Once you start IFR flying you are most probably going to be met with these acronyms. DA, MDA and MSA. So what are they? And how do they relate to us when flying? First of all you will find these three on an approach plate, I will go over each individually and explain how they relate to each other. For the purpose of the explanations below Altitude is above sea level (QNH) and Height is above ground.
DA or DH
DA stands for Decision Altitude and DH stands for Decision Height. DA and DH are found on Precision Approach Plates (ILS). This is the altitude where you will make the decision to execute the missed approach during an ILS instrument approach. The DA has an allowance built into it that allows the plane to descend below it. This is allowed because you only make the decision at this altitude and due to your reaction time, plus the inertia of the plane, you will most probably bust that altitude by a little. See the plate used for this example HERE.
MDA or MDH
MDA stands for Minimum Descent Altitude and MDH stands for Minimum Descent Height . MDA and MDA are found on Non-Precision Approach Plates (VOR, NDB, VOR DME, RNAV). MDA, unlike DA, does not allow you to descend below the altitude (unless you have the runway/lights in sight). This altitude will be the minimum altitude you can descend on the approach, but won’t necessarily be the point where you need to execute the missed approach. The missed approach point is normally a distance from the VOR/NDB. MDA or MDH can be found on a Precision Approach Plate when you look at the minima for the approach with GS out (Glide Slope out/not available). See the plate used for this example HERE.
MSA
MSA stands for Minimum Sector/safe Altitude. This also found on both the Precision and Non-Precision Approach Plates. MSA is the minimum altitude your are allowed to fly within 25 nm of the station (VOR). It gives you 1000ft clearance from terrain according to ICAO standards, however that may differ from country to country. For example South Africa it gives a clearance of 1500ft. It is depicted by a circle separated into “pie slices” with radials, with the minimum altitude allowed in that particular slice. If you are under radar control and identified you may descend below that altitude as long as you still remain above the Radar Altitude specific to where you are. More info on MSA and other related Altitudes can be found HERE.
I hope this brief explanation helps and feel free to ask any questions in the comments below and I will answer as soon as possible.
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