[{"data":1,"prerenderedAt":426},["ShallowReactive",2],{"learn-\u002Flearn\u002Fdecision-altitude-and-mda":3,"learn-nav-\u002Flearn\u002Fdecision-altitude-and-mda":383},{"id":4,"title":5,"body":6,"date":314,"dateModified":315,"description":316,"draft":317,"extension":318,"faqs":319,"howTo":315,"keyTakeaways":329,"meta":335,"metaDescription":336,"navigation":337,"path":338,"quiz":339,"seo":365,"series":366,"seriesOrder":367,"sources":368,"stem":380,"topic":381,"__hash__":382},"learn\u002Flearn\u002Fdecision-altitude-and-mda.md","Decision altitude and minimum descent altitude",{"type":7,"value":8,"toc":300},"minimark",[9,13,19,24,32,49,60,63,67,88,92,106,110,113,149,152,156,163,167,174,193,197,208,219,223,237,252,256,288,292],[10,11,12],"p",{},"Every instrument approach ends at a number: the lowest you may go before you must either see the runway or go around. But that number comes in two flavours that behave in opposite ways, and confusing them is one of the more dangerous mistakes on an approach. One is a gate you pass through; the other is a floor you must not break.",[14,15,16],"blockquote",{},[10,17,18],{},"This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.",[20,21,23],"h2",{"id":22},"two-minima-for-two-kinds-of-approach","Two minima for two kinds of approach",[10,25,26,27,31],{},"The minimum you fly to depends on whether the approach gives you ",[28,29,30],"strong",{},"vertical guidance",".",[10,33,34,35,40,41,44,45,48],{},"A ",[36,37,39],"a",{"href":38},"\u002Flearn\u002Fthe-ils-explained","precision approach"," or an approach with vertical guidance brings you down a glidepath to a ",[28,42,43],{},"decision altitude (DA)",". Because you are descending continuously on a glidepath, you cannot stop in mid-air at the DA; you arrive at it and ",[28,46,47],{},"decide",", in that instant, to land or to go around.",[10,50,34,51,55,56,59],{},[36,52,54],{"href":53},"\u002Flearn\u002Fnon-precision-approaches","non-precision approach",", with no glidepath, brings you to a ",[28,57,58],{},"minimum descent altitude (MDA)",". Because you manage the descent yourself, you can, and traditionally did, level off at the MDA and fly along it, looking for the runway.",[10,61,62],{},"That structural difference, a continuous glidepath versus a managed descent, is why the two minima are defined and used so differently. It is not pedantry; it changes what you are allowed to do with the number.",[20,64,66],{"id":65},"decision-altitude-a-gate","Decision altitude: a gate",[10,68,34,69,72,73,79,80,83,84,87],{},[28,70,71],{},"decision altitude"," is the height on the glidepath at which a missed approach must be initiated if the required visual reference has not been established. The key feature, set out in ",[36,74,78],{"href":75,"rel":76},"https:\u002F\u002Fstore.icao.int\u002Fen\u002Fprocedures-for-air-navigation-services-pans-aircraft-operations-volume-i-flight-procedures-doc-8168",[77],"nofollow","ICAO Doc 8168",", is that the aircraft is ",[28,81,82],{},"expected to descend slightly below the DA"," as the go-around is begun, because an aeroplane cannot reverse a descent instantly. That small dip is ",[28,85,86],{},"built into the obstacle clearance"," for the procedure, so it is safe and anticipated. You decide at the DA; you do not have to have stopped descending by the DA.",[20,89,91],{"id":90},"minimum-descent-altitude-a-floor","Minimum descent altitude: a floor",[10,93,34,94,97,98,101,102,105],{},[28,95,96],{},"minimum descent altitude"," is the altitude ",[28,99,100],{},"below which you must not descend"," unless you have the required visual reference to continue to a landing. There is no built-in allowance for dipping below it, so the discipline is different: you must arrive at the MDA and ",[28,103,104],{},"not go below it"," until you either see the runway and can land, or reach the missed approach point and go around. Where the DA tolerates a momentary descent below, the MDA does not. Busting an MDA, descending below it without the runway in sight, is exactly the error the floor exists to prevent.",[20,107,109],{"id":108},"da-dh-mda-and-mdh-the-datums","DA, DH, MDA and MDH: the datums",[10,111,112],{},"Two pairs of terms describe the same points against different datums, and the difference matters for the lower categories.",[114,115,116,132],"ul",{},[117,118,34,119,121,122,124,125,128,129,31],"li",{},[28,120,43],{}," and a ",[28,123,58],{}," are read on the ",[28,126,127],{},"barometric altimeter",", referenced to ",[28,130,131],{},"mean sea level",[117,133,34,134,121,137,140,141,144,145,148],{},[28,135,136],{},"decision height (DH)",[28,138,139],{},"minimum descent height (MDH)"," are referenced to ",[28,142,143],{},"height above the ground or the threshold",", and the DH for CAT II and CAT III is read on the ",[28,146,147],{},"radio altimeter",", because at those very low minima the aircraft needs to know its height above the surface precisely, not just its altitude above the sea.",[10,150,151],{},"So an ILS CAT I uses a DA or DH; a CAT II or III uses a radio-altimeter DH; and a non-precision approach uses an MDA or MDH. The letters tell you both the kind of minimum (decision versus floor) and the datum it is measured against.",[20,153,155],{"id":154},"the-required-visual-reference","The required visual reference",[10,157,158,159,162],{},"Neither minimum lets you continue on faith. To descend below a DA, or below an MDA, you must have the ",[28,160,161],{},"required visual reference"," in sight and be in a position to make a normal landing. The rules list what counts, the approach lighting, the runway threshold and its markings or lights, the touchdown zone, the runway identification, and require enough of it to continue safely. If, at the DA or by the missed approach point, you do not have the required references, the decision is made for you: go around. The minimum and the visual reference work as a pair; reaching the height is not permission to land unless you can also see what the rule demands.",[20,164,166],{"id":165},"where-the-numbers-come-from-and-the-cdfa-twist","Where the numbers come from, and the CDFA twist",[10,168,169,170,173],{},"The published minima are not arbitrary. They are built up from the ",[28,171,172],{},"obstacle clearance altitude or height (OCA\u002FOCH)",", the lowest altitude that guarantees obstacle clearance for the procedure, with margins added for the aircraft category and the operation. That is why the same runway can show different minima for different approaches and different aircraft.",[10,175,176,177,181,182,188,189,192],{},"There is one practical wrinkle when a non-precision approach is flown as a ",[36,178,180],{"href":179},"\u002Flearn\u002Fstabilised-approaches-and-cdfa","continuous descent final approach (CDFA)",". Because a ",[36,183,187],{"href":184,"className":185},"\u002Flearn\u002Fglossary#gt-cdfa",[186],"glossary-link","CDFA"," flies a continuous descent and goes around at the minimum rather than levelling off, operators often add a margin to the MDA to create a ",[28,190,191],{},"derived decision altitude\u002Fheight",", so that the go-around, with its small dip, does not actually bust the MDA. It is a neat reconciliation: the MDA stays a floor, but you fly to a slightly higher derived figure as if it were a decision gate.",[20,194,196],{"id":195},"why-the-difference-exists-obstacle-protection","Why the difference exists: obstacle protection",[10,198,199,200,203,204,207],{},"The gate-versus-floor distinction is not an accounting quirk; it comes straight from how the ",[28,201,202],{},"obstacle protection"," is built. On a precision or vertically-guided approach, the procedure designer knows the aircraft will be on a defined glidepath and can model the ",[28,205,206],{},"go-around exactly",", including the brief descent below the DA as the aircraft transitions from descent to climb. That dip is inside the protected surface, so it is safe by design, which is precisely why you are allowed to reach the DA still descending and decide there.",[10,209,210,211,214,215,218],{},"On a non-precision approach there is no glidepath to anchor that model, so the protection is built around a ",[28,212,213],{},"level minimum"," with no assumption that the aircraft will sink below it. The MDA is therefore drawn as a hard floor: descend below it without the runway in sight and you are outside the surface that was protected for you. The same logic explains the ",[28,216,217],{},"missed-approach"," design. From a DA or the MAPt, the published missed approach assumes a climb at a defined gradient along a protected path, and the minima and the go-around are designed together. Understanding that the numbers come from protected surfaces, not from habit, is what makes the rule about the dip, allowed at a DA, never assumed at an MDA, click into place.",[20,220,222],{"id":221},"a-worked-example","A worked example",[10,224,225,226,229,230,233,234,236],{},"You fly an ",[28,227,228],{},"ILS"," down the glidepath to a ",[28,231,232],{},"decision altitude of 550 ft",". At 550 ft you look up and ",[28,235,47],{},". You have the approach lights and the runway in sight and are positioned to land, so you continue, and it is entirely normal that the aircraft passed a few feet below 550 ft in the instant you committed. The DA was a gate, and you went through it with the required visual reference.",[10,238,239,240,243,244,247,248,251],{},"Now fly the same runway as a ",[28,241,242],{},"VOR approach"," to a ",[28,245,246],{},"minimum descent altitude of 820 ft",". This time you descend to 820 ft and ",[28,249,250],{},"level off",", because the MDA is a floor. You fly along at 820 ft toward the missed approach point, looking for the runway. If it appears and you can land, you leave the MDA and descend visually; if you reach the missed approach point still at 820 ft with nothing in sight, you go around, never having dropped below the floor. Same runway, two minima, two completely different rules about what the number permits.",[20,253,255],{"id":254},"common-pitfalls","Common pitfalls",[114,257,258,264,270,276,282],{},[117,259,260,263],{},[28,261,262],{},"Treating an MDA like a DA."," You may dip below a DA during the go-around; you must not descend below an MDA at all without the runway in sight.",[117,265,266,269],{},[28,267,268],{},"Continuing below the minimum without the required reference."," Reaching the height is not enough; you need the specified visual references and a position to land.",[117,271,272,275],{},[28,273,274],{},"Confusing DA and DH datums."," A DA is altitude above the sea on the baro altimeter; a DH for CAT II and III is height above the surface on the radio altimeter.",[117,277,278,281],{},[28,279,280],{},"Forgetting the go-around dip on a CDFA."," Without a derived margin above the MDA, a go-around at the MDA can briefly bust it.",[117,283,284,287],{},[28,285,286],{},"Assuming the minima are the same for every aircraft."," They are built from the OCA\u002FOCH plus margins that vary by aircraft category and operation.",[20,289,291],{"id":290},"in-pilot-efb","In Pilot EFB",[10,293,294,295,299],{},"Pilot EFB is a study and planning companion for instrument approaches, helping you keep the gate-versus-floor distinction straight and read what each chart's minima box is telling you, alongside the ",[36,296,298],{"href":297},"\u002Flearn\u002Freading-an-instrument-approach-chart","approach plate"," and the rest of your offline-first briefing. It does not set your minima, read your altimeter, or make the decision, and the figures you fly come from the current chart and your approved minima. Pilot EFB is not a certified Electronic Flight Bag, so treat it as a study and planning aid and fly the approach from your official source of record.",{"title":301,"searchDepth":302,"depth":302,"links":303},"",2,[304,305,306,307,308,309,310,311,312,313],{"id":22,"depth":302,"text":23},{"id":65,"depth":302,"text":66},{"id":90,"depth":302,"text":91},{"id":108,"depth":302,"text":109},{"id":154,"depth":302,"text":155},{"id":165,"depth":302,"text":166},{"id":195,"depth":302,"text":196},{"id":221,"depth":302,"text":222},{"id":254,"depth":302,"text":255},{"id":290,"depth":302,"text":291},"2026-05-04",null,"The difference between a decision altitude and a minimum descent altitude, why one is a gate and the other a floor, and how DH and MDH fit in.",false,"md",[320,323,326],{"q":321,"a":322},"What is the difference between a decision altitude and a minimum descent altitude?","A decision altitude (DA) is a gate: on a precision or vertically-guided approach you reach it on the glidepath and decide whether to land or go around, accepting that the aircraft will dip slightly below it as the go-around begins. A minimum descent altitude (MDA) is a floor: on a non-precision approach you must not descend below it at all unless you have the required visual reference. So you may momentarily go below a DA during the missed approach, but you must never bust an MDA.",{"q":324,"a":325},"What is the difference between a decision altitude and a decision height?","Both mark the same decision point, but they are measured against different datums. A decision altitude (DA) is read on the barometric altimeter, referenced to mean sea level. A decision height (DH) is read on the radio altimeter, referenced to the height above the ground or the threshold, and is used for the lower categories of precision approach, CAT II and CAT III, where height above the surface has to be known precisely.",{"q":327,"a":328},"What lets you descend below the decision altitude or minimum descent altitude?","Having the required visual reference in sight and being in a position to land. The rules list the visual references that count, such as the approach lights, the runway threshold, the touchdown zone or the runway markings, and you may only continue below the minimum if you have the required references and can make a normal landing. Without them, you must go around at a DA or at the missed approach point on a non-precision approach.",[330,331,332,333,334],"A decision altitude is a gate you decide at, and the aircraft may dip slightly below it during the go-around.","A minimum descent altitude is a floor you must not descend below without the required visual reference.","A DA and MDA are read on the barometric altimeter above mean sea level; a CAT II\u002FIII decision height is read on the radio altimeter above the surface.","You may only continue below the minimum with the required visual reference in sight and a position to land.","The minima are built from the obstacle clearance altitude or height plus margins for the aircraft and operation.",{},"The difference between a decision altitude and a minimum descent altitude, why one is a gate and one a floor, and how DH, MDH and visual reference fit in.",true,"\u002Flearn\u002Fdecision-altitude-and-mda",[340,349,357],{"q":341,"options":342,"answer":347,"explanation":348},"On a precision approach, what is a decision altitude?",[343,344,345,346],"A floor you must never descend below","A gate at which you decide to land or go around, expecting a slight dip below it during the go-around","The height of the final approach fix","The transition altitude",1,"A decision altitude is the point at which you decide to continue or go around. The aircraft is expected to descend slightly below it as the go-around is initiated, and that is accounted for in the obstacle clearance.",{"q":350,"options":351,"answer":347,"explanation":356},"How does a minimum descent altitude differ from a decision altitude?",[352,353,354,355],"It is higher by exactly 200 ft","You must not descend below it at all without the required visual reference","It is measured by radio altimeter","It only applies at night","A minimum descent altitude is a hard floor: you must not descend below it unless you have the required visual reference. A decision altitude, by contrast, is a decision gate that the aircraft may momentarily dip below during the go-around.",{"q":358,"options":359,"answer":347,"explanation":364},"A decision height, as opposed to a decision altitude, is measured against what?",[360,361,362,363],"Mean sea level on the barometric altimeter","Height above the ground or threshold on the radio altimeter","The transition level","The aerodrome QFE only","A decision height is referenced to height above the ground or threshold and read on the radio altimeter, used for the lower categories of precision approach, while a decision altitude is referenced to mean sea level on the barometric altimeter.",{"title":5,"description":316},"fly-an-instrument-approach",4,[369,371,374,377],{"label":370,"url":75},"ICAO Doc 8168: PANS-OPS, Volume I (Flight Procedures, decision altitude and MDA)",{"label":372,"url":373},"FAA Aeronautical Information Manual, Chapter 5 Section 4 (Arrival procedures)","https:\u002F\u002Fwww.faa.gov\u002Fair_traffic\u002Fpublications\u002Fatpubs\u002Faim_html\u002Fchap5_section_4.html",{"label":375,"url":376},"FAA Instrument Procedures Handbook (FAA-H-8083-16)","https:\u002F\u002Fwww.faa.gov\u002Fregulations_policies\u002Fhandbooks_manuals\u002Faviation\u002Finstrument_procedures_handbook",{"label":378,"url":379},"ICAO Annex 6: Operation of Aircraft, Part I (aerodrome operating minima)","https:\u002F\u002Fstore.icao.int\u002Fen\u002Fannex-6-operation-of-aircraft-part-i-international-commercial-air-transport-aeroplanes","learn\u002Fdecision-altitude-and-mda","Operations","CiEmD2jLVbg2GSbicH3w23jNWPjTetpQ0f5vjm-X8ow",{"related":384,"newer":402,"older":408,"series":414},[385,390,396],{"path":386,"title":387,"description":388,"date":389,"topic":381,"draft":317,"minutes":367,"series":315,"seriesOrder":315},"\u002Flearn\u002Fv-speeds-explained","V-speeds explained","What the V in V-speeds means, the difference between a design limit and an operating speed, and a tour of the speeds a pilot lives by, from stall to Vne.","2026-06-20",{"path":391,"title":392,"description":393,"date":394,"topic":381,"draft":317,"minutes":367,"series":366,"seriesOrder":395},"\u002Flearn\u002Fthe-missed-approach-and-go-around","The missed approach and the go-around","The difference between a go-around and a missed approach, when each is flown, the climb gradient that protects it, and why going around early is wise.","2026-06-19",7,{"path":397,"title":398,"description":399,"date":400,"topic":381,"draft":317,"minutes":401,"series":315,"seriesOrder":315},"\u002Flearn\u002Fthe-global-reporting-format-for-runway-conditions","The Global Reporting Format for runway conditions","How the Global Reporting Format describes a contaminated runway: the condition code from 6 to 0, the assessment matrix, and the report split into thirds.","2026-06-17",5,{"path":403,"title":404,"description":405,"date":406,"topic":381,"draft":317,"minutes":367,"series":407,"seriesOrder":401},"\u002Flearn\u002Fcrosswind-components","Crosswind components","How to resolve a wind into crosswind and headwind components, a worked example, the sine rule of thumb, and what a demonstrated crosswind really is.","2026-05-05","plan-a-vfr-cross-country",{"path":409,"title":410,"description":411,"date":412,"topic":413,"draft":317,"minutes":401,"series":315,"seriesOrder":315},"\u002Flearn\u002Faltimetry-qnh-qfe-qne","Altimetry: QNH, QFE and the standard setting","What QNH, QFE and the standard setting do to your altimeter, the difference between transition altitude and level, and the EASA and FAA conventions.","2026-05-03","Weather",{"slug":366,"title":415,"part":367,"total":395,"prev":416,"next":421},"Fly an instrument approach",{"path":53,"title":417,"description":418,"date":419,"topic":381,"draft":317,"minutes":395,"series":366,"seriesOrder":420},"Non-precision approaches","What makes an approach non-precision, the VOR, NDB, localiser and RNAV types, why they use a minimum descent altitude, and how APV approaches sit in between.","2026-04-15",3,{"path":422,"title":423,"description":424,"date":425,"topic":381,"draft":317,"minutes":395,"series":366,"seriesOrder":401},"\u002Flearn\u002Fpapi-and-vasi-explained","PAPI and VASI visual glidepath","How the PAPI and VASI light systems show whether you are high or low on the approach, what the white and red lights mean, and the mnemonics for each.","2026-05-15",1782839404838]