MDA

[Guest markyp]

Hi all,I know DA and DH one uses Radio Alt the other uses Baro,However when you have set one of these can you also dial in somehow the MDA?? If so how??When do you use MDA or when DA??ThanksMark

[Guest tmetzinger]

MDA are used for non-precision approaches (LOC, BC, VOR, NDB, RNAV).MDA is the lowest altitude you can go until you can make normal maneuvers visually to land.The difference between DA and MDA is that DA is with an ILS and you're flying a glideslope and you're only at DA for an instant, and and reaching DA defines your missed approach point - you decide whether to proceed or miss the approach.In a non precision approach, your vertical path isn't specified, beyond the fact that you cannot descend below MDA. Your missed approach point is defined as a point in space, usually crossing the VOR, a distance from a VOR, an intersection, or even a time from the Final Approach Fix. Often the missed approach point is at the airport itself or the runway threshold. So you don't want to be reaching the MDA at the same time you reach the missed approach point, because at that point you may be right over the runway and won't be able to make a normal approach to it.So, a "normal" non precision approach has you reaching MDA at a point in space where you could see the runway environmant and land. This could be as far out as several miles.You will normally set your MDA as your BARO minimumss, and this will serve as a reminder that you cannot descend further until you have adequate visual references to make a normal approach and landing.You can descend to MDA using LVL CHG, VS, or VNAV, but one "catch" with using VNAV is you need to define a point far enough away from the airport that you can see the runway, and use THAT point as your MDA waypoint.It's early in the morning, so I don't think this is as clear as I'd like, I'll watch for follow-on questions.Best wishes,

[Guest markyp]

Hi Tim,No I think that has helped!! Feel free to elaborate a tad more if you want to!!ThanksMark