VFR Altitudes

Alex E

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Jun 28, 2008
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After reading 7-8-5 of the .65 it says altitude assignment for VFR aircraft (class C airspace) should be assigned altitudes that meet MSA OR MVA OR MIA. Is it the lower or higher of the 3? All ensure obstruction clearance.

In the case of a prescribed MIA or MVA, the altitude is easy to determine with the use of charts. However, VFR aircraft departing to a general direction of flight will probably not be on an ATS route which has the prescribed altitudes, therefore we will be using the MSA or the MIA (2000 feet above highest obstacle in mountainous area, 1000 in non-mountainous)...how does ATC assign VFR altitudes that are hard to determine? Are we able to utilize the MEF's and add 1000/500 feet? Or even better, use MVA's?

I believe a pilot can accept a decent below the MSA. (I.E a decent to join the glideslope)...where in the FARs does it say an aircraft can operate below the MSA?I think a pilot must have the field in sight, although I'm not sure. Thanks.
 

Roddy_Piper

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Jun 15, 2008
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I believe a pilot can accept a decent below the MSA. (I.E a decent to join the glideslope)...where in the FARs does it say an aircraft can operate below the MSA?I think a pilot must have the field in sight, although I'm not sure. Thanks.
A pilot can descend below the MSA/MIA/MVA to join the localizer/glideslope when he is on a segment of an approach. You can't just arbitrarily descend an aircraft below MSA/MIA/MVA because you figure he's gotta get low enough to land anyway. You get him established on a segment of the approach and let him descend via the approach below the MSA/MIA/MVA. Issue a restriction to cross the IAF or IF at a safe altitude first, then let the pilot descend.

That's my take. Not sure if your question was really about that or something else more specific.
 

Centerpuke

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Sep 22, 2008
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I am reasonably certain that MSA's are not assigned. That is a pilot only altitude that ensures obstruction clearance and does not pertain to ATC. In other words, it is the altitude the pilot derives from his/her sectional. MIA's are designed for off-route segments. i.e. if a pilot is not on an airway, it would be the lowest assignable altitude, it is the MSA for controllers. On the airway, it would be an MEA that that is used which ensures signal coverage and obstruction clearance. MVA's do NOT peratin to a VFR aircraft. MVA's are the lowest altitudes that an IFR aircraft can be vectored. So, to try to answer your question, if the aircraft departs and is not on an airway, it must be issued an altitude above the MIA. If the aircraft is VFR and is on an approach, I would assume it is a practice approach. Once you agree to give the practice approach, the aircraft is then treated as if it were IFR. At this point, the MVA must be used. It is also a precarious situation because VFR's are not normally given hard altitudes. They are expected to maintain VFR. Deviations high and low can be expected and seldom declined. That is the ARTCC take on it.

Maybe this helped a little?
 

Roddy_Piper

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On the airway, it would be an MEA that that is used which ensures signal coverage and obstruction clearance.
Excellent response. Your spot on.

Just a quick add on though. Center MIA charts are not the real MIA. An MIA is 1000 AGL in non-mountainous areas and 2000 AGL in mountainous areas within 4 miles laterally. Center MIA charts are a very rough safe estimate of the real MIA. For example, you may have a few high mountains in a certain area that derives the MIA box on the center chart that sits above the sector. In reality if a pilot really wanted to use his sectional he could be below the center derived MIA and be 100% legal. This is because there would be an insane amount of MIA boxes and become pretty cumbersome when you pull up your MIA map on your radar.