WHY DIFFERENT MDA FOR CIRCLING APP ON RECIPROCAL R/Ws
 

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 ?:ugh:

thanx in advance

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

stubby1:

Do you have a specific example?

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.

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.

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

d105:

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.

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.

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...

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

- why not ask to stay in the circuit?

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.

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

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.:hmm:

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

- 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!

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.

Stubby - you there? Example please!

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.

As Centaurus stated And as Tinstaafl has also stated, 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

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 ???:ugh:

I can only access the AIP charts and they look as if they have been done by a six-year old! The VOR26 is designated 'CAT A/B' but has minima for CAT C. NDB 26 is designated 'CAT A/B/C' but does not show any minima for CAT C (finger trouble?)

It appears that CAT A/B you circle on 08 from the VOR using a DA of 890'.
Cat C/D you cannot operate in at all!?? There do not appear to be any charts.

CAT A/B you circle on 26 from the VOR using a DA of 680' Cat C/D 890'
Using the NDB for some bizarre reason you use a DA of 680' CAT A/B and I would GUESS 840'for CAT C/D (Which I suspect is a chart error!)

Good luck! It would be useful to see what JEPP/AIG make of this.:ugh:

for the RWY 08 circling 26 is only available for cat A & B aircraft that's it. Use the associated minimas. :ok:

Jepp charts:

http://terps.com/vobz/VOBZ%20Jepps.pdf

Hmm. Still confusing, but Jepp have done well considering the source material!

I really cannot see why circling differs between runways under PANSOPS. There are no obvious obstacles.

Any idea why Cat C is so restricted?

coz even the straight in approaches are restricted to A&B only. Only NDB RWY 26 is authorized for cat C. I guess it's due to large offset between the RWY and final courses :ok:

Cannot see the logic. Cat C could easily circle off the 08 VOR.

Aterp - need some assistance here - what is 'FN26' on the NDB proc and the '4.3' and 3 degree slope - are we looking at PRNAV?

BOAC:

It wouldn't be the first time PANS-OPS has been tortured by a less than sterling procedures staff.

That is an On-Airport, No-FAF NDB IAP. Jeppesen has coded a sensor FAF for LNAV (RNAV), thus FN26. They have also coded a 3 degree VNAV path from FN26 to a 50' thresold crossing height. It is 4.3 miles from FN26 to the threshold.

1) Roger!

2) Is there a reference for the use of 'FN' - I suspect it is a TERPS point rather than a PANSOPS point, and should that chart not be annotated 'RNAV or perhaps 'APV(Baro)' in PANSOPS? I've been all over Jepp (on-line) and have not found anything.

BOAC:

Any time a fix is in bracketts [FN26] it is a CNF; computer navigation fix. This is in the domain of RTCA and FMS engineers. It is neither TERPS nor PANS-OPS; rather it is a method of doing an FMS overlay of any ground-based procedure. If the state (India in this case) does not authorize RNAV overlay of the procedure per se, then it goes to the operator's authorization whether or not the underlying nav aid must also be monitored while flying the LNAV (RNAV) overlay.

Thanks for the clarification - I take it it would 'exist' in the Jepp NAV database then? Is there a Jepp pdf or whatever explaining?

timed approach must be flown conventionally however aided by a FMS way point to commence the descent, quite few of them still out there. We don't have the approaches in the data base only the FN way point for aid the identification of descent point. :ok:

- only one problem with that!

BOAC:

This graphic shows two references I found in the Jepp legend. The bottom graphic is the procedure loaded into the Garmin G-1000 trainer, which uses the same nav data as the actual hardware:

http://i201.photobucket.com/albums/a...rpster/CNF.jpg

Again thanks - I am familiar with 'ff05' but not 'FN' - I assume there is no significance to a pilot in the different lettering - 'ff' / 'fn'? I see also it does refer to a 'Jepp NavData waypoint'.

Incidentally, I reckon that Garmin database is incorrect - it shows 4.3 to the 'map' which is actually the BZ? How can the MAP be the BZ anyway with only a 2 degree track change from THLD? In fact, where IS the MAP on an RNAV approach like that? Surely if the idea is to fly a CDA at 3 deg the MAP must be on the approach track at 680/890 (not 490!)? It looks like someone in Jepp is as confused as I am:). I do hope that is not the actual database for NDB26 at VOBZ or there may be tears!

Is 'RW26' actually south of the threshold in the database?

BOAC:

Highly unlikely that Garmin's database is any different from any other FMS that uses Jeppesen data.

The legal MAP is the NDB, which is 1.1 miles beyond the threshold. Why they coded a different MAP is beyond me. There are many of these remaining in the U.S., (VOR or NDB overlays) but when there were Jepp didn't move the MAP.

The reason is that circling minima can never be less than the straight-in minima. Consequently, differing minima for the runway approaches may result in the circling minima being raised for one runway only.

Circling minima are calculated independently of the navigation aid used, and have different obstacle clearance requirements and a fixed visibiity requirement.

Straight-in minima are determined dependent on the navigation aid used, and visibility requirements may vary dependent on visual aids available and the MDH. If these are greater than the equivalent circling minima, the circling values must be raised.

Aterp - if that is a genuine Jepp product you have screenshot then there is a serious error which needs addressing with great urgency. The MDA is dangerously wrong!

Still no logical explanation from anyone for two different circlings at VOBZ. Is it just a co-incidence that the CAT C circling alt for 26 is the same as the VOR minima CAT A/B for 08? Bizarre!

We have FDs here as well.

We have numerous examples of this here in Oz. I believe Jepp codes it that way because they assume, as it is a runway approach, you will not be circling after passing the threshold and not Visual. Therefore the runway threshold (RW26) is coded as the "end" of the approach although our coding also has the navaid after RW waypoint, then the MA climb.

Of note is that the database track from the "FAF" waypoint eg from FN26 to RW26 will not be the charted track if the navaid is offset. Because of an ARINC rule ("if FF, RWY and MAPt all lie within 0.14nm of the same track"), Jepp are able, and do, code direct to the RW26 waypoint from FN26. Obviously, if the navaid is offset, the flown track will diverge from the charted track, with the aircraft tracking "straight" at the threshold whilst being offset (requiring a double-turn when Visual), instead of crossing the centreline at around the MDA on the charted track, requiring only one turn onto final. Practically, this can be a real problem as the crew is presented with a significant double-turn to get lined up on final after becoming Visual.

BOAC:

The two VOR IAPs don't have an altitude coded at that point. Why the 490 on the NDB is beyond me. It does seem to be a coding error. Nonetheless, a properly trained crew is to predicate MDA on the chart, not anything in the database.

That is a question only the Indian procedures design staff could answer.

Capn Bloggs - useful stuff there. I hope, however, in Oz you have the CORRECT DA in your coded approaches:sad:

Sure gets complicated when you 'twist' an offset approach into a straight-in for a computer - how do you GET to the MAP if it is the NDB and if it isn't, how is the obstacle splay affected by 'moving' the MAP to either the threshold or abeam the NDB?

Presumably if you went round off Aterp's VOBZ NDB26 you would need to go left to pick up the NDB 250 track - or would you just fly the 'RNAV' track to the north of the correct track? My head hurts.