Altitudes

Altitudes you can fly at under IFR.

Cruising Altitudes

Part 91.179.

Unless otherwise assigned (i.e. this is what you normally file), when the magnetic course (that is, overall direction of flight) is between 0° (due North) and 179°, you should file for odd-thousands (e.g. 3,000 ft, 5,000 ft, 7,000 ft). When the magnetic course is between 180° (due South) and 359°, you should file for even-thousands (e.g. 4,000 ft, 6,000 ft, 8,000 ft).

Above FL290, the spacing is different, and depends on whether you are in RVSM airspace (Reduced Vertical Separation Minima):

PARt 91.177.

Except for takeoff, landing, or otherwise authorized by the FAA, you are not allowed to operate an aircraft under IFR below:

• the minimum altitudes prescribed for the flown segment, or:
  • Mountainous areas: 2,000 ft above the highest obstacle within 4 NM of the course to be flown
  • Non-mountainous areas: 1,000 ft above the highest obstacle within 4 NM of the course to be flown.

Definitions

Part 91.177, Pilot/Controller Glossary.

• DA or DH: Decision Altitude / Decision Height. The Altitude (MSL) or Height (above runway threshold) on an instrument approach procedure at which the pilot must decide whether to continue the approach or go missed
• MAA: Maximum Authorized Altitude. Annotated “MAA - 17000” (17,000 ft as an example) on IFR charts.
• MCA: Minimum Crossing Altitude. Minimum altitude you must cross a fix at. Depicted as a flag with an X inside of it on the charts.
• MDA or MDH: Minimum Descent Altitude / Minimum Descent Height. The lowest Altitude (MSL) or Height (above runway threshold) to which descent is authorized on a non-precision approach until the pilot sees the visual references required for landing.
  • You descend to the MDA/MDH, and maintain that altitude/height until you either reach the missed approach point, or you see the visual references required for landing.
• MEA: Minimum Enroute Altitude. The lowest published altitude between radio fixes which assures acceptable navigation signal coverage and meets obstacle clearance requirements. An MEA gap establishes an area of loss in navigational coverage and is annotated “MEA GAP” on IFR charts.
  • The important thing here is adequate navigation signal coverage and meeting obstacle clearance requirements.
• MOCA: Minimum Obstruction Clearance Altitude. Like MEA, but only up to 22 NM from the VOR.
  • If both an MEA and MOCA are specified for a particular route segment, you may fly lower than the MEA down to, but not below the MOCA. You must be able to receive the applicable navigation signals. If you’re using VOR for navigation, this only applies when aircraft is within 22 NM of VOR.
• MRA: Minimum Reception Altitude. Minimum altitude to receive navigation signals.
• MTA: Minimum Turning Altitude. Provides vertical and lateral obstacle clearance in turns over certain fixes. Annotated with the MTA X icon and a note describing the restriction.
• MVA: Minimum Vectoring Altitude: Lowest altitude at which an IFR aircraft will be vectored by a radar controller. Unless otherwise authorized for radar approaches, departures, and missed approaches. MVAs may be lower than the minimum altitudes depicted on aeronautical charts, such as MEAs or MOCAs.
  • MVAs are not published in any aeronautical chart used by pilots. They’re available only to ATC.
• OROCA: Off Route Obstruction Clearance Altitude. Provides obstruction clearance with a 1,000 foot buffer in non-mountainous terrain areas and 2,000 feet in mountainous areas. Does not provide navigation or communication signal coverage.

Last updated: 2021-05-27 19:41:27 -0700