SkyWestCRJPilot
Now a CAL FO
- Joined
- Aug 20, 2002
- Posts
- 359
If you operate in predicted mode on the FMS and input all of the appropriate variables the FMS will tell you whether or not you can fly at that altitude. You have to input your present weight, the desired altitude, the ISA deviation (not at your current altitude but your requested altitude from your winds aloft information), and your desired mach. If the FMS says you can't do it then it will say at the bottom something like "unable altitude". You can even input the altitude in divisions of 100s of feet to find out exactly how close you'll be. For example you type in 39,000 and it says unable. You type in 37,000 and message disappears. You can type in 37,400, then 37,500, etc. till it again says unable so you can see exactly at what altitude the FMS says you can't fly at. In my experience it was very accurate and always more conservative than the table in the flip cards. The key is that you have to be in predicted mode and input all of the corresponding variables, and especially the ISA deviation, and what it will be at your requested altitude not where you are now. You may be at FL330 and think FL370 will work out but you start your climb and you climb through the tropopause. Instead of it being ISA -5 it's now ISA +10. Uh oh. Check your winds aloft temps and compare with an ISA graph to see if you can do it. Predicted mode provides lots of good information that measured mode won't ever give you. Just make sure you input all of the pertinent information in.