Flying Altitude

Hello guys,

There seems to be a lot of confusion here so, if you don't mind, I'll try to clear it up.

There are two kinds of vertical separation these days: CVSM (Conventional Vertical Separation Minima) and RVSM (Reduced Vertical Separation Minima) and in both case, the semi-circular rule applies:

When following a 000-to-179° track, an aircraft should fly at an odd level or altitude.

When following a 180-to-359° track, an aircraft should fly at an even level or altitude.

In CVSM airspace, the minimum vertical separation is 1.000 ft below FL290 and 2.000 ft above.

This difference comes from the fact that this separation rule is quite old now: When it was implemented, only a few jet aircraft (B-707, DC-8, Comet) were in service and able to fly above FL290. Navigation and altitude instruments were not very reliable at that time, therefore the double vertical separation above FL290.

In RVSM airspace, the minimum vertical separation is 1.000 ft. RVSM airspace is from FL290 up to FL410 only. Below and above it, we still have CVSM: Consider this as a sandwich made of two slices of bread (CVSM) with a slice of RVSM in between. (Sorry guys, I couldn't help this comparison!).

So what brought RVSM? Why suddenly, somebody decided to reduce the vertical separation? Only two reasons prevailed: Airspace congestion bringing huge delays (costing airlines a lot of money) and future traffic increase.

Lateral separation could not be reduced safely because most of en-route control centers are using multi-radar systems which, technically speaking do not allow a less-than-5 Nm lateral separation.

On another hand, aircraft's navigation and altitude instruments were becoming more reliable and accurate with very minimal errors. So, RVSM has been implemented above FL290 to allow more traffic to go through and reduce congestion.

RVSM was first implemented over the Atlantic Ocean and a couple of years ago in Europe. About a month ago, it was implemented as well in 11 more countries (Middle East, Pakistan, India) between Turkey and the western borders of Asia.

I have been working with RVSM for about a month now and have to say that it's great: Not only pilots are getting more easily their preferred level (the ones calculated by the FMS) but potential conflicts are fewer too as we have 6 additional levels to accommodate the same amount of traffic.

Before going, a last reminder of the levels used, depending on the type of vertical separation used:

CVSM

Eastbound (odd levels): FL270, 290, 330, 370, 410... Westbound (even levels): FL280, 310, 350, 390, 430...

RVSM

Eastbound (odd levels): FL290, 310, 350, 370, 390, 410. Westbound (even levels): FL300, 320, 340, 360, 380, 400.

My apology for being so long but I thought this topic deserved some explanation.