Is there a rule of thumb for what altitude to fly at? (IFR with the 737NG in particular) I'm aware of the even heading /odd altitude and odd heading / even altitude rule. An example, if I'm flying from say KISP to KBWI, it's only 190 miles. What altitude would you fly at in this case?Thanks.

If i remeber rightly the fmc will give a optimum fl when you enter a cost (i.e 100)i usually choose a couple of thou feet below this....Hope this helps"Lairy"Liam Reynolds

>If i remeber rightly the fmc will give a optimum fl when you>enter a cost (i.e 100)>>i usually choose a couple of thou feet below this....>>Hope this helps>>"Lairy"Liam ReynoldsNot compeletely modelled yet, but if you look at the 800/900 announcement, I think there's info there on the status of cost index and route altitude.The FMS has a rule aside from cost, that the airplane has to be able to achieve a climb, a cruise segment of a certain duration/length (fuzzy on that), and then a descent. It uses that rule to determine max cruise altitude, then applies the cost figure to work out an optimum.I think what you get on the PERF INIT page now on the PMDG is the MAX altitude because the cost modelling isn't done yet.I've looked at some short SWA routes (BWI-ISP, BWI-PVD), and they're typically flown in the mid-twenties (25,26,27,28) when the flight is less than an hour.Hope this helps.

Thanks for the replies guys.

One way to determine a cruise altitude, is after you have entered ORGIN ,DEST,WT and COST index, you will see an entry on the PERF INIT page at LSK 1R- TRIP/CRZ/ALT. The FMC will determine in the trip column the altitude the aircraft can reach and cruise for at least 1 minute. On short flights I will usually select an altitude 3-5k lower than trip altitude and this usually gives at least a 30-50NM crusie on short flights. You can always look at the plan page and see how far apart your T/C and T/D are and then change the altitude on the cruise page to a lower altitude to give you a more approprite crusie segment.