In general, on a B737 (300/700), we are obliged to use 'rated thrust' whenever:
- Runway is contaminated or slippery
- Marked temperature inversion or windshear
- Antiskid OFF or inop
- Either thrust reverser is inop
- PMC is OFF or inop
- Any power setting instrument is inop
- An RTOW table is not available.
- The aircraft performance calculation requires that we use it ( somewhat obviously )
In all other instances ( including departures when LVP's are in force ) we will use an 'Assumed Temperature Thrust Reduction' technique ( which is not the same as a 'de-rate' ) but only down to the point where the reduction is <= 25% and / or the engine becomes 'flat rated' biased to which ever is the most limiting ( i.e. which ever of these two provides the most thrust ).