alternate minima question

[ir1]

hi i will soon be starting my instrument rating. will be using jepps and have a question regarding alternate minima which i guess will be answered later on in training but just would like to know now.

when determining whether you need an alternate at a particular aerodrome, say essondon in this case. and just looking at weather, not lighting as i understand there are also conditions there.

it says that atc 303 3.2 one of the conditions is - more than sct below alternate minima.

now when determining which alternate minima to use do you

a, look at airport page for essendon which states the FOR FILING AS ALTERNATE say cat a with actual would be 910'

or

b, look at the approach which gives you the lowest mda / dh and compare with that.


eg. weather at essendon is bkn at 500'. because alternate minima is 910' you need an alternate, or is that 910' the minima if you were using essendon as an alternate.. can someone classify please


thanks

[chief wiggum]

look at the airport page and use the "for filing as alternate".
the "910' " given there is the cloud base below which you would NEED an alternate for EN.

Then of course, there is the question of "actual!"...

[Counter-rotation]

IR1
If I understand you correctly (I don't use Jepps but the concept is obviously the same) the answer to
"eg. weather at essendon is bkn at 500'. because alternate minima is 910' you need an alternate, or is that 910' the minima if you were using essendon as an alternate.."
is "both".;)
You cannot nominate as an alternate that which itself requires an alternate.
SO:
1) You want to go to Essendon.:ok:
You cannot go there without an alternate, if the forcast is as you describe (BKN005).:(
2) You want to go somewhere nearby, but use Essendon as an alternate.:ok:
You cannot do so if the forecast is as you describe (BKN005):(
Now let me just reiterate what Chief Wiggum has said above:
When you are in an exam room at a desk, and you are answering an exam question about this stuff, the correct answer is as per the book (obviously).
HOWEVER
When you are at work, briefing and preparing for a flight, whether you:
load that fuel, track via that point, carry that extra weight, go without this/that item serviceable (etc.) needs to be considered much more carefully. "The book says I can go" without further consideration,may very well get you :ouch: .

Know what's legal, but learn what's safe - they are not the same thing. Older, more experienced pilot's are very good for this sort of thing.

Happy IFRing!

CR.

[Capt Claret]

ir1
Using your example of Essendon, I think you're confusing Alt Minima with MDA/DA.

The Alternate minima is nearly always 500' ceiling and 2 km visibilty above the circling minima.

You state, alternate minima is 910'
910' is the CAT A circling minima based on actual QNH. It is 628' AAL but it is not the alternate minima.

The CAT A alternate minima at EN is found on the airport chart (Jepp 11-1) and is 1128' on actual QNH, which equates to 500' added to the circling minima of 628' (AAL). Additionally one would have to consult forecasts to determine which approach is likely, because the ALT Minima can vary with RWY and aircraft type/equipment.

So in summary, to determine whether one needs to carry an alternate, check the "For Filing as Alternate" boxes. To get an idea of the likelyhood of having to divert, compare forecast cloud base against instrument approach MDA/DA. The greater the difference, in general terms, the less likely you will have to divert.

ABOVE ALL REMEMBER weather forecasting is an inexact science.

Don't be tempted to not carry an alternate because the wx is just below the alt minima and you think it'll be ok.
Don't be tempted to not carry an alternate because every other time you did you didn't need it.
If your study of the wx coupled with knowledge of where you're flying tell you an alternate would be prudent, carry it if you can, or at least have a second option.


As an example, some years ago, CS-DN direct. No requirements on DN yet it was the start of the wet season. Full fuel carried because we could. Half way across the Gulf (of Carpentaria) radio traffic indicated aircraft holding at DN or diverting because of unforecast T/S. Thankfully we weren't affected, but we easily could have been. The storm was so violent it blew shipping containers off the wharf into Darwin Harbour.

[Agony]

Ir1

Couldn't agree more with the way the Capt summed it up, don't confuse the two. At the end of the day compare the forecast with the "filing for alternate" requirements and that will tell you what are required to do with respect to the rules.

However, as the Capt said, that meets the requirements and that can't be separated from making a decision on sound airmanship taking into account many factors. From experience, some people feel that they cannot add on extra fuel for "mum and the kids" particularly when the forecast doesn't dictate it. This can sometimes get sticky if it restricts payload, (pax, baggage, freight). Justify it to yourself and it should stick with the boss.

As stated the forecast is exactly that, and on longer flights it can change significantly. MEL for example, several times I have seen "no requirements" but looked at the Synopsis and Prognosis and dew point and taken more fuel because I felt the scurge of fog appearing after take-off. Sure enough it did and the majority of guys inbound diverted straight away. Luckily we had enough to hold and then land. Makes you feel good when you give a latest divert of 60-90 mins versus 5 mins to control.

Finally, the exam looks at requirements, life looks at reality,

Good Luck...........:ok:

[adam210]

Another question whilst on the IREX topic

In Jepp format, a STAR will give you an arc to fly, for example to the ILS. I say look at CS Biboohra 1 arrival, i notice that the arc shows the Lowest safe and then a T next to it, for example 5000T

what does that T stand for ?

[QSK?]

T=Minimum Obstacle Clearance Altitude (MOCA). Refer to the Jepps Legend section.