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Dear fellas I'm building a program to simulate flight plans, for academic purposes and, I have read a lot about flight levels and specifications but I need to be absolutely sure of what I am doing.

The reading that I have made always mentions the circular rule: Eastbound – Magnetic track 000 to 179° – odd thousands (FL 250, 270, etc.) Westbound – Magnetic track 180 to 359° – even thousands (FL 260, 280, etc.) I couldn't find any examples when flying in the opposite direction (179° to 000 ) neither any mention to flight level change when crossing from from westbound to eastbound (359° to 45) , reason for which I'm quite confused.

I got the data regarding the airports (lat, long) from https://openflights.org/data.html

They mention that for Longitude: Negative is West, positive is East, e.g. CDG (Paris) 2.549, FRA (Frankfurt) 8.570, LIS (Lisbon) -9.135

So my questions are:

1) if I am flying from LIS to FRA is it a westboung flight fom LIS until longitude 0, and then it becomes an eastbound flight from longitude 0 to FRA?

2) based on the previous question, the flight plan should consider taking off from LIS climb until to an even flight level e.g. FL380, cruise at FL380 until the aircraft reaches longitude 0 and change the cruise flight level to an odd flight level eg FL390?

I would really appreciate your help (I am not a pilot, I'm doing a PhD in Operations Research)

Francis

Francisco Lemos
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    LIS is west of FRA, therefore generally the flight is eastbound. – Cpt Reynolds May 06 '19 at 18:29
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    East and West does not flip at longitude 0.... – Ron Beyer May 06 '19 at 18:33
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    As you said the rule is based on the magnetic track of the flight, how is that related to crossing longitude 0? – fooot May 06 '19 at 18:34
  • So part of your question is what happens if the plane is actually flying westbound but the magnetic track is between 000 and 179 degrees? Find a student pilot to sit down w/ you and get you straightened out, it will be good for you both. – quiet flyer May 06 '19 at 19:19
  • The special case is actually flying in the polar region where magnetic compasses become useless. Look up grid navigation. – user71659 May 06 '19 at 20:07

3 Answers3

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Your mistake is in thinking that geographic Longitude 0 and the longitude + and - values east or west of Longitude 0 are a factor in all this.

It's a lot simpler than that. It's even FLs on any track west of north/south on any longitude anywhere, and vice versa. In other words, even heading for the sunset, odd heading for the sunrise, anywhere on earth.

So Lisbon to Frankfurt being a north easterly direction, it's odd, and you would file an odd FL in your Flight Plan.

It's a convention. What happens in practice though is that the FL you're assigned is often a couple of levels above or below, and while it usually sticks to the convention, it may not always, especially if close to a N/S track or the track will flip through north or south and change from westerly to easterly as a result, because it curves around for some reason, or some other expediency, and a controller my clear you to an odd FL even though you are technically going westbound, or vice versa. But anyway...

Another complication: the track requirements usually change from magnetic to true when in the higher latitudes, depending on the local airspace designations, generally north of 60 to 70 deg.

John K
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"Westbound" does not mean "currently located on westerly line of longitude". It means "going westward". The track of the flight as drawn on the earth's surface is progressing toward the west.

quiet flyer
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A plane flying direct from LIS (LPPT) to FRA (EDDF) will follow a magnetic track of 045. Since 045 is between 000 and 179, it is "eastbound" and should therefore use an odd flight level. It's really that simple.

The convention of west longitude and south latitude being negative is just to allow storing coordinates in computer databases as two signed numbers, i.e. without separate direction flags. It has nothing to do with the above rule, which predates computers.

StephenS
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