WHY DIFFERENT MDA FOR CIRCLING APP ON RECIPROCAL R/Ws

[stubby1]

hi

I understand that MDA for circling approach is applicable subsequent to an airfield app aid instrument procedure (non electronic glide path).

Then on breaking off from lets say 09 VOR app I can choose to circle to land on 09 ( if straight in criteria not met) or 27.

How come then on some app plates there are different MDA for circle to land for 09 & 27.

Am I missing something ?

thanx in advance

[Centaurus]

Depends on the position of the critical obstruction that affects each runway. Quite common to see different circling MDA for each runway.

[aterpster]

stubby1:

I understand that MDA for circling approach is applicable subsequent to an airfield app aid instrument procedure (non electronic glide path).

Do you have a specific example?

[aslan1982]

I think it has to do with flying the missed approach procedure for the the initial Instrument Approach.

For example at Dublin

Flying the VOR approach to 16 for a circle to land at 34

We set the minimas for 16 as this was the approach we flew and it will be the go around procedure we follow at any stage during the procedure.

The go around for 16 is climb on track 155 degrees to Killiney climbing 3000feet

Whereas the go around for 34 is climb straight ahead to 3000 and contact ATC

So even if we are at 300 feet on finals to 34 and ATC say go around we must follow the procedure for RW 16 which is climb turn and track 155 to killiney.

I know at dublin the circle to land MDAs for 16 and 34 are the same but maybe this might help

I hope I understood ur question right.

[Capn Bloggs]

Depends on the position of the critical obstruction that affects each runway. Quite common to see different circling MDA for each runway.

Dunno about that, Centaurus! The PANS-OPS circling area is defined as tangents joining arcs from each threshold. I reckon there can't be an obstacle that is unique to only one runway's circling approach as the circling area as defined applies to all runways.

[d105]

At some airports the circling minima's are different because of neighbouring noise sensitive zones.

[aterpster]

d105:

At some airports the circling minima's are different because of neighbouring noise sensitive zones.

That, and more typically, a high obstacle that can be isolated by sectorizing circling minimums, or even prohibiting circling in a particular sector. But, the procedure makes this clear.

[sevenstrokeroll]

and some procedures don't authorize circling to one side, EG: south of runway, why not take a look at dozens of approaches, especially in mountainious areas.

[FlightPathOBN]

Hold patterns can be an art form in procedure design. There are many, many variables.
Sometimes the MDA is set using terrain/obstacles, ATC may set the MDA for conflicts, and other times, it will be set to help facilitate the approach MVA.
There are numerous hold pattern templates (the FAA has 31 hold patterns) to use, driven by aircraft class, altitude, and holding speeds/turn radius/bank angle limitations, therefore the size of the hold pattern may also drive the MDA.
There are also engine out hold patterns...

[BOAC]

Originally Posted by aslan1982

We set the minimas for 16

- well, if you did that in the UK you would have your bottom smacked!

So even if we are at 300 feet on finals to 34 and ATC say go around we must follow the procedure for RW 16 which is climb turn and track 155 to killiney.

- why not ask to stay in the circuit?

[Capn Bloggs]

Obstacles and Noise areas are only going to force different MDAs if you mandate a particular circuit direction. For example, if there is an obstacle to the east of the runway, then all circling could/would be at the same MDA on the western side, regardless of landing direction.

[Pitch Up Authority]

Interesting

Although the MDA is based on obstacles within an area defined by tangents connecting circles draw around the runway thresholds, it occurs to me that the obstacle clearance of the let down procedure itself also interferes.

With this in mind you could expect a different circling MDA, limited by a VOR let down Rwy 09 circling 27 then on an ILS let down 27 circling 09.

I am puzzled

[stubby1]

aviators
am still perplexed. Assume a vor proc which breaks off at an angle to r/w.

First is it not true that shooting vor app for r/w 09 , when i break off at MDA I have a choice of circle to land on 09 or 27(where straight in not possible ).

Now the vor char for 09 on which i did the procedure gives me a circle to land min. should i use it to cicle to land on 27 or 09 itself

Added to this is my Q, why then have diff min.

[aslan1982]

BOAC

- well, if you did that in the UK you would have your bottom smacked!

So what minimias do you use. In the case of Dublin for example

So even if we are at 300 feet on finals to 34 and ATC say go around we must follow the procedure for RW 16 which is climb turn and track 155 to killiney.

- why not ask to stay in the circuit?

we must follow the procedures in our ops manual. We cant just do half a go around into a visual circuit. Well its not recommended.

In our circling approach for a go around we make a climbing turn in the shortest direction towards the landing runway and execute the missed approach

[BOAC]

So what minimias do you use.

- circling minima like most do.

I would suggest that to fly a full IFR g/a from `1 mile visual final WITHOUT asking to stay in the circuit is bordering on madness!

[Pitch Up Authority]

Stuby1

I agree. What I meant is that the MDA of a NP might be higher than the MDA based on the obstacles in the circling area. For example a NP based on a VOR that is not on the field in combination with a low intensity approach light system.

This might explain why the circling via an ILS on 27 might bring you down to an MDA based on obstacles within the circling area while the VOR on 09 is not able to bring you down to the same MDA as the ILS.

I am just trying to figure out where the original question is based on.

[BOAC]

Stubby - you there? Example please!

[Tinstaafl]

I'd say varying circling minima can be due to a number of obstacle and/or navaid constraints. There are limits to the gradients allowed for different sections of the approach so an obstacle from one direction on final could impose a limit that doesn't occur from another direction. MDA has to allow for the missed approach gradient so an obstacle could intrude into one runway's missed approach but not into another's.

Approach type could make a difference too. Different approaches have to consider different tolerances leading to different obstacle considerations.

[blackburn]

As Centaurus stated

Depends on the position of the critical obstruction that affects each runway. Quite common to see different circling MDA for each runway

And as Tinstaafl has also stated,

an obstacle could intrude into one runway's missed approach but not into another’s

The MDA whether for a circling approach or a straight in approach is firstly dependant on the critical obstacles affecting either the approach or the missed approach gradients. The critical obstacles are often not the obstacles within the circling area for the particular performance category of aircraft. However once visual an aircraft on a circling approach is then subject to the rules applying to vertical obstacle clearance along the flight path and the visibility criteria determined by the procedure designer.

Hope this helps clarify the problem.

Blackburn

[stubby1]

FRIENDS

Pl look up vor for 08 & 26 VOBZ vijaywada. (how do i get the figure on this mail ?!!)

If i were to break off from vor 08, & circle to land 26, which MDA do i use for cirling. I am following the vor 08 chart & it gives me ;x; height for circle to land. but then the vor 26 chart gives me :y: height.

Guys , as the chart for 08 is in front ,i guess i should follow circling ht i see on it...x: ...but aint i doing circling for 26 ?? shud i flip the chart to vor 26 to take the circling ht :y:


AM TRULLY FOXED. WHAT WUD U DO ???