Straight in & circling vis minima

[jsmitty01]

Looking through some approach charts, for my category A & B aircraft I was wondering why the visual minima for a straight in landing is usually more than the visual minima for a circling approach for the same runway?

[The Messiah]

The idea is that you can see the landing environment from the minima and basic trigonometry requires greater vis for a straight in than from within the circling area.

I think thats right.

[DeltaSix]

JSMITTY01

Which instrument approach plate are you referring to ? Maybe I haven't been paying attention to it but I thought that the minima for a circling would usually be higher than a S-I as you need to circle around.


D6

[Ricky Bobby]

DeltaSix,

It seems to be more a case of which approach has a circling VIS minima which is actually higher than the straight in VIS minima? I cannot find one for a CAT A & B aircraft. This was pointed out to me by an old crusty ATO on a renewal, he caught out an FOI who did not realise this.

Some examples-

Coffs Harbour VOR, RWY 03.
Straight in=4.2
Circling=2.4

Goondiwindi NDB, RWY 04
Straight in=3.3
Circling=2.4

Halls Creek RNAV, RWY 22
Straight in=3.5
Circling=2.4

Apart from ILS's.

[Howard Hughes]

These things always make me laugh, how do you measure these distances from the cockpit anyway? If it's safe to land you do, if it's not, you don't! Simple as that...:hmm:

[DeltaSix]

Ooopsss, sorry my bad, I was thinking of the MDA... :ugh:

[neville_nobody]

This would be your answer:

CAAP 178-1(1) Page 11

"In order for a successful straight-in approach and landing to be conducted, the pilot of an aircraft conducting a runway approach must be able to see the runway prior to or on reaching the MDA. The visibility published on Australian charts is determined by calculating the distance from the runway threshold to the point on a normal 3° descent path at which the MDA is intercepted. A margin of 160m is added to that distance to allow visual reference to a reasonable amount of runway. Visibility for a straight-in approach therefore varies only with the height of the MDA above the runway.Visibility for circling operations varies with aircraft category. It is based on the radius of turn that an aircraft in each category would require in adverse wind conditions to manoeuvre from a downwind position to align with the landing runway."

[Grog Frog]

OK
Canberra 17 VOR/DME Cat B, no circling permitted as the MAP is outside the circling area.
MAP is 3.5 DME or 4.1 nm from Runway 17 threshold.
Required vis from the plate is 5.0k., yet MAP is around 7.0km from the landing threshold.
With minimum viz how can you legally continue the approach from the MAP ??
Furthermore, T-VASIS are not mandatory for night ops, how then do you conduct a stable descent from the minima (3250ft) which is 1450+ agl, at night when again the MAP is outside the circling area.
Any CASA chaps/ chapesses or procedure designers out there that can help:confused:

[BurglarsDog]

GF

Normally when someone asks such an intelligent question there is complete silence - so dont hold your breath for a reply from CASA!

Be careful though. In Oz the difference between accurate feedack and perceived criticism is labelled as winging... you know what happens to the wingers!! They normally loose the cricket!!

DogGone:)

[alphacentauri]

GF,

I agree that Canberra is an anomoly and here is why.

Since the min vis for flight under the VFR is 5000m then there really isn't any point in publishing a vis higher than 5000m for any aerodrome. If a vis of 8000m was published then in order to fly the approach the vis dictates that you would be in VMC anyway....So you have to be in VMC to fly an IFR approach....make sense? :confused: :confused:

Basically the maximum visibility that can be published for any aerodrome is 5000m, because this is the min vis for flight under the VFR.

So in the case of Canberra, if the vis was not below 5000m aren't you flying in VMC anyway? and so you can continue the approach, is that right?.....I am not familiar with ops at CB so excuse my ignorance if I am wrong.

Alpha