The area where you fill in ISA DEV in the INIT REF page of the FMC; according to the Tutottial #2 (I think) it is an average for the Cruise Portion of the flight, but isn't it only for the Top of Climb? It says T/C ISA DEV doesn't that mean its the Temp for the top of climb so the plane can better predict VNAV climb or is it for the cruise portion? Doesn't make sense if its for Cruise because it says "T/C ISA DEV."

The area where you fill in ISA DEV in the INIT REF page of the FMC; according to the Tutottial #2 (I think) it is an average for the Cruise Portion of the flight, but isn't it only for the Top of Climb? It says T/C ISA DEV doesn't that mean its the Temp for the top of climb so the plane can better predict VNAV climb or is it for the cruise portion? Doesn't make sense if its for Cruise because it says "T/C ISA DEV."

International standard atmosphere deviation at top of climb. In other words, an average for temperature deviation at the altitude you will be cruising. The tutorial is correct. At the T/C your at your cruise altitude!

Standard atmospheric conditions:Altitude (Ft) Temp (Celsius) 30,000 -44.43 35,000 -55.95 40,000 -56.50Now if your cruising at FL350 and expected temp is showing -58c then you would have a -2c deviation from ISA. Great way to get your average temps along the route is from the Active Sky flight plan feature or various other weather reporting products. If you just adjust your cruise temp on the FMC Perf INIT page it will adjust your ISA DEV accordingly.

The area where you fill in ISA DEV in the INIT REF page of the FMC; according to the Tutottial #2 (I think) it is an average for the Cruise Portion of the flight, but isn't it only for the Top of Climb? It says T/C ISA DEV doesn't that mean its the Temp for the top of climb so the plane can better predict VNAV climb or is it for the cruise portion? Doesn't make sense if its for Cruise because it says "T/C ISA DEV."

Yes, it is used to find the TOC, not for the cruise.Edit: It is used to find the MAX/OPT while on the ground. Not 100% about the T/C, but my book does say it's used to "optimize FMC calculations."So. . . If you're flying a busy sector, and ATC asks during clearance, "Can you accept FL370?" You can check the CRZ page after you've entered the GW and the ISA DEV and have a good idea.

International standard atmosphere deviation at top of climb. In other words, an average for temperature deviation at the altitude you will be cruising. The tutorial is correct. At the T/C your at your cruise altitude!

Ok, thanks but I still dont understand. If I need my ISA DEV at the T/C that could say be +5 or -5C right, but my average Cruise DEV could be alot different over the course of say a 4 or 5 hr flight. So I need to find my average ISA DEV for the ENTIRE cruise portion of the flight and not just the Temp at the Top of Climb.

Ok, thanks but I still dont understand. If I need my ISA DEV at the T/C that could say be +5 or -5C right, but my average Cruise DEV could be alot different over the course of say a 4 or 5 hr flight. So I need to find my average ISA DEV for the ENTIRE cruise portion of the flight and not just the Temp at the Top of Climb.

Enter your ISA DEV for the entire route not TOC.

After U10.7, the FMC uses the SAT above 5000' to find it's cruise performance. Therefore, a route average is useless. If I take off out of ANC for HNL, I don't care what the ISA DEV is at 30N.

After U10.7, the FMC uses the SAT above 5000' to find it's cruise performance. Therefore, a route average is useless. If I take off out of ANC for HNL, I don't care what the ISA DEV is at 30N.

Did some further reading into FCOM and it does indicate to enter TOC ISA DEV for that entry, I stand corrected. Also the wind entry next to it, it is for TOC wind, always thought it was route average.

Did some further reading into FCOM and it does indicate to enter TOC ISA DEV for that entry, I stand corrected. Also the wind entry next to it, it is for TOC wind, always thought it was route average.

SO I WAS RIGHT!!!...that's a first :DWell since we have the latest FMC version I guess it really dones't matter what we put in there right? according to Spin 737.