AMA vs MEF

[aholenstein]

Does anyone know what the difference is between Area Minimum Altitude on the Low Chart and Maximum Elevation Figure on the VNC? I know the AMA provides a minimum 1000ft obstacle clearance and MEF 328ft.

But if you look at the images below (Ottawa Area) the is several thousand feet difference between the AMA and MEF. Anyone know why?

Thank you!

Screenshot_20231221_204222_FltPlan Go.jpg (1.49 MiB) Viewed 1278 times

Screenshot_20231221_204209_FltPlan Go.jpg (677.38 KiB) Viewed 1278 times

[linecrew]

AMA shows minimum obstacle or terrain clearance of 1000 feet (2000 feet in mountainous areas) and the MEF shows the lowest possible VFR flight in a quadrant (about 500 feet above obstacles or terrain)

[Conflicting Traffic]

Does anyone know what the difference is between Area Minimum Altitude on the Low Chart and Maximum Elevation Figure on the VNC? I know the AMA provides a minimum 1000ft obstacle clearance and MEF 328ft.

But if you look at the images below (Ottawa Area) the is several thousand feet difference between the AMA and MEF. Anyone know why?

Thank you!

I'm not sure why there's a discrepancy there. It's possible the areas covered don't match. The quadrangles are not defined by regulation, and the chart maker has the discretion to use larger (or smaller) areas. I can't tell from the screenshots if that's the case here.

Your clearance for the MEF is zero feet for human-made obstructions and 328 feet (100 meters) for natural obstructions, both rounded up to the next 100 feet. I don't know why there's a distinction made here between natural and human-made, but I *think* it's because natural obstructions include trees, which can grow.

[digits_]

AMA shows minimum obstacle or terrain clearance of 1000 feet (2000 feet in mountainous areas) and the MEF shows the lowest possible VFR flight in a quadrant (about 500 feet above obstacles or terrain)

The difference is over 6000 ft though. Do they use different quadrant dimensions on the IFR charts?

[oldncold]

Many restricted sites in the yow area ie 3000agl parliment. Etc. You will see this as terrain elevation changes out west too. Where you on the same lo chart ,will be required to fly higher alt. (Stepup. Segment) .Or will not be cleared by atc due to obstructions .

[Fly0nTheWall]

AMA shows minimum obstacle or terrain clearance of 1000 feet (2000 feet in mountainous areas) and the MEF shows the lowest possible VFR flight in a quadrant (about 500 feet above obstacles or terrain)

The difference is over 6000 ft though. Do they use different quadrant dimensions on the IFR charts?

VNCs are Lambert Conformal Conic Projection. And I believe LOs are Transverse Mercator? Also the scales are different (much more area covered on a Lo). So, the quadrants by default would be different dimensions.