Another IFR alternate question - re: PROB

cargo_guy · Post by **cargo_guy** » Tue Dec 06, 2005 2:32 pm

Scenario:

TAF HAMILTON AIRPORT, ON
CYHM 061740Z 061818 12015G25KT P6SM BKN040 PROB30 2024
1/4SM +SHRA. NXT FCST BY 00Z=

RWY 12 is served by a straight in ILS (200-1/2).

Assuming your planned arrival at CYHM would be 22Z, can you use it as an alternate?

I say yes. What say you?

Here is my reasoning:

According to the AIM RAC 3.14:

the forecast PROB condition shall not be below the appropriate landing minima for that aerodrome.

Now, my first instinct was to say: "No! It can't be used as an alternate because the 1/4SM is lower than 1/2"

But, according to AIM RAC 9.19.3:

CAR 602.128 specifies that landings are governed by published DH/MDAs...

Furthermore,

Published landing visibilities associated with all instrument approach procedures are advisory only.... They are not limiting....

Hence, the 1/2sm is not part of the landing minima. Therefore, even though the Prob condition states 1/4sm, you can still legally use CYHM as an alternate in this case.

Discuss amongst yourselves. KAG jump in here, I'm interested in hearing what you have to say.

Peace out!

Cargo_guy

springjob · Post by **springjob** » Tue Dec 06, 2005 2:46 pm

I don't thin you can, alternates are for planning purposes, in this case it would be 600 - 2 or 300 - 1 above HAT which you don't have because of the prob (vis 1/4 sm).
Now once you are in the air you go whever you want...

snag · Post by **snag** » Tue Dec 06, 2005 2:59 pm

Good question,

Common sense would say that you would take the visibility into account as well, but you are right, everwhere I look, including the IPM, it says under "Landing Minima" that it is governed by DH/MDA's and published vis is "advisory only". This tells me that you are good to go.

Also leads to a parallel question. If my company is approved for RVR1200 takeoffs, as long as the ceiling is ok, do I need a take-off alternate when the vis is that low and the recommended vis is 1/2sm for landing? hmm...

jackrabbit · Post by **jackrabbit** » Tue Dec 06, 2005 3:03 pm

I don't think you can. You would need the 1/2 mile posted on the approach.
Vivsibilities do matter in certain situations, such as an approach ban as well as take off, taking off below landing minima (needing a take off alternate) and picking alternates. Like you stated, the prob condition will not be below the landing minima.

cyyz · Post by **cyyz** » Tue Dec 06, 2005 3:09 pm

expect to reach the alternate at 1959... problem solved..

snag · Post by **snag** » Tue Dec 06, 2005 3:12 pm

Vivsibilities do matter in certain situations, such as an approach ban as well as take off, taking off below landing minima (needing a take off alternate) and picking alternates

1200RVR does not violate an approach ban. If my ceiling is 300 AGL (for example) at the same time, I am not (in theory) below any landing minimas.

groundtoflightdeck · Post by **groundtoflightdeck** » Tue Dec 06, 2005 3:16 pm

Thats a strange TAF, I would expect that +SHRA would bring the ceilings down significantly, which would start to affect alternate criteria.

springjob · Post by **springjob** » Tue Dec 06, 2005 3:30 pm

If you are in the air coming to your alternate, the normal approach ban rules apply. So it does not matter what the TAF says as long as you have an RVR of 1200' you can land.

altiplano · Post by **altiplano** » Tue Dec 06, 2005 4:01 pm

BTD · Post by **BTD** » Tue Dec 06, 2005 4:19 pm

Cargo Guy I believe that you are correct in your reasoning. The prob condition only limits if it is below your landing minima.

It also only makes sense that landing visibilities in the CAP are advisory only. All CAT I ILS' have an RVR value of 2600(1/2sm) or higher. If they were limiting, an approach ban wouldn't be required except for CAT II and III which have their own rules anyway. As long as you are above 600-2 or 300-1 above the DH-recommended vis which ever is higher in the normal change period of the TAF you are good to go.

Whether you want to or not is a different story.

But that taf looks strange with P6sm and BKN 4000 then probablilty of 1/4sm out of nowhere. But I guess stranger things have happened.

turbo-prop · Post by **turbo-prop** » Tue Dec 06, 2005 4:19 pm

No, cause for an alternate you would need 300-1 as it is the only precision approach, and the prob falls in yourt time frame.

BTD · Post by **BTD** » Tue Dec 06, 2005 4:20 pm

oops meant BKN040

BTD · Post by **BTD** » Tue Dec 06, 2005 4:22 pm

He never said it was his destination. Just his planned arrival, I would assume he meant if he had to go there.

BLZD1 · Post by **BLZD1** » Tue Dec 06, 2005 4:40 pm

You can not use the above as an alternate because of the ¼ mile vis. You use the suggested VIS and HAT for calculating all types of alternates. (T/O ALTS and LDG ALTS)

Example: You are using an airport with an ILS with mins of 350AGL (due to mountains) ¾ mile vis suggested.

To use this as an alternated assuming it is the only approach at the airport. The ceiling would have to be 700AGL and 2 Miles vis in the TAF.

If the TAF was VFR and had a PROB of 400 and a ½ at your arrival time then it would not qualify as an alternate because you need be 400 AGL and ¾ Vis. If PROB is being used then it must meet both HAT and Suggested Vis. landing weather limits on the approach chart.

altiplano · Post by **altiplano** » Tue Dec 06, 2005 4:51 pm

BLZD1 · Post by **BLZD1** » Tue Dec 06, 2005 5:10 pm

Then why do you use them to calculate normal Alternate limits?

600-2 or Add 300-1 Which ever is greater Prec.
800-2 or Add 300-1 Which ever is greater Non Prec.
400-1 or Add 200-1/2 Which ever is greater 2 Prec. and 2 Useable Runways

Example: Approach Chart States

350 Hat and suggested Vis 1-1/2 vis (due to mountains)

Normal Alternate limits are now 700Hat and 3vis.
PROB limits are 400 Hat and 1-1/2vis

So why is it different because they use the word PROB?

If you have less than a 200 Hat or 1/2 Vis on a Standard ILS you have have to use a T/O Alt for departing this runway.

flyinhigh · Post by **flyinhigh** » Tue Dec 06, 2005 5:21 pm

BLZD1- damn you beat me to it. I agree, if there is no vis requirement than when you are determining you alternate why do we have to look at the 800-2, 400-1 etc.

My Question is though, you can use this do you really want to though?

My theory, and common sense is, I personally won't plan to go there if it is going to JUST make the requirements. I want to have flight planned for a spot that I know is going to be a sure thing, now once i'm in the air I will keep an eye on whats going on and if it'll work out that I can go there hey great, I'm sure that everyone else here is that way to though.
anyway cheers

BLZD1 · Post by **BLZD1** » Tue Dec 06, 2005 5:22 pm

Grey Area

CAR 602.123 States you must use both HAT and Visibility to calculate all Alternate numbers.

Alternate Aerodrome Weather Minima

602.123 No pilot-in-command of an aircraft shall include an alternate aerodrome in an IFR flight plan or IFR flight itinerary unless available weather information indicates that the ceiling and visibility at the alternate aerodrome will, at the expected time of arrival, be at or above the alternate aerodrome weather minima specified in the Canada Air Pilot.
Personally I would not use it as an alternate if it was legal. But I would use it as a diversion if I had a good alternate and bags of fuel.

Example: Departing Toronto to Halifax.

Halifax is a 1/8 of a mile in fog. Moncton was 3/4 mile in fog. Fredericton is Cavok.
Our company does not have any gate agents in Fredericton.

So our company would file Toronto to Halifax diversion to Moncton if could not land in Halifax. Even if Moncton does not meet Alternate limits then fly to Fredericton as our Alternate. It alot of fuel to carry but it is safe and legal!

snag · Post by **snag** » Tue Dec 06, 2005 5:24 pm

OK...For all you IFR newbs.

Summary of RAC 3.14 in the AIP (feel free to look it up):

Outlines the use of forecasts to determine suitable alternates.

If the weather is BECMG:

-If forecast to improve, use the weather before the BECMG period.
-If forecast to get worse, use the weather in the BECMG period.
(ie. worst case scenario)
-This weather can not be below ALTERNATE minima.

If the weather is TEMPO:

-This weather can not be below ALTERNATE minima.

If the weather is PROB 30/40 etc.:

-This weather can not be below the LANDING minima.

THEREFORE, since the landing minima is based on DH/MDA ONLY, It is ok to use this airport as an alternate.

Go Guns · Post by **Go Guns** » Tue Dec 06, 2005 5:39 pm

Wow, lots of people looking this up.

marktheone · Post by **marktheone** » Tue Dec 06, 2005 6:03 pm

Nope, no go for alternate, assuming 1 ILS you need 600-1. 1/4SM regardless of the ceiling is not the required 1SM.

BLZD1 · Post by **BLZD1** » Tue Dec 06, 2005 6:15 pm

Snag,

You are quoting Landing Limits not Alternate Limits. Landing Alternate limits ENROUTE are approach ban / MDA/ DH limited. For planning / dispatch purposes you must use HAT and Visibility as per the CARs 602 stated above for all alternates. Only difference with PROB is you use landing limits (HAT/ Vis) with no add ons.

What you are saying is I can have a PROB TAF 1/8 of a mile vis and a 200AGL vertical vis and this airport qualifies as an alternate. But if I depart in 1/8 vis and vertical vis 200AGL I need a T/O Alternate because I may not be able to return and Land.

You need 200AGL - 1/2 PROB to use it as an alternate!

BTD · Post by **BTD** » Tue Dec 06, 2005 6:17 pm

You don't require the 600-1 (it is actually 600-2)based on a probability. Its only the landing minima based on the approach plate itself. 600-2, 800-2 shouldn't even come into the argument for a probability.

Snag listed it beautifully.

If the weather is BECMG: ALTERNATE minima.
If the weather is TEMPO: ALTERNATE minima.
If the weather is PROB 30/40 etc.: LANDING minima. Landing minima only includes DH's MDA's (not vis)

2low · Post by **2low** » Tue Dec 06, 2005 6:18 pm

As long as you work for Navair, it doesn't matter!

Slayer · Post by **Slayer** » Tue Dec 06, 2005 7:57 pm

Although these type of Q's are seldom black and white this one is. Altiplano and snag nailed it. If I had no other useable airports in the vicinity I may find my inherent SPADAM convincing me not to though. (SPADAM= severe pain and death avoidance mechanism)