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# Decision Height

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Could anyone tell me how to work out the decision height or MDA from the charts from the UK AIP?Here's an example: http://www.nats-uk.ead-it.com/aip/current/...EGKK_8-1_en.pdfIt gives the different categories but not for DH..instead it gives the OCA - I don't even know what this means....Also..once I have the DH or MDA, do I use the radio or barometric knob to set it in the 747?Thanks,Robert T

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The 747 is catagory D so you need to look under that section. CATI is 378ft on the Baro or 182ft Radio altCATII is 280ft on the Baro or 84ft Radio alt (Autoland)MDA is 3000 I use the Navigraph charts so if I'm wrong the guy's here will correct me. Also never heard of OCA but a quick search say's it's CEILING-VISIBILITY?? Rob

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From the first item I found in a google search:The Decision Height DH or Minimum Descent Height MDH isn't on the charts because it is a calculated value for different conditions and different airfields.For a precision approach, the DH is definedFor a non-precision approach, the MDH is defined.The definitions differ according to the pilot's qualifications.For a precision approach, the minimum height to which a pilot must descend before executing a missed approach is referred to as the Decision Height. (For a non-precision approach, it is referred to as Minimum Descent Height). The DH depends on a number of factors. Using Hawarden Runway 23 ILS Approach Plate for example: -a) Obstacle clearance height (OCH) for a category A aircraft with a 3% climb grade performance capability is 300 feet above aerodrome level (QFE).B) Add the aerodrome threshold elevation (from the approach plate) (17 feet) to obtain the OCH above sea level of 317 feet (QNH).c) The minimum descent height for an ILS approach is 200 feet aal. Check which of a) or B) is the greater. In this case it is a).d) Is an altimeter correction necessary? For a precision approach, an altimeter correction of +50 feet is required.e) IMC rated pilots must add 200 feet to the minimum descent height thus far calculated. The minimum is therefore increased to 550 feet aal.f) The absolute minimum descent height for an IMC rated pilot on an ILS approach is 500 feet aal. Check if d) is greater than 500.g) In this case it is, so the Decision Height (DH) is 550 feet, and the Decision Altitude (DA) is 567 feet.See also: http://www.jeppesen.com/download/misc/Volu...Ch10_Page18.pdf

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Great find Dan! I always thought the MDA was the lowest altitude you could descend to until established on the G/S or visual due to terrain??Rob

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Great find Dan! I always thought the MDA was the lowest altitude you could descend to until established on the G/S or visual due to terrain??Rob
What you describe sounds like MSA (Min Safe Altitude), which is shown on approach plates within a circle and sometimes different quadrants will have different MSA. Once established on GS you then descend to DH.There are so many intricate details to an approach. A good reference is the FAA Instr Pilot Handbook: http://www.faa.gov/library/manuals/aviatio...lying_handbook/

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MDA - Minimum Descend Altitude is used for non-precision approaches only. It is the minimum altitude you can descend to in the approach. Once reached you can fly level up to the Missed Approach Point (MAPt) or Go-Around (as some airline ops subscribe).DA(H) - The altitude (or height) on a precision approach at which the decision musdt be made to land or go around.Xanderp.s. The MSA is the minimum altitude which can be flown that gaurantees 1000' terrain clearance in a a circle of 25 NM's around the reference point (written below circle). What rjprest describes can indeed be the MSA and/or the initial approach altitude. But the MSA is indeed the bare minimum when there is no RADAR service.

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Thanks very much for the information Dan. You've managed to clear up a lot of things for me. You are right in saying that the approach is very intricate - as it is the place where I usually mess up the whole flight...Robert T

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The 747 is catagory D so you need to look under that section. CATI is 378ft on the Baro or 182ft Radio altCATII is 280ft on the Baro or 84ft Radio alt (Autoland)MDA is 3000 I use the Navigraph charts so if I'm wrong the guy's here will correct me. Also never heard of OCA but a quick search say's it's CEILING-VISIBILITY?? Rob
Just wanna clarify.....the 747 is only a catagory D if it

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