IFR alternate

[canadianflygal]

So, I understand that even if a tempo is great, if the base TAF is below alternate minimums than the tempo does not supersede this. how about for PROB or BCMG? Im assuming the same goes for them as for the tempo? So pretty much, if the base taf is below normal limits then theres no point in even looking at the TEMPO,BCMG, or PROB???

Thanks a lot for the input

[swordfish]

If the wx is TEMPOrarily better than alternate limits, you cannot depend on it for the time of your arrival; therefore you can only use the place as an alternate if the rest of the TAF is at/above alternate limits for your ETA. The weather in the TEMPO period has to always be at/above the alternate minima to use the TAF for the whole period of the forecast. (i.e. you have to consider the worst weather you will encounter at your proposed ETA in the whole TAF, including the TEMPO period)

If PROBability is there, if the PROB wx is at or better than the landing minima (not the alternate minima normally required), you can use it as an alternate. If it's below the landing minima for the runway of intended use, you cannot use it (be sure to check the winds and NOTAM for that runway).

If BCMG is there: if the wx is improving, you can only use that wx forecast at the end of the BCMG period.
if the wx is forecast is deteriorating at that time, you must use the forecast at the beginning of the BCMG period.

p.s. it can be dangerous to use/rely on the PROB forecast for your planning; things change over the course of your flight; so does the facility status.
p.s. Remember that if standard minima can be applied (i.e. 800/2) this can 'slide' (900/1½, 1000/1)

[looproll]

So, I understand that even if a tempo is great, if the base TAF is below alternate minimums than the tempo does not supersede this. how about for PROB or BCMG?

You mean if the PROB period is within alternate mins? NO you can't use it in that case. But probs are usually for conditions that will be worse than the forecast period they are within, often something funky like fog or CBs.

BCMG? not during the becoming period but you can at the end of the BCMG time if it's within limits.

It's good to note that if the PROB condition is below alternate minimums, but at or above LANDING minimums for a usable IFR approach, it can be used. For instance if you're looking at a 400-1 alternate limit but the is a PROB30 for 200ft and 1/2 mile, as long as it's not below landing minimums you are legal.

Legal as safe are two different things though.

[Koizie1]

If a TEMPO is below alternate requirements for your ETA at alternate, then you cannot use that airport as your alternate. Simple.

If the TEMPO is the worst forecast, use that. If the base TAF is the worst forecast, use that.

If TEMPO and TAF are above the alternate minima, and there is a PROB, then the PROB must be above the landing minima (as given on the approach plate) for the runway of intended use. If not, then you can't use as your alternate. This has screwed me many times, not that I'm complaining.

Someone else covered BCMG above.

All of these requirements have to be met.

[Vortex_driver]

Here's another question,

regarding landing minimas for the Prob, does the advisory visibility stands as a minima ? for example, your minima is 300/1SM and the Prob is 400 feet and 3/4SM, would you be able to use it? Does the ops spec or airport visibility(for cases below 1/2SM comes into play to determine the minima...?

had this situation a while ago with my dispatch and I wasn't 100% sure...

[canadianflygal]

thanks for all of your replies!!

I dont think I worded the question properly though. I understand using the landing min. with PROB and using beginning of the period if supposed to deteriorate and vice versa if its supposed to get better for the BCMG periods. What Im not 100% sure of is this: if the overall base TAF is below minimums, then even if we have a tempo period that is above minimums we still can not use it. Now lets say that we have a TAF below mins with a BCMG that has wx well over minimums.. does the base TAF over rule the BCMG and PROB periods as it does the TEMPO? I understand that using common sense, you wouldnt base your whole alternate on a PROB or a chance of it BCMG better than minimums but by the books whats the rule with those two???

Thanks again

[BTD]

The BCMG becomes the base TAF at the end of the change period. Think of it like a FM that will change over usually 2 hrs.

If the weather in the TAF is below alt mins, but there is a BCMG period with good weather in the TAF, then at the end of the BCMG period you may use it as an alternate.

I altered the below to make it useful.

TAF CYSB 271938Z 2720/2808 16005KT P6SM BKN001 OVC030 TEMPO 2720/2802
BKN030
BECMG 2800/2802 VRB03KT P6SM OVC050
RMK NXT FCST BY 280200Z=

At 02z everything before the BECMG period is irrelevant. If you plan to get there after 02z you may use it as an alternate. OVC050 is now the base TAF from then on.

BTD

[swordfish]

for Vortex_Driver:

No the advisory visibility cannot be used in determination. This is issued by a person at the aerodrome, when you are inbound; you would not have this information available to you at the time of flight planning. "Tower observes...", "FSS observes...", "CARs operator observes...." - none of these can be used for flight planning or approach ban considerations. None of them overrules the heirachy laid out in CAP Gen.

In your example, you cannot use that airport as an alternate, because the required minima are 300/1, and with ¾ mile vis in the PROB period, you cannot use it - IF YOUR ETA IS IN THE PROB PERIOD.

No, the RVOP and LVOP of the airport play no part in this determination of alternate.

No, your Ops Spec is not considered in the determination of an alternate; it is based on the CAP-published minima. I don't know of any approaches that use lower than ½ SM (except where there are CAP II and III limits published).

These criteria you allude to are not used for in-flight operations; they are determined at the time of flight planning. Of course if the TAF for a possible alternate gets amended while you are enroute, you can change your alternate. You would the have to notify ATC of that. Alternate selection is based on TAFs, at your ETA, not actual weather.

All this stuff is found in CAP Gen, RAC 3.14, and CAR 602.123.

Again, I caution pilots against relying on PROBs. It is risky. You miss an approach at Peace River, your alternate is Grande Prairie, and the glide path goes down...you are in deep gaagaa. Make sure your alternate is secure! If you're looking at a PROB simply because it says 200/½, think seriously about whether you should be selecting that place as a secure alternate.

[swordfish]

if the overall base TAF is below minimums, then even if we have a TEMPO period that is above minimums we still can not use it.

Now lets say that we have a TAF below mins with a BCMG that has wx well over minimums.. does the base TAF over rule the BCMG and PROB periods as it does the TEMPO?

There are 3 issues here, that are not related:

First one: NO you can't use that place as an alternate, because the 'base" part of the TAF prohibits it, regardless of the fact that the TEMPO has better wx in it.

Second one: YES, you can use the place as an alternate, but not until at the END of the BCMG period, in your example.

Third one: If the weather in the PROB period is at or above LANDING limits for your forecast ETA, YES, you can use it as an alternate, but the wx in the "base" TAF all has to be above ALTERNATE limits - including what's in the TEMPO part. If there worse wx in the PROB, it does not prohibit using the place as an alternate, providing it's not below LANDING limits.

[swordfish]

Here are some examples for Timbuctu, NWT (TMBC2 has an ILS on Rwy 15, and you can use standard minima):

Note that I have omitted the date (28th) and reformatted the NavCan layout for ease of your reading & understanding:

You CANNOT use this one:

TAF TMBC2: issued 281145 for use 281200-282400:
16009KT P6SM OVC006
TEMPO 21-23 P6M BKN020
PROB30 18-21 ¾SM OVC003 BR DZ -RA
NEXT FCST 282345

You CAN use this one before 18z, and CAN after 22z:

TAF TMBC2: issued 281145 for use 281200-282400:
16009KT 2SM FEW002 SCT004 BKN008 OVC020
TEMPO 18-20 1½SM BKN008 BR DZ
PROB40 16-18 1SM OVC005
BCMG 20-22 P6M BKN008
NEXT FCST 282345

You CANNOT use this one until 22z:

TAF TMBC2: issued 281145 for use 281200-282400:
16009KT 1½SM FEW002 SCT 004 BKN008 OVC020
TEMPO 16-18 2SM BKN009 BR DZ
PROB40 14-16 1SM OVC002 BR DZ
BCMG 20-22 P6M BKN008
NEXT FCST 282345

You CAN use this one:

TAF TMBC2: issued 281145 for use 281200-282400:
16009KT 2SM FEW002 SCT004 BKN008 OVC020 BR
TEMPO 16-18 1½SM BKN009 BR DZ
PROB40 16-18 1SM OVC003 BR DZ
BCMG 20-22 1SM BKN010 -RA BR DZ
NEXT FCST 282345

You CANNOT use this one after 20z:

TAF TMBC2: issued 281145 for use 281200-282400:
16009KT 1½SM FEW002 SCT 004 BKN008 OVC020
TEMPO 16-18 2SM BKN009 BR DZ
PROB40 14-16 1SM OVC002 BR DZ
BCMG 20-24 P6M BKN006
NEXT FCST 282345

[matrix]

Here are some examples for Timbuctu, NWT (TMBC2 has an ILS on Rwy 15, and you can use standard minima):

Note that I have omitted the date (28th) and reformatted the NavCan layout for ease of your reading & understanding:

You CANNOT use this one:

TAF TMBC2: issued 281145 for use 281200-282400:
16009KT P6SM OVC006
TEMPO 21-23 P6M BKN020
PROB30 18-21 ¾SM OVC003 BR DZ -RA
NEXT FCST 282345

Why can't you use the above one? Assuming standard ILS alternate minima 600-2 and landing minima 200-1/2. This appears to be a legal altn for the entire TAF.

You CAN use this one before 18z, and CAN after 22z:

TAF TMBC2: issued 281145 for use 281200-282400:
16009KT 2SM FEW002 SCT004 BKN008 OVC020
TEMPO 18-20 1½SM BKN008 BR DZ
PROB40 16-18 1SM OVC005
BCMG 20-22 P6M BKN008
NEXT FCST 282345

The above example is a legal alternate for the entire TAF.

You CANNOT use this one until 22z:

TAF TMBC2: issued 281145 for use 281200-282400:
16009KT 1½SM FEW002 SCT004 BKN008 OVC020
TEMPO 16-18 2SM BKN009 BR DZ
PROB40 14-16 1SM OVC002 BR DZ
BCMG 20-22 P6M BKN008
NEXT FCST 282345

This one above is also legal for the entire TAF

You CANNOT use this one after 20z:

TAF TMBC2: issued 281145 for use 281200-282400:
16009KT 1½SM FEW002 SCT 004 BKN008 OVC020
TEMPO 16-18 2SM BKN009 BR DZ
PROB40 14-16 1SM OVC002 BR DZ
BCMG 20-24 P6M BKN006
NEXT FCST 282345

This one is also a legal altn for the entire TAF

[Vortex_driver]

Thanks Swordfish!

I guess my question was Is the Advisory visibility a minima for flight planning purposes... And the anwser is obviously yes because that's what we are using for the 2SM in the 800/2 rule!

Thanks

[square]

To answer the OP: No. If the TAF is below alternate minima you can't use it as an alternate. Pretty straight forward. Just cause you have a TEMPO that is above alt minima doesn't change that. TEMPO's are only supposed to be temporary changes for less than 50% of the TEMPO period. So a TEMPO period "P6SM SKC" obviously would not make a TAF of "OVC002 1 SM" a legal alternate. Just as a TAF of "P6SM SKC" is not a legal alternate if there's a TEMPO of "OVC002 1 SM."

TAF, TEMPO & BCMG must all meet alternate minima for your ETA. PROB has to meet landing minima.

[square]

The BCMG becomes the base TAF at the end of the change period. Think of it like a FM that will change over usually 2 hrs.

Not exactly true. A FM cancels all items of a previous TAF period. A BCMG only changes certain specified items of a TAF period. Lots of BCMG periods will just have the winds in there, so the rest of the previous period remains, unlike a FM change.

[aviator2010]

what i love about the cars is how strait forward ans simple they are

[200hr Wonder]

If the weather is that close to being at alternate minima, add a bag of gas and find a better alternate.

[x-wind]

Didn't read all past the first post but- why go with second hand information? Look it up.

Also, here is something you won't read- you don't have to go to your IFR alternate if you can't get into the destination. You need to have an IFR alternate because it's such a good flight planing idea they made it a regulation. If you've the petro you can give your "in the event of a missed approach" request for a clearance to a nearby airport that isn't your IFR alternate. Just don't put yourself in a bad situation.. meaning you should have the gas for that nearby airport + approach + missed and the IFR alternate + reserve requirements.

Again though... read the AIM and look this stuff up. It's handy to download the AIM in pdf. format and use the search or keyword function in your pdf. reader.

One more thing, for a calm wind day in Victoria, which has two ILSs, you cannot use the alternate minimum of for two or more precision approaches. The reason is- it's the same piece of asphalt, albeit separate ILSs on different ends. You need to separate pieces of real-estate. So said a couple of TCCA guys when I phoned from underneath my umbrella one afternoon.

Cheers,

"Everything should be made as simple as possible, but not simpler."

[swordfish]

Matrix:

Sorry...you are correct in your challenges: I was forgetting the ILS minima 600/2, and that DOES slide. Good catch!

[swordfish]

One more thing, for a calm wind day in Victoria, which has two ILSs, you cannot use the alternate minimum of for two or more precision approaches. The reason is- it's the same piece of asphalt, albeit separate ILSs on different ends. You need to separate pieces of real-estate. So said a couple of TCCA guys when I phoned from underneath my umbrella one afternoon.

Yes, I ran into the same issue with TC when I was at Buffalo Narrows. They seem to think that 2 ILSs on the same slab cannot be used (13/31 YWG). I guess their thinking is if there's a wind blowing, only 1 ILS is "usable".

My perspective is that if it's calm, you can use either one. Also, the regs simply say "2 usable precision approaches each providing straight-in minima to separate suitable runways". i.e. you can't plan to approach from the downwind ILS and circle for the into-wind runway. But I can't see why you cannot consider 13 and 31 as 2 separate runways.

Seems to me that the "suitability" of a runway would be gauged by what sort of downwind component you can tolerate as per the POH/AFM and your Ops Manual.

I suppose the issue is not only facility redundancy & weather (wind) contingency, but if one slab becomes unusable because of a disabled aircraft, then the other slab is available. Of course, this ignores the possibility of both runways being closed because it happened at the intersection....

[BTD]

The BCMG becomes the base TAF at the end of the change period. Think of it like a FM that will change over usually 2 hrs.

Not exactly true. A FM cancels all items of a previous TAF period. A BCMG only changes certain specified items of a TAF period. Lots of BCMG periods will just have the winds in there, so the rest of the previous period remains, unlike a FM change.

You are correct. I should watch my wording. I should have said, if there was a change in the BCMG period the same item before the change is now irrelevant.

In my example I changed everything after the BCMG period, so it still works.

BTD

[AuxBatOn]

Yes, I ran into the same issue with TC when I was at Buffalo Narrows. They seem to think that 2 ILSs on the same slab cannot be used (13/31 YWG). I guess their thinking is if there's a wind blowing, only 1 ILS is "usable".

Not quite. It's more because if someone fouls the runway or the runway becomes unusable, you put yourself in a corner by accepting lower alternate minima, which are just marginally above the actual approach minima and often below non-precision approach minima. We have 2 precision approach on the same runway in Bagotville, using different navaids (ILS/TACAN 29 and PAR 29) and yet, we cannot use alternate weather requirements for CYBG as 2 precision approaches.

Let's make an example. You file CYBG as an alternate and use the 2 precision approaches alternate minima, which gives you 400-1 as the minimum weather. The weather is forecasted to be... 400 and 1 the whole day. Great you think. You get to destination, realize that you won't get in, divert to you alternate. ATIS says the weather is 500 and 1 and calm winds. Great. You are on vectors and a Hornet needs to take a cable on 29. He takes the cable and fouls the runway for 30 minutes. The only other alternative for you would be a circling approach to 18 or 36. The minima is around 600' for that. Because you planned with the 2 precision approaches, you are now royally screwed, having only gas to hold for 15 minutes (assuming a jet) before shooting the approach.

We could make a similar scenario with YWG, making the ILS 36 U/S and some Sky North Navajo landing gear up on 31.

[x-wind]

Regarding two ILSs & the same stretch of pavement: AuxBatOn has it right, at least as I and the TCCA guys/gals see it.

Also, it was wrote: "In your example, you cannot use that airport as an alternate, because the required minima are 300/1, and with ¾ mile vis in the PROB period, you cannot use it - IF YOUR ETA IS IN THE PROB PERIOD."

I believe you're mistaken.

RAC 3.14 (d) "the forecasted PROB shall not be below the appropriate landing minimum for that aerodrome."

The term "landing minima" is significant.

RAC 9.19.3 Landing Minima : "CARs 602.128 specifies that landings are governed by published DH/MDAs." "Published landing visibilities associated with all instrument approach procedures are advisory only."

[swordfish]

Regarding two ILSs & the same stretch of pavement: AuxBatOn has it right, at least as I and the TCCA guys/gals see it.

Also, it was wrote: "In your example, you cannot use that airport as an alternate, because the required minima are 300/1, and with ¾ mile vis in the PROB period, you cannot use it - IF YOUR ETA IS IN THE PROB PERIOD."

I believe you're mistaken.

RAC 3.14 (d) "the forecasted PROB shall not be below the appropriate landing minimum for that aerodrome."

The minima quoted in her example required 300' and 1 sm. The PROB said it was going to be ¾. Therefore cannot be used if the ETA is in that PROB period.

However, I did screw up in some of my examples by forgetting the single ILS permits 600/2 (which slides) selection for alternate... caught by Matrix...

"Published landing visibilities associated with all instrument approach procedures are advisory only."

I think the jury is out on this. Where LVOP or RVOP procedures are published for an airport (and most ILS-equipped airports have them now) the vis does become limiting.

AuxBatOn:

The example you quote for CYBG uses 2 precision approaches for the same runway. The wording in CAP Gen is for 2 different runways. I simply consider 13 & 31 as being 2 different runways.

And Yes, I do concur with the disabled aircraft scenario. (However statistically unlikely it is...) And I only say that because we fly daily accepting some risks that are statistically improbable.

[AuxBatOn]

AuxBatOn:

The example you quote for CYBG uses 2 precision approaches for the same runway. The wording in CAP Gen is for 2 different runways. I simply consider 13 & 31 as being 2 different runways.

And Yes, I do concur with the disabled aircraft scenario. (However statistically unlikely it is...) And I only say that because we fly daily accepting some risks that are statistically improbable.

The disabled aircraft scenario is not that unlikely. It happens quite frequently that a runway will become unusable for any reason. There are some risks we accept. Is accepting lower alternate minima an acceptable risk when we can mitigate it otherwise?

As far as my understanding goes, Runway is defined as the piece of concrete (ie: Runway 18-36). TC does not provide any definition of Runway.

[Vortex_driver]

The landing minima definition is what got me confused initially... BUT when you think about it, when we calculate the 600/1 or 800/2 we are using a visibility which comes from the advisory visibility which becomes limiting...


Same goes for the PROB. We have to use the avisory visibility as a litiming factor FOR FLIGHT PLANNING PURPOSES.