Flying Chart Altitudes
Are you a normal human being who gets lost in the sauce when it comes to remembering everything about flying? Do not worry you are not alone. Being a pilot comes with the responsibility to consistently stay in the books and to continue learning. Today we will look at altitudes that you will likely run into while pursuing your flying dreams!
Why chart altitudes? Different altitudes and restrictions are there to keep you and those around you safe. Abiding by them can be the difference between life and death and having an understanding of what each one means will only give you more situational awareness that will come in handy one day.
For this post, we will cover some of the most common chart altitudes. In no particular order, we will define each one.
Minimum IFR Altitude
- On Airways, no lower than any published minimum for the airway
- Off airways fly no lower than the off-route obstacle clearance altitude (OROCA) or the off-route terrain clearance altitude (ORTCA)
- An altitude that provides at least 1,000 ft of clearance above all obstacles within 4 nm of the course to be flown (2,000ft in mountainous)
Minimum Safe Altitude (MSA)
- Altitudes depicted on approach charts which provide at least 1,000ft of obstacle clearance for emergency use within a specified distance from the navigation facility upon which a procedure is predicated
- Consists of minimum sector altitudes and emergency safe altitudes
Minimum Sector Altitude
- Altitudes depicted on approach charts which provide at least 1,000 ft of obstacle clearance within a 25-mile radius of the navigation facility upon which the procedure is predicated
- Sectors depicted on approach charts must be at least 90 degrees in scope
- These altitudes are for emergency use only and do not necessarily assure acceptable navigational signal coverage
Emergency Safe Altitude
- Altitudes depicted on approach charts which provide at least 1,000ft of obstacle clearance in non-mountainous areas and 2,000ft of obstacle clearance in designated mountainous areas within a 100 mile radius of the navigational facility upon which the procedure is predicated and normally used only in military procedures
Minimum Enroute Altitude (MEA)
- The lowest published altitude between radio fixes which assures acceptable navigational signal coverage and meets obstacle clearance requirements (1,000 ft / 2,000 mountainous) between those fixes and applies to the entire width of the airway route or segment to be flown
Minimum Obstruction Clearance Altitude (MOCA)
- The lowest published altitude in effect between radio fixes on VOR airways, off airway routes, or route segment which meets obstacle clearance requirements for the entire route segment
- Only assures acceptable navigation signal coverage only within 25 sm (22 nm) of a VOR
Off-Route Obstruction Clearance Altitude (OROCA)
- Located on IFR en route charts as the sector altitudes between lat/long grids
- An off-route altitude that provides obstruction clearance with a 1,000-foot buffer in non-mountainous terrain areas and a 2,000 ft buffer in designated mountainous areas within the US
- Provides obstacle clearance for any obstacle within the respective grid and 4 nm past the grid lines: “Unlike a MEF, when determining an OROCA the area 4 NM around each quadrant is analyzed for obstructions. Evaluating the area around the quadrant provides the chart using the same lateral clearance an airway provides should the line of intended flight follow a ticked line of latitude or longitude.”
- Check out our article on OROCA here!
Off-Route Terrain Clearance Altitude (ORTCA)
- An off-route altitude which provides terrain clearance with a 3,000 ft
buffer from terrain
- This altitude may not provide signal coverage from ground-based navigational aids, ATC radar, or communications coverage
- Check out our article on ORTCA here!
Minimum Elevation Figure (MEF)
- Located on VFR sectional charts as the sector altitudes between lat/long grids
- Based on the highest point, natural or man-made, within a given grid square
- Determined by adding a 300 ft safety margin plus vertical accuracy factor to the highest point, then rounding up to the next 100
Minimum Vectoring Altitude (MVA)
- The lowest MSA at which an IFR aircraft will be vectored by a radar controller, except as otherwise authorized for radar approaches, departure, and missed approaches
- It may be lower than the published MEA along an airway. It may be used for radar vectoring only upon the controllers’ determination that an adequate radar return is being received from the aircraft being controlled
- Charts depicting MVA’s are normally available only to controllers and not pilots
- Check out more on our article on Minimum Vectoring Altitude here!
Now when you run into some of these abbreviations and specific altitudes you will hopefully have a better understanding of what they are and represent. This is by no means an all-encompassing list, but more of some of the most common altitudes you may or may not see when you decide to do some mission planning for your next flight. With that in mind, having situational awareness from knowing what these terms are will make you and other pilots safer while in the sky!