Which factors need to be considered when deciding on Flight Levels? I can imagine that Company SOP's and aircraft type play some part? Let's say a B737-600 with a Flight Plan from EGLL to LHBP; what would be a bog standard FL? I have to say that when I construct a FP I just pick a FL 'off the cuff' - as long as it seems reasonable :) but I never feel really comfortable doing it that way.Ken

IFR is @ 1000FT intervals, VFR is @ 1000 + 500FT intervals (so 1500, 2500 ect). As well headings of 0 - 179 are odd numbers (1000, 3000 ect) and headings of 180 - 359 are even numbered (plus 500 feet if your flying VFR so).This is a fantastic webpage for some flight rules in MSFS>>>>http://www.navfltsm.addr.com/index.htmXP Home SP2Asus P4P800-SE Intel 3.0GHZDDR 400 D/C 4x512MBLeadtek 6800GT 256MB (77.72)SB AudigyCH Products Yoke/Pedals USBSee you in the fence...CYYZ

Hi altstiff,Many thanks for your reply. I followed up your link as well; as I expected there's more to it than thinking of a number :) . Ken

Hi,There is a rule of thumb (more or less) for shorter routes (< 250nm)The distance is your FL.For longer routes your FL depends on :- Max certified altitude - Weight (Step climb)- Winds at different altitudes- Available FL's (due to other traffic)Ceteris Paribus (everything else equal) you opt for the highest possible altitude, i.e. max certified altitude for that particular aircraft.Most of the time it's the most economical.

>IFR is @ 1000FT intervals, VFR is @ 1000 + 500FT intervals>(so 1500, 2500 ect). As well headings of 0 - 179 are odd>numbers (1000, 3000 ect) and headings of 180 - 359 are even>numbered (plus 500 feet if your flying VFR so).>That is misleading.In the UK it is not mandatory for VFR flights to cruise at any particular altitude but it is recommended that they adopt the IFR cruising level system which is:At flight levels below 24,500 ft 000 - 089M: Odd thousands of feet089 - 179M: Odd thousands of feet plus 500 ft180 - 269M: Even thousands of feet270 - 359M: Even thousands of feet plus 500 feetAt flight levels above 24,500 ftLess than 180M: 25,000, 27,000,....41,000 or higher levels at intervals of 4000 ft180 but less than 360M: 26,000, 28,800,.... 43,000 or higher levels at intervals of 4000 ftSource: CAP393 Air Navigation: The Order and Regulations - Section 2 Rules of the Air Regulations Clause 30

Well in Outer Slybodia they have no flight rules. Even dogs and chimps are permitted to fly. More so the ones that can smoke cigars. In Outer Slybodia anyone can do as they wish when it comes to flight rules (kind of like flying on "the zone").Point taken.For the record we are talking about MSFS, not real world flying.....Do you get mine?XP Home SP2Asus P4P800-SE Intel 3.0GHZDDR 400 D/C 4x512MBLeadtek 6800GT 256MB (77.72)SB AudigyCH Products Yoke/Pedals USBSee you in the fence...CYYZ

In Jets the optimum FL is based upon various considerations.Some are,flight distance,en route winds,cost index which is basically how much fuel vs speed you want,turbulence forcast and aircraft performance which will be based off total weight.Most of those are plugged into the FMC to determine an optimum FL which may then be altered based on wx etc.Then you pick the nearest suitable level which conforms with the hemispherical rule and away you go.Darren

I see you have the PMDG 737.Within the general rules, the FMC will indicate the optimum flight level for your route taking into account the weight of the aircraft.You need to enter all your route & flight data into the FMC before this comes upOn longer flights, it will tell you when to increase your height for optimum fuel use as the weight comes down.You can request flight level changes from FS ATC

I was just making the point that many areas of the world do not use US rules. Indeed, there have been cases in Europe of US business jet passengers being off-loaded and told to return by scheduled flights because ramp checks showed the aircraft didn't comply with EU/local requirements.I've refrained from making the obvious reply to your response.

Short answer:Distance of the flight.Comfort level of passangers, CAT, weather avoidance etc. Costs, higher the level the lower the costsSpeed and direction of the jet streamISAATC traffic.That's all I can think of for now.Regards,Ed

Excellent answers so far. The ideal FL will be based on aircraft weight; the heavier the lower is the optimum FL. Therefore you could choose to pick a cruising FL mid way between your Top of Climb weight (fat with fuel) and your Top of Descent weight (much lower on fuel).

Hi ailchim,Thanks for your reply, I'm using the PMDG B737NG-800; when setting up the FMC a required input is the Flight Level (I forget, at the moment, which page of the FMC). So I thought I'd 'fill in the gaps' in my knowledge of how to choose a Flight Level. But I can now leave it to the FMC.I thank everyone else also for their replies; I'vt taken a copy of this thread and can now digest it all, at my leisure :) Everyone has been most helpful.KenSomerset, England

The actual flight level though is assigned by ATC based where possible on the requested optimal altitude mentioned in the filed flightplan.If a route is rather busy at that FL, ATC is free to assign a different (almost always lower) altitude instead to avoid congestion, or change the flightplan to route through a less busy portion of airspace.

One reason why turboprops are back in fashion again. They tend to occupy the realtively free airspace below the jets and so can be operated in optimum conditions.

I have to say I've hardly flown the 737 since I got the Level D 767 and I'm basing my comments on what the 767 does plus my recollection of the 737 but, hey, who wants a re-run of that debate over 2 excellent products! You are right, the FMC does require the entry of a FL, but if you guess that initially (surprisingly low for a heavy medium/long-haul 767 (FL320 to start?) and surprisingly high for a light short-haul 737 (FL360 or even FL380)), the FMC will come up with a recommendation and you can alter you own input to suit. This doesn't seem to cause any problems - but then I use FS ATC so adding altitude restrictions during the climb phase in the FMC is counter-productive, you get the aircraft trying to do one thing and ATC insisting on another. If you had all your intermediate altitudes plumbed into the FMC, not quite sure what a last minute change in cruise altitude would do. Presumably not a lot until you got close to TOC.The FS flightplan is another thing altogether. I use FSNavigator to generate these, so I complete the FMC input to set the initial flight level, and only then load a saved FS flightplan, whereupon I can edit the cruise altitude to suit.One thing to note. Be careful about West/Even, East/Odd.If either you set this incorrectly for your own aircraft or your AI traffic is wrong, you'll find AI traffic coming the other way hurtling at you at 900mph at the same altitude! TCAS tends to get in a bit of a panic about that!You can use AI Traffic Mover http://www.molitor-home.de/FS/AITM/ to ensure your AI flight plans are at appropriate altitudes and much else besides!