B737 OAT input error with correct ATM
An incorrect OAT temperature input to the FMC resulted in an insufficient N1 generated by the FMC. The incorrect OAT input was -52C instead of 16C. However, the correct Assumed Temperature of 50C was entered into the FMC as well. How is it then, that the FMC produced an N1 that was grossly insufficient for the take off? I cant seem to find the relationship between the OAT and the Assumed Temperature and N1. I mean, if you input -52C instead of 16C the initial N1 will be quite low since the air is denser. But then you are Assuming to 50C. As the temperature increases the N1 will increase to the Flat rated temp (around 30C) then the N1 will start decreasing again until you get your Assumed Temperature N1. So the question is, how can entering a wrong OAT make such a huge difference on the N1 considering you entered the correct Assumed Temperature in the box?