Semi Circular Rule:

The semicircular rule (also known as the hemispheric rule) applies, in slightly different version, in all of the world, including in the Angolan controlled airspace.
The standard rule defines an East/West track split:

  • Eastbound – Magnetic Track 000 to 179° – odd thousands (FL 250, 270, etc.)
  • Westbound – Magnetic Track 180 to 359° – even thousands (FL 260, 280, etc.)

At FL 290 and above, if Reduced Vertical Separation Minima are not in use, 4,000 ft intervals are used to separate same-direction aircraft (instead of 2,000 ft intervals below FL 290), and only odd flight levels are assigned, depending on the direction of flight:

  • Eastbound – Magnetic Track 000 to 179° – odd flight levels (FL 290, 330, 370, etc.)
  • Westbound – Magnetic Track 180 to 359° – odd flight levels (FL 310, 350, 390, etc.)