Local weather phenomenon? Question!

[Adiabatic]

With 1/2 mile departure mins can an a/c leave with this weather? With that remark at 1420? From what I understand the reported ground vis has to be at or above the minimum, regardless of RVR. Is that 1/2 to 1/4sm a "local phenomenon"
Seems the smoke was around for a few hours....
Flight aware tells me interesting things

Thanks!!

CYHY 042000Z 12010KT 3/8SM FU VV010 27/12 A2995 RMK FU8 SLP146

CYHY 041913Z 12010KT 3/8SM FU OVC230 RMK FU6CI0

CYHY 041900Z 12011G17KT 1/2SM FU OVC230 26/12 A2997 RMK FU6CC0 VIS OCNL 3/8 SM SLP153

CYHY 041800Z 13009KT 3/8SM FU OVC230 24/12 A2999 RMK FU6CC0 SLP161

CYHY 041700Z CCA 14006KT 3/8SM FU OVC230 21/13 A3001 RMK FU6CC0 SLP168

CYHY 041600Z 10004KT 3/8SM FU OVC230 18/12 A3002 RMK FU6CC0 SLP169

CYHY 041500Z 14003KT 3/8SM FU OVC230 17/11 A3002 RMK FU6CC0 SLP171

CYHY 041420Z 10005KT 1/4SM FU OVC230 RMK FU6CC0 VIS VRB 1/2 - 1/4SM

CYHY 041400Z 10004KT 1/4SM FU VV009 13/10 A3002 RMK FU8 SLP171

CYHY 041300Z 14004KT 3/8SM FU VV009 13/10 A3002 RMK FU8 SLP171

CYHY 041200Z 15003KT 3/8SM FG FU VV009 13/10 A3002 RMK FU8 SLP171

CYHY 041100Z 12003KT 3/8SM FG FU VV009 13/10 A3003 RMK FU8 SLP172

CYHY 041000Z 00000KT 5/8SM FU VV009 14/11 A3002 RMK FU8 SLP171

CYHY 040900Z 18002KT 5/8SM FU VV009 13/11 A3002 RMK FU8 VIS 11/2 S SLP170

CYHY 040800Z 00000KT 1/2SM FU VV010 14/11 A3002 RMK FU8 VIS 1 1/2M S CIG EST DUE NO HELIUM SLP168

[Big Pistons Forever]

Assuming no RVR, unless the METAR visibility field says 1/2 mile or greater you can not go full stop. What is in the remarks is irrelevant except that it gives one hope that the vis will improve.

In these situations sometimes you have to hang out in the cockpit, ready to start and then jump on the first good enough METAR. The trick is to takeoff before the next METAR reducing the vis is issued, like the 13 minute window between 1900 and 1913 METAR's. If you were rolling at 1913 you were golden , at 1914 too bad so sad

I should add that true low vis takeoffs are not a great idea for newbie IFR or pilots that are not in practice.....

[Adiabatic]

Thanks! All understood. Yeah, new IFR pilots are expected to know everything about an airplane and IFR. It's nice to have a mentor step in and guide them and show them the rope and teach them all that is correct in the world right?

[eh3fifty]

What is in the remarks is irrelevant except that it gives one hope that the vis will improve.

I disagree.

If visibility is reported in the remarks section that indicates that there is a fluctuating visibility. If visibility is fluctuating it will show the average vis in the main section with the varying visibility values in the remarks - you need to take that into account.

For example, a visibility that is fluctuating between 3/8 and 3/4 would normally be shown as this:

CYHY 041420Z 10005KT 1/2 SM FU OVC230 RMK FU6CC0 VIS VRB 3/8 - 3/4SM

It appears that you have 1/2 SM for takeoff but you don't... using the lowest value (as there is no allowance for the takeoff ground visibility to be fluctuating), the takeoff visibility is 3/8 SM. You cannot takeoff.

As a note: tower observed visibility is ground visibility (as per CAR 101.01). It is only for the purposes of Aerodrome Operating Visibility (AOV) - which applies to landing and taxiing operations - that tower observed visibility does not take precedence over reported ground visibility (METAR, AWOS, etc.) Therefore, for takeoff visibility, the tower observed visibility is treated as a ground visibility. If the METAR says vis is varying between 3/8 and 3/4 SM and you ask the tower right before takeoff what their visibility is and they say 1/2 SM, then you're legal to takeoff.

A simplified takeoff visibility rule I came up with is this: "Takeoff visibility is the highest value of either the lowest RVR, or the lowest of a reported ground visibility; if neither are available it is assessed by the PIC."

[Big Pistons Forever]

I disagree with eh350's disagreement

A METAR, by definition is the visibility at the time of the report . Since the visibility is only measured once how can fluctuations exists, since those fluctuations have to occur over some time frame ?

The remarks column allows the observer to put additional information that could be of use to a pilot in the opinion of the observer. However it is just that additional information, the visibility field in the METAR is a legally required field with strict rules on how it is to be reported. It is that field which is intended to be used in order to decide whether conditions exist that will allow a takeoff that meets the requirements of the CAR's.

[AOW]

A range of visibilities listed in a metar remarks doesn't imply fluctuating vis, but rather that the vis in some directions is less, while it is more in others. The main text of the metar lists the " prevailing vis", and my interpretation is that if it is within limits, we're good to go.

[eh3fifty]

Since the visibility is only measured once how can fluctuations exists, since those fluctuations have to occur over some time frame ?

Yes, the fluctuations do happen over a short time period in which the observer is taking the observation.

However it is just that additional information, the visibility field in the METAR is a legally required field with strict rules on how it is to be reported. It is that field which is intended to be used in order to decide whether conditions exist that will allow a takeoff that meets the requirements of the CAR's.

No. The regulations specifically mention varying visibility. And varying visibility is reported in the remarks section. Everything in a METAR is a valid observation. Just because something is in the remarks section doesn't mean that it's invalid or not applicable. It seems other people also tend to ignore the remarks section for the ATIS as well. You still need to listen to that! They don't put that in there just for fun.

A range of visibilities listed in a metar remarks doesn't imply fluctuating vis

Yes, it does.

This is right from MANOBS paragraph 2.5:

When the visibility is observed to be fluctuating rapidly and increasing and decreasing from
a mean value by 1/4 or more of the mean value, the visibility is said to be “variable.” Use the
mean (average) of all observed values as the prevailing visibility.

Example: If the observed visibility fluctuates rapidly between 3/4 mi. and 1 1/4 mi., the
prevailing visibility would be reported as 1 mi.. To report the variability, see 10.2.19.3,
“Visibility (Remarks).”

And 10.2.19.3 shows this:
http://i.imgur.com/2uLHKgu.jpg

In summary, the remarks section is used to indicate that the prevailing visibility is varying.

You can download the MANOBS for free from the Environment Canada website.

[Big Pistons Forever]

A range of visibilities listed in a metar remarks doesn't imply fluctuating vis

Yes, it does.

This is right from MANOBS paragraph 2.5:

When the visibility is observed to be fluctuating rapidly and increasing and decreasing from
a mean value by 1/4 or more of the mean value, the visibility is said to be “variable.” Use the
mean (average) of all observed values as the prevailing visibility.

Example: If the observed visibility fluctuates rapidly between 3/4 mi. and 1 1/4 mi., the
prevailing visibility would be reported as 1 mi.. To report the variability, see 10.2.19.3,
“Visibility (Remarks).”

And 10.2.19.3 shows this:
http://i.imgur.com/2uLHKgu.jpg

In summary, the remarks section is used to indicate that the prevailing visibility is varying.

You can download the MANOBS for free from the Environment Canada website.

Interesting as I always thought and the AIM also reports what AOW said, that is visibility reports in the remarks column refers to sectors around the airport that may have different visibility.

However back to the main question which is can you takeoff when you have a METAR prevailing visibility (ie what is shown in the main field) of less than 1/2 miles say 3/8 but a remarks column which says vis 1/4 to 1/2 ?

So when in doubt I go to the CAR's

602.126 (1) No pilot-in-command of an aircraft shall conduct a take-off if the take-off visibility, as determined in accordance with subsection (2), is below the minimum take-off visibility specified in

(a) the air operator certificate where the aircraft is operated in accordance with Part VII;
(b) a special authorization issued under subsection 604.05(2); or
(c) the Canada Air Pilot in any case other than a case described in paragraph (a) or (b).

(2) For the purposes of subsection (1), the take-off visibility is

(a) the RVR of the runway, if the RVR is reported to be at or above the minimum take-off visibility specified in a document or the manual referred to in subsection (1);
(b) the ground visibility of the aerodrome for the runway, if the RVR

(i) is reported to be less than the minimum take-off visibility specified in a document or the manual referred to in subsection (1),
(ii) is reported to vary between distances less than and greater than the minimum take-off visibility specified in the Canada Air Pilot or a certificate referred to in subsection (1), or
(iii) is not reported; or

(c) the runway visibility as observed by the pilot-in-command, if
(i) the RVR is not reported, and
(ii) the ground visibility of the aerodrome is not reported.

Not that the CAR's specifies that the variable visibility exception is specific to only RVR information and that there is no prevision in the CAR's to account for variable visibility in a METAR with no comparison RVR information.

Since Hay River does not have a RVR system the only time a takeoff would be legal is when the METAR prevailing visibity ( ie the main field in the text) was 1/2 mile or greater (assuming a low vis op spec was not held)

[eh3fifty]

a METAR prevailing visibility (ie what is shown in the main field)

When the prevailing visibility in the main section is fluctuating, the fluctuations are indicated in the remarks section. This is addressed in MANOBS. I also called a weather briefer at 866-WX-BRIEF and he said the same thing as MANOBS and actually referenced the MANOBS for me. As for the AIM not agreeing with MANOBS, it is actually talking about something different than varying visibility and I will explain that at the end.



Varying visibility means that the prevailing visibility value ("the maximum visibility value common to sectors comprising one-half or more of the horizon circle") is varying. It is not talking about a lone sector of the horizon circle.

To address the AIM quote:

In the MET section it says: "Prevailing visibility—The prevailing visibility is reported in statute miles and fractions. There is no maximum visibility value reported. Lower sector visibilities which are half or less of the prevailing visibility are reported as remarks at the end of the report."

This is addressed in MANOBS 16.3.6.2:



These are entirely different things. The AIM and MANOBS do not conflict. The AIM is talking about visibilities that are "half or less" of the prevailing visiblity - that is addressed in 16.3.6.2 and they're indicated in the METAR with the format "VIS S 6".

The AIM does not address varying visibility - MANOBS 2.5 addresses that. It also says that 1/4 SM difference from the mean value is enough to consider the prevailing visibility to be varying. So if the visibility is varying 1/2 SM total, it is varying 1/4 SM from the mean. Here is an example METAR that includes both a varying visibility and a lower sector visibility, which the AIM talks about:

CYHY 041420Z 10005KT 2 SM FU OVC230 RMK FU6CC0 VIS VRB 1 3/4 - 2 1/4SM VIS S 1 SLP980

there is no prevision in the CAR's to account for variable visibility in a METAR with no comparison RVR information.

Correct. You must, in that case, use the lowest visibility value. If it is fluctuating then you use the lowest value. When you are dealing with approach bans there is an exception for ground visibility to be fluctuating. That is not the case for takeoffs. You can, however, use the lowest of any ground visibility for takeoff [EDIT: including AWOS. CYNE has a METAR and AWOS so you could be banned from takeoff by the METAR but the AWOS' up-to-the-minute visibility could indicate you have 1/2 SM and, if so, you'd be legal to takeoff.]. If the METAR reported on the hour (36 min old) is reporting 3/8 SM and the tower says that he's reporting visibility as 1/2 SM then you can takeoff.

[StratusSmoke]

There is no definition of "rapidly" in MANOBS. Observers are outside for like two minutes max (usually a lot less during inclement weather) for the observation and we use variable so we don't have to continuously issue SPECIs. Everyone has seen how an AWOS can issue like 20 SPECIs in half an hour...it's annoying, so we use variable. Back in the old days we also used to call the ceilings at a thousand with variable 8-12 to bypass the SVFR. That and calling it "-BKN" moved the traffic expeditiously.

As for the time of a SPECI....that is usually the time the event was observed, it will likely take several minutes for the observation to be entered and several more before it is available to anybody other than the observer. It is conceivable that an aircraft could depart illegally and not even know it.

[eh3fifty]

Observers are outside for like two minutes max (usually a lot less during inclement weather) for the observation and we use variable so we don't have to continuously issue SPECIs. Everyone has seen how an AWOS can issue like 20 SPECIs in half an hour...it's annoying, so we use variable.

So what you're describing is actually variable conditions. It makes sense then that it would be reported as variable visibility.

It is conceivable that an aircraft could depart illegally and not even know it.

I do not see how a competent pilot could depart illegally and not know it. The key words are competent and pilot. If you receive the current weather reports and one of them says you can takeoff, then you can legally takeoff. It doesn't matter if another report comes out after you takeoff with an observation time before your takeoff time that says it was below takeoff visibility - the visibility report available at the start of the takeoff roll indicated it was good for takeoff, therefore, it was legal to takeoff. The rules are designed with some common sense built in.

[StratusSmoke]

My bad....substitute "below limits" for "illegally". Although that is splitting a mighty fine hair IMO.

[Bede]

I have found that when the vis goes down, you taxi out to the runway, turn with your exhaust towards the transmissometers and power up. That usually gets the vis up just enough to get you out of there.

[AuxBatOn]

It is the visibility at take off time, not METAR time. Ask tower what the RVR is (or ground vis if no RVR) If it's greater than your minimum, you're good.

[Big Pistons Forever]

It is the visibility at take off time, not METAR time. Ask tower what the RVR is (or ground vis if no RVR) If it's greater than your minimum, you're good.

Tower reported vis can never overrule a below 2600 RVR and a below 1/2 mile METAR reported visibility at a civilian aerodrome.

[AuxBatOn]

Tower has a live RVR reading and tower can report ground vis. I'd be curious to see your reference...

[Big Pistons Forever]

Ask tower what the RVR is (or ground vis if no RVR) If it's greater than your minimum, you're good.

Aux

There is no way for the tower, or FSS, to report "ground vis". So unless there is an RVR which is not the case at the airport referenced by the OP, or most airports in Canada for that matter, there is no way for you to take off in the case of a METAR report of less than 1/2 mi visibility (assuming no OPSPEC). If the METAR was below 1/2, but the RVR was 2600 or better then yes you can off but this only applies to an RVR visibility as reported by the tower. RVR is not ground visibility and this was the point I was trying to make, although in retrospect I did not word my response very clearly.

[AuxBatOn]

So, if the METAR shows 1/4 SM but the vis is actually 2 SM (because METAR is old), you won't take off?

For the civi tower types, are you allowed to assess and report ground vis?

[Big Pistons Forever]

So, if the METAR shows 1/4 SM but the vis is actually 2 SM (because METAR is old), you won't take off?

Correct, I will have to wait for a SPECI to be issued showing the 2 miles.

[AuxBatOn]

Jesus lack of common sense... And lack of understanding of the rule... Because Tower, FSS or even a radio station manned by an operator can report visibility. From the CARs:

“ground visibility”, in respect of an aerodrome, means
the visibility at that aerodrome as contained in a weather
observation reported by
(a) an air traffic control unit,
(b) a flight service station,
(c) a community aerodrome radio station,
(d) an AWOS used by the Department of Transport,
the Department of National Defence or the Atmospheric Environment Service for the purpose of making
aviation weather observations, or
(e) a radio station that is ground-based and operated
by an air operator; (visibilité au sol)

They are qualified as observers (as per MANOBS) and have defined markers they use to define visibility (and I confirmed this with both mil and civy Tower types).

The rule is not meant to prevent people from taking off when they should but rather to prevent them from taking off when they shouldn't and provide different layer of safety while maintening some flexibility in its application.

[eh3fifty]

It is the visibility at take off time, not METAR time. Ask tower what the RVR is (or ground vis if no RVR) If it's greater than your minimum, you're good.

No, a METAR is a valid ground visibility. If the ground visibility changes a certain amount then a SPECI will be issued revising the ground visibility.

For takeoff, you need to use the lowest of any reported ground visibility. That means that you can use any ground visibility but you must take the lowest reported value. If the METAR reports ground vis as 1/2 SM and VIS VRB 3/8 to 5/8 then the ground visibility you need to use for takeoff is 3/8 SM. If the tower also reports that the visibility is 1/2 SM you may use that and legally takeoff.

Tower reported vis can never overrule a below 2600 RVR and a below 1/2 mile METAR reported visibility at a civilian aerodrome.

I will disagree. For the purposes of taxiing and landing, tower reported visibility is only advisory unless there is no other ground visibility reported; in that case tower visibility counts as ground visibility. For the purposes of takeoff, there is no such restriction on tower visibility and, therefore, it falls under the category of ground visibility. For takeoff, as long as there is one ground visibility whose lowest value is equal to or above your takeoff minima, you may legally takeoff - this is true even if the RVR is below takeoff minima.

If you have a reference stating what you said, I'd be happy to reconsider my view.

So, if the METAR shows 1/4 SM but the vis is actually 2 SM (because METAR is old), you won't take off?

That is unrealistic and wouldn't happen. A SPECI would be issued once the vis reached 1/2 SM. Reference for this is MANOBS 10.3.5.4.

You are correct that tower visibility does count and is a valid ground visibility for the purposes of takeoff.

[AuxBatOn]

No, a METAR is a valid ground visibility. If the ground visibility changes a certain amount then a SPECI will be issued revising the ground visibility.

For takeoff, you need to use the lowest of any reported ground visibility. That means that you can use any ground visibility but you must take the lowest reported value. If the METAR reports ground vis as 1/2 SM and VIS VRB 3/8 to 5/8 then the ground visibility you need to use for takeoff is 3/8 SM. If the tower also reports that the visibility is 1/2 SM you may use that and legally takeoff.

Never said a METAR isn't valid ground vis. However, if you have a more recent report from tower, this takes precedence (ie: METAR is from 1900Z tells you 1/4 SM but tower gives you a visibility of 1/2 SM at 1901Z) you are good to go. In fact, it is used all the time here by civilians.

That is unrealistic and wouldn't happen. A SPECI would be issued once the vis reached 1/2 SM. Reference for this is MANOBS 10.3.5.4.

Rapidly changing weather... The time it takes to get the SPECI in the system.... You know what I mean.. Unlikely but possible.

[eh3fifty]

Never said a METAR isn't valid ground vis. However, if you have a more recent report from tower, this takes precedence (ie: METAR is from 1900Z tells you 1/4 SM but tower gives you a visibility of 1/2 SM at 1901Z) you are good to go. In fact, it is used all the time here by civilians.

There is no precedence for a "recent" report. The airplane was legal to takeoff in that case, not because the tower report was more recent but, because a ground visibility report had a value of 1/2 SM or higher.

[AuxBatOn]

What if the METAR @ 19Z says 1/2 SM but when asked, tower reports 1/4SM visibility at 1915Z? Is this legal? I would say no, or at the very least that it doesn't meet the intent of the rule.

[Cat Driver]

How does any sane country get to the point where their rules are so convoluted that this large a group of pilots can not agree on what is legal and what is not?