MDA vs DA | Minimum Descent Altitude and Decision Altitude Explained | Don't Bust Minimums!

if there's one single area where i've seen consistent failures on the ifr checkride it's in failure to follow altitude minimums on instrument approaches the disconnect is in distinguishing between a minimum descent altitude and a decision altitude and when to use each one for this reason i add into my brief on every approach whether the minimum altitude is an mda a minimum descent altitude or a d a a decision altitude let's look at an example to see the difference this is the ils or localizer approach to runway 3-3 right at baltimore the reason we call it the ils or look approach is because we're actually seeing two approaches in one approach plate if we duplicate the profile view of the approach we can separate how the approach is depicted for the ils only and for the localizer only here's what just an ils approach depiction would look like and notice we're only looking at the ils minimums at the bottom and here's the localizer only but with just those minimums we'll ignore the circling minimums altogether here but notice the other small differences between the two and let's examine each in detail starting with the ils an ils is flown by starting at an assigned altitude let's say in this case 3000 feet and intercepting the glide slope from below so when we start these are the instrument indications with the glide slope needle above center as we approach duds the needle starts to fall towards center indicating that we can descend along the glideslope we'll keep both the glide slope and localizer needle centered throughout the descent as we get closer to the runway now for this approach the minimum is 333 feet which because this is an ils is the decision altitude what this means is that we will continue the descent to 333 feet and at that point decide if we have the required visual cues to continue to descend down to the runway if we don't we'll decide to execute the missed approach now here's the thing because we've made this decision at 333 feet as we're executing the mist we will by necessity descend below the decision altitude due to the delay in setting up the climb and just through our own momentum so here we momentarily pass below the da as we start the climb out to the mist this is right and proper and perfectly allowable when flying a precision approach or an rnav approach with vertical guidance such as an lpv the point of a decision altitude is as the name suggests to be a decision point it doesn't represent a hard minimum let's contrast that with the non-precision localizer only version of this approach here we have no vertical guidance so we identify the various fixes on the approach using our dme once again we'll start at 3000 feet when cleared for the localizer approach we'll be looking for 12 dme which indicates the duds fix when we can descend to our step down altitude of 2000 feet the next fix oriole is the final approach fix as noted by the maltese cross and is at 5.8 dme so we'll maintain 2000 until then then start the final approach the next fix is x-eve at 2.5 dme and 940 feet from x-eve we'll continue descending down to the minimum descent altitude mda of 540 feet the word minimum here means that we can't go below until we're in a position to land the next point the 1.3 dme is the visual descent point as noted by the black triangle this is where we can make a normal descent to land from the mda so if we don't have the runway in sight by then we should decide to go mist however we still need to maintain the minimum altitude of 540 feet all the way and delay actually executing the missed approach until we get to the missed approach point at which point we can start our climb out so let's summarize these differences on the ils a precision approach you decide to go mist at the decision altitude in this case 333 feet you're allowed to descend below the da briefly as you execute the missed approach on the localizer a non-precision approach you could decide to go mist at any time on the approach the vdp is a good indicator of when to make that decision since that's the point where you can make a normal descent to land from the mda so you can't go below the mda at any point on the approach hence the word minimum in minimum descent altitude the execution of the mist has to happen at the missed approach point let's end with a reading from the instrument acs which is the playbook for how your trek ride will be evaluated for the precision approach you need to maintain no more than a three-quarter scale deflection of the vertical and lateral guidance so as long as you're on the needles you're okay no mention of minimum altitudes the non-precision approach standards on the other hand require you to maintain the minimum descent altitude with a buffer of plus 100 feet and minus zero feet in other words going below the mda even a little bit can earn you a bust on your check ride so when they say minimum they mean it you do get a 100 foot buffer above the mda though so why not use that give yourself a bit of cushion this is a very common item that gives instrument students trouble so the best antidote i have is to make sure you're clear about the difference between the decision altitude and the minimum descent altitude and actually incorporate this piece into my brief so i'm ready to fly the approach the way it's supposed to be flown so if it's the localizer approach i'll say for example this is a non-precision approach which means i'll start the final approach at oriole and descend down to 540 feet which is the mda make sure you're incorporating this brief on an rnav approach as well on an ils or loc it's fairly easy to tell whether you're flying to a da or an mda on a gps approach you'll need to know what kind of guidance you're flying this approach lists different minimums based on different approach guidance the lpv and lnav vnav approaches use vertical guidance so they give decision altitudes of 343 feet and 432 feet the lnav approach uses only lateral navigation so it gives an mda of 600 feet you'll know which type you're using by looking at the indication on your gps unit during the approach you would also be familiar with your equipment whether or not it was able to do an lpv approach for example far too often i've seen pilots descend to the decision altitude for the lpv which in this case would be 343 feet when they're doing an lnav approach and should have stayed at the minimum altitude of 600 so make sure you're briefing these if this was helpful please click subscribe so that you could stay up to date on every new training video coming out each tuesday and friday and get access to posts and articles that will take your training even further it just takes one click and it's so worth it

Channel: FlightInsight

Views: 173,229

Keywords: MDA vs DA, Don't Bust Minimums, decision altitude, decision height, rnav approach, missed approach, minimum descent altitude, approach plate, gps approach, decision altitude vs mda, approaching decision height, decision altitude vs decision height, decision altitude and minimum descent altitude, what is decision height in aviation

Id: 9ppYg_ZxHfI

Length: 7min 4sec (424 seconds)

Published: Tue Aug 31 2021