Choosing Altitudes
DRVSM - Domestic Reduced Vertical Separation Minima

Overview 

The objective of the DRVSM program is to implement RVSM between flight level FL290 - FL410 (inclusive) in the airspace of the lower 48 States of the United States, Alaska, Gulf of Mexico and Atlantic High Offshore Airspace (including Houston and Miami Oceanic airspace) and the San Juan FIR.

The implementation date/time was January 20, 2005 at 0901 UTC. On the same date and time and at the same flight levels, Canada and Mexico implemented RVSM. Canada implemented RVSM in its Northern Domestic Airspace in April 2002 and expanded it into Canadian Southern Domestic Airspace in January 2005.

Prior to the implementation date, aircraft flying between FL290 and FL410 were required to maintain 2,000 ft. vertical separation. The RVSM program enabled vertical separation to be reduced between FL290 and FL410 (inclusive) from 2,000 ft. to 1,000 ft. RVSM was first implemented in North Atlantic Airspace in 1997. It is now implemented in other major airspaces such as Europe, the Pacific Ocean and Australia.

Choosing Altitudes 

Altitudes for direction of flight at and below FL410 are determined using the "east is odd, west is even" rule. Aircraft heading from 0 degrees (360 degrees) to 179 degrees inclusive should be at an odd cardinal altitude. Aircraft aircraft heading from 180 degrees to 359 degrees should be at an even cardinal altitude. VFR aircraft should be at a cardinal altitude appropriate for their heading plus 500 ft. VFR is not permitted at or above FL180. Aircraft travelling above FL410 are assigned an odd cardinal altitude that alternates between westbound and eastbound headings. See the chart at the end of this document.

What Cruise Altitude Should Be Filed in a Flight Plan?

For IFR flights, most of the time there will be little question about this.  An altitude should be chosen that is appropriate for the predominant direction of flight, and that should be filed as the cruise altitude.  The direction of flight while executing departure procedures during climb-out should not be considered. 

Occasionally, a flight will start out heading in one direction, and then eventually turn to the other.  In this case, the filed cruise altitude should be appropriate for the first cruise segment of the flight.  For example, a flight from KDAB to KMYR along the route OMN->CRG->SAV->CHS will be predominantly westbound on the KDAB->CRG segment of the flight.  On the CRG->KMYR segment, the direction will be predominantly eastbound.  The flight plan should include a filed cruise altitude appropriate for westbound flight.  At CRG, ATC has the responsibility to ensure that the current altitude of the aircraft is appropriate for the new direction, or is responsible for ensuring separation of aircraft, if left at the filed cruise altitude.

For VFR flights, the filed cruise altitude should be appropriate for the direction of the first segment of flight (not including climb-out).  This should be a cardinal altitude plus 500 ft.  Under visual flight rules, it is the pilot's responsibility to ensure that he is cruising at an altitude appropriate for his current direction of travel at all times. If taking advantage of VFR flight following services, the pilot may announce his intentions to climb or descend to a new altitude to the air traffic controller.  The air traffic controller cannot assign a specific altitude to VFR flights operating outside of Class B airspace, but can provide updated traffic information, weather and altimeter.  The air traffic controller will provide the necessary information, remind the pilot to maintain VFR, and will suggest whether the altitude change is advised based on current traffic conditions.   The air traffic controller may not know what cruise altitude was filed for VFR aircraft, because the flight strip might have been updated to show "VFR" as the current cruise altitude.  This helps the air traffic controller identify VFR flight-following aircraft separately from IFR aircraft.

Altitude Selection Chart

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