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RNP Approach

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RNP Approach

Old 5th Mar 2021, 14:53
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RNP Approach

In several RNP Approach charts I have noticed that the 'M" Missed Approach Point is at Runway Threshold. If an aircraft is allowed to fly level at MDA till Runway threshold in this case, how can a landing be accomplished in the Touch Down Zone? Or am I missing something very obvious? Thanks in advance.
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Old 5th Mar 2021, 15:07
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The Missed Approach Point does not have any connection to the landing itself. He just defines where the Missed Approach Procedure starts. For landing you have to be able to land in the TDZ within your company's operating limits. (e.g. max rate of descent 1000 ft/min).
So, if the MISAP is at ray threshold, your descent for landing has to start earlier.
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Old 5th Mar 2021, 15:20
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The missed approach point has nothing to do with whether you can or can’t land. Like the above mentioned it’s simply where the missed approach starts or the earliest a turn can be established in the G/A.
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Old 5th Mar 2021, 15:28
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In case of a 2D approach (to LNAV) minima yes. 3D approach (LNAV/VNAV or LPV) minima require you to commence a missed approach at DA. That being said, for commercial operations under EASA, all NPAs should be flown as a CDFA, which means go-around shall be commenced at DA or MAPt, whichever comes first.
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Old 5th Mar 2021, 15:33
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1) In many legislations level flight upon reaching the MDA is forbidden, for quite some time.

2) On some installations (such as the type the OP is most familiar with) it is the technological limitation of FMS which needs to have MAPt coded at RWY THR with a hard constraint of 50' TCH in order to properly calculate the VNAV path. Especially the segment below MDA.

I think the 1) is actually quite obvious, called CDFA. Sorry for being blunt.
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Old 5th Mar 2021, 16:52
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Originally Posted by FlyingStone View Post
In case of a 2D approach (to LNAV) minima yes. 3D approach (LNAV/VNAV or LPV) minima require you to commence a missed approach at DA. That being said, for commercial operations under EASA, all NPAs should be flown as a CDFA, which means go-around shall be commenced at DA or MAPt, whichever comes first.
This is a fine, but important point of distinction. Vertically, the missed is commenced at crossing DDA (if reached before the MAP). Laterally, it's commenced at the MAP. (At least in TERPS land)
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Old 5th Mar 2021, 23:43
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If an aircraft is allowed to fly level at MDA till Runway threshold in this case, how can a landing be accomplished in the Touch Down Zone?
If you were circling to land.
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Old 6th Mar 2021, 08:41
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As I understand it here in Oz, the MAP at RW gives the designer of the procedure a known point to chart the G/A. Most modern approaches are CDA and tracking to the MAP does not need to be level, in fact it would be dumb to do that. Climb as hard as you can when the decision is to miss the approach and get away from the ground.
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Old 6th Mar 2021, 12:11
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Originally Posted by oggers View Post
If you were circling to land.
CTL is not charted on RNP AR IAPs.
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Old 6th Mar 2021, 16:34
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I got the feeling the OP was referring to what the FAA calls a GPS or RNAV approach. I understand the naming convention is in a state of flux right now though.
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Old 6th Mar 2021, 18:06
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[edit: yes what check airman said]

Originally Posted by aterpster View Post
CTL is not charted on RNP AR IAPs.
That's as may be, but he did not specify RNP AR he wrote "RNP Approach". Your common or garden "RNAV (GNSS)" is an RNP approach these days and there are plenty such approaches with circling minima. AR approahes are titled "RNAV (RNP)", which actually means RNP AR, as opposed to just RNP. This terminology is confusing but it is what we have to get used to.
"This fact sheet will focus on the most common navigation specification called “RNP Approach (RNP APCH)” and titled Area Navigation (RNAV), “RNAV (GPS) Rwy XX"....The other approach navigation specification, or set of aircraft and aircrew requirements needed to support a navigation application within a defined airspace, is reserved for complex airspace and called RNP Authorization Required Approach (RNP AR APCH) which are titled “RNAV (RNP) Rwy XX"
FAA Factsheet RNP Approaches

Last edited by oggers; 6th Mar 2021 at 18:16.
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Old 6th Mar 2021, 20:58
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Check Airman

Might depend on charting company as well, no idea there. in my route manual everything that used to be an RNAV/GNSS or similar approach is now simply a RNP approach. RNP AR would be what aterpster means, RNAV approaches are still in the manual, but those (only checked a few) are all RNAV Visual or similar kinds of approach, with an initial RNAV part and then a final visual part. Since we are not RNP AR certified yet, there are none of those in our route manual.
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Old 7th Mar 2021, 12:27
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Smile

Check Airman

You are correct. My brain saw "AR" not my eyes.
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Old 12th Mar 2021, 11:08
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Originally Posted by Vessbot View Post
This is a fine, but important point of distinction. Vertically, the missed is commenced at crossing DDA (if reached before the MAP). Laterally, it's commenced at the MAP. (At least in TERPS land)
That's correct. Missed approach procedure has two aspects lateral and vertical. Vertical starts at minimum and and lateral starts at or after MAP.
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