Erfandean
Topic Author
Posts: 9
Joined: Tue Oct 10, 2017 4:27 pm

DH/A and MAP

Sat Dec 02, 2017 12:37 pm

is DH/A (decision height/altitude) ALWAYS at the same point as MAP (missed approach point)?
basically are their altitude or height the same ALWAYS?

i'm asking because i have heard that they could be at different altitudes (height) which makes me confused because DH/A IS the altitude whether to continue or preform go-around and i think i've seen a approach chart where they're not the same altitude but again i'm not sure.
 
T1a
Posts: 14
Joined: Tue Apr 24, 2012 5:41 pm

Re: DH/A and MAP

Sat Dec 02, 2017 1:04 pm

Procedure wise the Missed Approach Point in the point where the final approach segment ends and the missed approach segment of the approach starts.
Now you need to distinguish between the MDA (minumum descent altitude) of a non-precision approach and the DH/A of precision appoach.
On a NPA you will always find a MAP that is defined in some way. It may be a DME distance, an RNAV point, the beginning of the runway, or simply timing. Now, procedure wise you can do an old-school "dive an drive" approach on these approaches. That means, you fly down to the MDA an fly along the MDA until you hit the MAP, if you get the runway in sight before arriving at the MAP you may land, otherwise you have to go around. On these approaches a defiened MAP is needed.
On a precision approach you usually don't have a defiened MAP. It is substituded by the DH/A. As soon as you hit the DH/A without having the visual reference, you execute the missed approach. Now this approach design becomes tricky when you initiate a go-around farther from the field for any reason. You will be very high very early and if the first turn in the missed approach in based on an altitiude you might turn very early. Therefore quite a number of PAs have things like "no turns prior to 1 DME west of the field" spelled out in the missed approach procedure.
But you are right, on pretty much all ILS approaches you have multiple DH/A depending on aircraft or approach category in use. Therefore there is no fixed MAP.
 
Passedv1
Posts: 528
Joined: Sun Oct 07, 2012 3:40 am

Re: DH/A and MAP

Sat Dec 02, 2017 1:54 pm

Erfandean wrote:
is DH/A (decision height/altitude) ALWAYS at the same point as MAP (missed approach point)?
basically are their altitude or height the same ALWAYS?

i'm asking because i have heard that they could be at different altitudes (height) which makes me confused because DH/A IS the altitude whether to continue or preform go-around and i think i've seen a approach chart where they're not the same altitude but again i'm not sure.


A DH/DA and a MAP are two completely different things.

A DH/DA is an altitude and a MAP is a lateral fix (think point on a map).

A DH/DA is an altitude an aircraft on an instrument approach will fly down to before executing a missed approach if they don’t get the field in sight.

A MAP is the lateral point where if an aircraft reaches the MAP the airplane will start the missed approach if they don’t have the runway in sight.


To answer your first question, the answer is no they are not always the same point.

It is quite common for the points to be different on a non-precision approach. The aircraft will descend to the DH/DA, if they don’t get the runway in site by the time they reach the DH/DA then they will start climbing to the missed approach altitude. They will continue inbound toward the field on the approach though, until they reach the MAP and begin the lateral navigation of the published missed approach.

You have a DA of 500’. The MAP is located at the VOR which is located on the field. The missed approach calls for an “immediate right turn to 180 degrees climb to 5000’). Once you are established on final you start down to 500’. You watch the distance to the field tick down 5mi, 4, 3...just as you get to 500’. You look out the window and you don’t see the runway. Per the missed approach instructions you start climbing to 5000’. You don’t start your “IMMEDIATE right turn to 180 degrees” until your DME gets to 0 which in this scenario is still 3 miles in front of you.

As to your 2nd question, there is no altitude specific to the MAP. The MAP is a lateral point. Depending on the scenario, you could be above your minimums, at your minimums, or even below minimums if you had the runway in site, descended to land and then subsequently lost site of the field.

Hope this helps.
 
Erfandean
Topic Author
Posts: 9
Joined: Tue Oct 10, 2017 4:27 pm

Re: DH/A and MAP

Sat Dec 02, 2017 2:58 pm

I pretty much got my answer, thank you guys :)

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