Hello All2 questions1 How do you set the ISA temp and keep the correct ground temp. If I set one the other one changes is this correct?2 What are the settings on the Cost Index? And how do you decide what number goes there?Thank YouJohn G

This really depends on which aircraft... the MD11 is different from the Boeings. Why don't you elaborate and also I recommend posting in the appropriate aircraft section in this forum. Just helps.

ISA is a standard model, why would you want to change it?Cost index is supplied by your company dispatchThe range is 0 - 999 on most types, zero gives you max range speed, for a ballpark figure use anything between 30 and 120 however that is a very simplified answer.I could post some detailed docs on cost index but don't want to be responsible for sending you into a coma..

Sorry about what section I put this. I was talking about B737,8,9. Thank you for the cost index answer. What is the right procedure for putting in the numbers ISA and ground temp or I'm I missing something totally. If I input the ISA temp say -52C the ground temp is totally wrong. Or I'm I totally of base with this. I don't understand this section of the FMC. Also one more thing why does the takeoff info on the speed tape say no v speed if the takeoff speeds are reset.Thanks to all helpJohn G

Sorry about what section I put this. I was talking about B737,8,9. Thank you for the cost index answer. What is the right procedure for putting in the numbers ISA and ground temp or I'm I missing something totally. If I input the ISA temp say -52C the ground temp is totally wrong. Or I'm I totally of base with this. I don't understand this section of the FMC. Also one more thing why does the takeoff info on the speed tape say no v speed if the takeoff speeds are reset.Thanks to all helpJohn G

The PERF INIT ISA number is the deviation from standard ISA, so if standard ISA temp at sea level is 15 C and the probe says 10 C the ISO dev is -5 C.Re takeoff speeds, you move the computed speeds to the right hand column in the TAKEOFF REF page. Then the speeds will appear on the tape. if you then change any runway, weights, etc., the speeds are erased and have to be re-applied.Hope that is what you are asking.r

Thank you RonYou've answered my questions.ThanksJohn