When flying anywhere you need to climb, cruise, and then descend. But you must comply with the rules and fly at certain predetermined altitudes.
The Rules: Neodd and Sweven
When you are flying above 3000 feet AGL you must fly at an even-numbered thousand feet if you are traveling west. That is what sweven means. If you are traveling directly South, or on any Westerly heading then fly on the even-numbered thousands.
Conversely, if you are traveling East or directly North, fly at an odd thousand (neodd).
For IFR flights to the East you will fly at 5000 or 7000 or 9000 feet, etc….
For VFR flights you must be 500 feet above these altitudes. So a VFR flight to the West would cruise at 4500 or 6500 or 8500 feet, etc….
These rules are for cruising altitude, meaning that if you are flying up above 3000 to practice an emergency descent then you can just climb to whatever altitude you want.
Why is this rule in place?
This rule is a bit of a compromise between safety and simplicity.
When two planes approach head-on their closure speed, the speed at which they are approaching each other, is very high. Even a relatively slow 152 will approach another 152 at around 180 knots TAS if they are head-on. For faster planes like an arrow traveling at 150 knots the closure speed is 300 knots!
It is safer to fly at these altitudes because VFR planes flying East will always be 1000 feet vertically separated from VFR planes flying West. Furthermore, they will be separated by 500 feet from all IFR traffic.
This is great, but there is a problem! What if planes approach nearly head-on but both traveling East? One of them could be traveling 010 degrees (which is East of North) and the other could be flying at 170 (which is East of South).
This is where the compromise comes in. The rule could split the compass into 4 segments but then it would be more complicated and difficult to remember.
Always stay vigilant looking for traffic that might be climbing/descending, not following the rules, or might be at a near head-on angle.
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