Dear Forum,

Why did LNM stop suggesting a cruise altitude for my flight plan? 

Am I missing something? I know I can choose one but I havent got a clue how high to go! 

Please help.

Thanks

Edited February 27, 20215 yr by nasaspaceboy

I'm not sure of what you are flying, but in general, higher is better for fuel efficiency. That fact is also balanced by the distance in your flight plan. Time/distance to climb and descend will also be a factor in how high you will cruise.  

5 hours ago, nasaspaceboy said:

Am I missing something? I know I can choose one but I havent got a clue how high to go! 

 

This clue wasn't based on anything 🙂

Now it's better solved - you can use aircraft's performance profile (choose aircraft you want to fly) + flight planning tool (for example you can choose only high Jet airways).
For short hauls you should open Flight Plan Elevation Profile (button) and change flight level/altitude as long as  cruise time is enough for you.
Sometimes flight is so short that it's impossible to climb and descent than .... level. After that  you can automatically adjust (button) level according hemisphere rules.
IFRs are rounded to nearest 1000`, VFRs are rounded to nearest 500` according rules are set in options. In LNM options you can change these Hemisphere rules to  - East/West, Norht/South or South/North. In general Est/West is used but some countries use other rules during flying via airways described in Enroute sections of AIPs (New Zeland, France, Italy, Portugal, Spain).
There is also one very strange country - Chile - East/West rule is used but axis is not along 360/180deg but is 30/210deg (because of country size and location) - it's described in their regulations.
What's very nice implemented at this moment LNM shows you warning (in red color) when your flight level is outside of minimum/maximum flight level for a given airway's segment.

In real aviation many factors are taken during calculations - optimum cruising altitude can change as weight is changing (fuel burn), especially during long or ultralong (>12hrs) hauls - it's so called step climbing. Also optimum cruise altitude and climb/descent profiles usually are calculated in reference to special parameter so called "cost index" (if you fly airliner you know where to find this in FMC) - it's a kind of balance between fuel price and other prices (the most important are pilots' and staff prices).
In short: 
-cost index = 0 -> only fuel price counts, so flight is calculated for maximum saving fuel;
-cost index = MAXvalue (in most airliners it's a 100 but sometimes it can be 500 or other value -> aircraft's manual) -> fuel price is unimportant you have to get into the destination as quick as possible.
Other values are a balance between fuel and non-fuel costs. Every airline has got their own cost index factor for different planes and different flights - you can dig on Internet there are some tables with such values. If you use well implemented airliner and would like to fly with real cost index factor taken into calculations - you should load your flight plan (created in LNM) into FMC and type in required cost index -> then FMC should display calculated flight level or altitude (depends where you fly - in northern/polar Canada there are area where transition altitude is 24000ft - it's not a joke) - that you can retype this again in LNM and adjust level according hemisphere rules.

Remember - LNM can calculate fuel  because it can collect burning fuel info directly from simulator and then use this for future forecasting.
But sometimes the add-ons report wrong values to LNM and this calculation is bad.So if you've got special add-ons - use dedicated stuff for them.

On the other hand - if you don't care about "realism"  choose the simplest strategy - as  @G550flyer wrote "the higher the better", IMHO it's the best advice in this subject! ;D

Regards,
Piotr

Edited February 27, 20215 yr by ppgas