When creating a flight plan, what criteria should I use for determining my cruise level? In particular, for short flights (of about 300 nm or so) is there a minimum time I should be able to remain at the chosen flight level, before it would be regarded as uneconomic to be that high? Is there a formula based on trip length, speed, etc that might serve as a guide? The FMC will calculate an OPT flight level, but I am not sure how it comes by this figure(I think it once suggested FL410 for the above 300 nm trip, which seems a tad high, don't you think?)?Supplementary, quite unrelated question(it just came to mind now :-)): What is the formula for calculating head or tailwind component, please?Many thanks,Frank

Hi Frank,the first rule of thumb for determining CRZ level is to obey to the standard flight level rules (in non-RVSM above FL290, 310-350-390 northwestbound (left quadrant) and FL330-370-410 northeastbound (right quadrant). Then: the higher you go, the better is...depending on many factors...Maybe it's not too economical to climb up to max certified ceiling and start immediately your descent ! Normally airlines try to fly the highest possible level on any flight. But... there are many variables: weather, route availability, local constraints (in Italy, for example, local, that is domestic, flights are not allowed to fly higher than FL290)...Check in the Flight Plan forum and you'll find many thousand of real world FPs, most of them with the filed CRZ level.Regarding the formula for headwind/tailwind: OK, there's a trigonometric formula, but it's quite easier to take a look at the Wind Component Chart at the end of section 5 "performance" of the AFM...Regards.

Frank,Formula for headwind and crosswind componentsα = angle between the aircrafts longitudinal axis (x-axis) and the wind vector measured clockwise.Vw = wind velocityXw = headwind component (If negative, tailwind component)Yw = crosswind component (If negative, component from the left)Xw = Vw * cos α, 0

It's rare that the 737 would go to it's max certified altitude. The FMC is the tool that will give you a general idea of what a good altitude is, and today's fuel prices you better get as high as possible ;D In the real world the pilot has a DISPATCH SHEET that gives him all the flight data to input, of course ATC sometimes does not agree with this but I doubt there are many times one's cruise altitude is effected but could be wrong..Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/southparkcartmad.gif[h3]I WANT MY 747![/h3]Caution! Not a real pilot, but do play one on TV ;-)

Thanks, Enrico.I guess I knew the answer would be complex. :-). Yes, about the flight level rules(which means Cork, Ireland to London Heathrow cannot be FL290, incidentally!). I think I read somewhere that, apart from constraints, you would go to the highest flight level possible that would allow you at least a 1 minute cruise at that level, but I may be misremembering.Thanks for the tip about the Wind Component Chart, which is very useful. I guess the other half of the compass is a mirror image of the one represented?All the best,Frank

Thank you, Mats.Let's see if I can get this formula working:Aircraft heading is 270 degWind is from NW, ie 315 deg @ 35 knotsWind vector measured clockwise is therefore 135 deg(?)So, headwind = 35*cos135 = 35*.99609 = 35K approx! crosswind = 35sin135 = 35*.08837 = 3K approxMaybe I didn't pick such a good example, but I'm wondering if I have the wind angle correct? There is a 45 deg angle between the aircraft heading and the wind direction, but measured clockwise, that is 135(180-45), isn't it?BR,Frank

I remember seeing a show on a flight with a Sterling 737-800 flying from Copenhagen to Oslo and he said that they would climb to the highest level possible which was around FL370 for that day and almost immediately start the descent. So for shorter routes they will actually climb as high as they can before having to descend again.

Thanks, Randy. I realise all of this kind of information is provided to the flight crew. Problem is, we flight simmers have to be our own flight dispatcher, captain, first officer and cabin attendant all rolled into one! :-)BR,Frank

Yes, indeed, Mikkel.On quite a few occasions, I've flown from Cork(south coast of Ireland) to London Heathrow, which is about 300 statute miles. It's mostly all climb and descent, with just a very short segment at cruise level.BR,Frank

Yes, the missing half is a mirror image !The CRZ level for us simmers is a matter of "guessing" and "practice" and "copy of real FPs", since, at least till Mats is done with his flight dispatcher (that seems VERY good !), we are missing a real dispatcher !

Well...If the aircraft heading is 270 and the wind heading is 315, the clockwise angle from the aircraft heading to the wind heading should be 45

Yes, it does, Mats. So, it's when the wind is from the Southwest(225 deg) that the angle will be be 315 deg! Math isn't exactly my strong point, I'm afraid.Thanks,Frank

Yep. You got it! :-)And the value for that crosswind will be negative i.e the crosswind comes from the left. This of course with the aircraft still on a 270

Oh, right!Cheers, Mats.Frank