When setting up for tutorial 1 the following comes from the tutorial regarding derating. My question is since it is 8c in Denver right now and if I were flying is 8c what I would enter in LSK1 "SEL/OAT. In other words alway enter the departure tempurature.

Type 40 into the scratchpad and line select it into LSK 1L to enter

an additional assumed temperature of 40C on top of the fixed

derate.

Assumed temperature is a more complicated concept than the fixed

derate, but the basic idea is as follows:

The engines are designed to produce their rated thrust at an actual

outside air temperature of 30C (ISA + 15C). If the temperature is

higher than this, the air becomes less dense and the engine

produces less thrust at the same N1 setting. When we enter an

assumed temperature that is higher than the actual outside air

temperature, we’re telling the engine computers to act as if that the

air is less dense than it really is and it will reduce the N1 limit to

produce somewhere around level of thrust that it would if the

temperature was actually the higher value.Thanks

You enter the assumed temperature for de-rate as per performance tables or perf calc program.If you do not use assumed temperature, you do not need to input anything.

Thanks, I can only assume that real world, lightly loaded AC would always derate in colder weather to save fuel.

On the contrary, derated take-offs are in fact less fuel efficient. However they save a lot of engine wear thereby reducing maintenance costs.

One should never discount the added safety achieved when a derated TO results in an appropriately timed ground roll. This allows for the "Stable, TOGA, HOLD, 80kts, V1, ROTATE, V2" sequence to arrive at expected intervals, and allows proper monitoring of TO performance and timely reaction to abnormals. A lightly loaded airplane without derates is often akin to holding on to a tiger by the tail- slightly unnerving at best.

Edited January 31, 201214 yr by lasnubes

A lightly loaded airplane without derates is often akin to holding on to a tiger by the tail- slightly unnerving at best.

Yes, but it's a lot of fun! :(