ.
By "no more than 25% from the selected take-off rating level", do you mean no more than 25% from the normal takeoff thrust(based on the actual OAT).... or no more than 25% from TO, TO1 or TO2?
I notice that when a large value, such as 99, is entered and the maximum allowable SEL temperature value appears(say 69degrees), the "armed" caret next to CLB automatically slides down to the CLB2 setting. This seems to suggest that the FMC is doing its best to avoid a thrust increase at the CLB point. I'm wondering what would happen if I then overrode the CLB2 value with CLB and CLB1... Would the value change?
"In other words, it avoids the thrust being INCREASED when the CLB derate is activated at the thrust reduction point. This is done by automatically reducing the assumed temperature when entered, IF it would have produced that excessive derate."
I don't see the harm in increasing the thrust for CLB (although I am aware that if the derated TO thrust is close to the armed CLB thrust, that the EEC's may not unlock from the TO mode).
[Mutt] Do you mean that the regulatory limit of 25% is for all 747 engines... or for all engines? A colleague thought he saw a greater derate selection on the 777.
Thanks.
Rgds.
Q.