IMC vs. VMC

[SkyHog]

Ok - this is one of those questions that I've always had, but forgot the question whenever I was around anyone that could answer. It just came back to me in the shower.

On an IFR flight plan, in VMC, the pilot is responsible for See and Avoid. On an IFR flight plan in IMC, ATC is responsible for separation. How can anyone really know if you are IMC or VMC?

 

[Maverick]

There have been times while in IMC I was advised by ATC of traffic at such and such. In those cases my reply was 03V is IMC. Other than you or recent pilot reports in your vicinity telling them what the conditions are, how could they know. Of course you would know and I would assume you would keep an eye out for traffic when able.

Jeannie

 

[CFIse]

Ok - this is one of those questions that I've always had, but forgot the question whenever I was around anyone that could answer. It just came back to me in the shower.

On an IFR flight plan, in VMC, the pilot is responsible for See and Avoid. On an IFR flight plan in IMC, ATC is responsible for separation. How can anyone really know if you are IMC or VMC?

They don't care - ATC is only providing separation between you and other IFR traffic and they provide that regardless of if you are in VMC or IMC.

If you're in IMC the assumption is that there is no VFR traffic out there so the separation services being provided will be sufficient. If happens not to be true then you're just using the "big sky" theory of separation and ATC will be of no help to you.

 

[Lance F]

One thing that surprises me is the number of times when in solid IMC I get a report from ATC advising of VFR traffic. I know there's no way they can be legal VFR. All you can do is say "In IMC; no contact." If it seems like they're getting close, I guess I'd ask for vectors.

 

[Dave Siciliano]

I related a story 'bout a year ago about being IMC and having unreported traffic pass under me between clouds. Called Chicago center and their reply was, "that's not good"!!

So when IMC, Center is keeping you separated from other IFR traffic. If there is a rougue aircraft out there; hopefully, the big sky theory will assist ya. If in Class A airspace, you're probably in pretty good shape even VMC.

Best,

Dave

 

[spiderweb]

Tell them your are in IMC.

 

[SkyHog]

Tell them your are in IMC.

I just can't imagine this to be the only good answer. I try to avoid using the "big sky theory" as much as possible. It seems so unsafe to me to have the thought of a person flying VFR in the clouds, and there not being any responsibility of ATC to inform me, because he assumed I was in VMC as well...

 

[roncachamp]

Ok - this is one of those questions that I've always had, but forgot the question whenever I was around anyone that could answer. It just came back to me in the shower.

On an IFR flight plan, in VMC, the pilot is responsible for See and Avoid. On an IFR flight plan in IMC, ATC is responsible for separation. How can anyone really know if you are IMC or VMC?

On an IFR flight plan ATC provides separation from other IFR aircraft, doesn't matter if you're IMC or VMC.

 

[roncachamp]

I just can't imagine this to be the only good answer. I try to avoid using the "big sky theory" as much as possible. It seems so unsafe to me to have the thought of a person flying VFR in the clouds, and there not being any responsibility of ATC to inform me, because he assumed I was in VMC as well...

Nobody flies VFR in the clouds. If they're in the clouds they are not operating in accordance with Visual Flight Rules.

 

[mantakos]

The way the system works (outside of Class Bravo) is that ATC provides separation between IFR and IFR. ATC does not provide separation between VFR and IFR, nor between VFR and VFR, though they may provide callouts on a workload permitting basis. ATC doesn't need to know whether you're in IMC or not, they provide the same service regardless (though if you're in the clear, ATC may rely on pilots to maintain visual separation, if they acknowledge that they see the traffic).

_Pilots_ provide separation between VFR and VFR and between VFR and IFR. Clearly, this is only possible when the two planes are able to see each other, and thus is not possible inside a cloud. But VFR aircraft aren't supposed to be inside clouds, so this isn't supposed to be a problem. It's also challenging for pilots to maintain separation when an IFR plane busts out of a cloud into the clear, where VFR planes might be, which is why we have VFR cloud distance minimums.

This system breaks down when VFR aircraft violate the VFR minimums, and either fly too close to clouds or else fly in them. The best we get in this case is ATC's "best effort, workload permitting" traffic advisories.

As an IFR pilot, you are responsible for keeping an eye out the window, even when you're in IMC, to ensure that you continue to be in IMC. When you can see out the window, you're responsible for looking out for traffic.
-harry

 

[roncachamp]

The way the system works (outside of Class Bravo) is that ATC provides separation between IFR and IFR. ATC does not provide separation between VFR and IFR, nor between VFR and VFR, though they may provide callouts on a workload permitting basis.

ATC provides separation between VFR and IFR in Class C airspace.

 

[SkyHog]

On an IFR flight plan ATC provides separation from other IFR aircraft, doesn't matter if you're IMC or VMC.

How do they know you're in IMC?

edit: Because I'm pretty sure I remember seeing that ATC only separates IFR from IFR when in IMC, and pilots are responsible regardless if in VMC.

 

[EdFred]

Nobody LEGALLY flies VFR in the clouds. If they're in the clouds they are not operating in accordance with Visual Flight Rules.

Fixed for truth.

 

[roncachamp]

How do they know you're in IMC?

You'd have to tell them, but the separation rules do not change with the weather.

edit: Because I'm pretty sure I remember seeing that ATC only separates IFR from IFR when in IMC, and pilots are responsible regardless if in VMC.

You don't remember seeing that, you just imagined it.

 

[roncachamp]

Fixed for truth.

It was true as it was.

 

[flyingcheesehead]

edit: Because I'm pretty sure I remember seeing that ATC only separates IFR from IFR when in IMC, and pilots are responsible regardless if in VMC.

ATC separates IFR from IFR - But when they're VMC, the responsibility includes the pilots. That doesn't mean that ATC won't provide IFR-IFR separation when you're in VMC, it just means that if you smack someone, it's gonna be your fault. Not like that really matters once you splatter.

 

[poadeleted20]

It was true as it was.

If you're in the clouds, you are by definition operating under IFR; the only question is whether you're doing so legally. The exact reg you're violating depends on the situation (flight conditions, airspace, etc), and they have the option of charging you of violating either or both the VFR and/or the IFR rules. Beyond that, y'all can whip each other all you want.

 

[roncachamp]

If you're in the clouds, you are by definition operating under IFR; the only question is whether you're doing so legally. The exact reg you're violating depends on the situation (flight conditions, airspace, etc), and they have the option of charging you of violating either or both the VFR and/or the IFR rules. Beyond that, y'all can whip each other all you want.

Where can that definition be found?

 

[roncachamp]

ATC separates IFR from IFR - But when they're VMC, "responsibility" shifts to the pilots. That doesn't mean that ATC won't provide IFR-IFR separation when you're in VMC, it just means that if you smack someone, it's gonna be your fault. Not like that really matters once you splatter.

ATC responsibility for separation between IFR aircraft shifts not one bit between IMC and VMC.

 

[flyingcheesehead]

ATC responsibility for separation between IFR aircraft shifts not one bit between IMC and VMC.

Agreed - But when in VMC, *both* ATC and the pilots are responsible.

Edited the other post to make that a bit more clear.

 

[Ted]

If you're in the clouds, you are by definition operating under IFR; the only question is whether you're doing so legally. The exact reg you're violating depends on the situation (flight conditions, airspace, etc), and they have the option of charging you of violating either or both the VFR and/or the IFR rules. Beyond that, y'all can whip each other all you want.

I'm curious - how exactly would they prove that you were operating in IMC? I've had times when I've taken off into what was being reported as OVC015, found a nice hole to climb up through a few miles away to 8500 to get on top, and then got going. All with completely legal cloud clearances. From the controller's perspective, he sees a dot squawking 1200 until I get to a point to call for flight following, but the local METAR says I shouldn't be able to do what I'm doing. Even on days when Williamsport is reporting, say, OVC001, that can be over one side of the airport, and actually I could get out VFR the other way.

Unless I decided to sign a confession saying I illegally flew through IMC (regardless of whether I did or not), what would they violate me on? If I had a witness in the plane with me who confirmed that we did not fly through IMC, then what? Word against what?

 

[Dr. O]

I have a couple of times had the experience of being IFR in broken layers and having an unreported aircraft pass a few hundred feet underneath me, just flickering in and out of the holes in the layer...
Call ATC and ask about aircraft in my vicinity and get a negative report )

denny-o

 

[Rob Schaffer]

On our recent trip to / from Ohio, Gary M and I were VFR on the way home at 7500, wispy and overcast layer above us being reported at 8000 - 8500. We were notified by ATC of traffic 12 O'clock Westbound at 8000. He responded he was IMC, we were immediately told to maintain 7500 or below. About 30 seconds later,... "6708R, traffic no factor" and he relayed the same to the westbound traffic.

Then, about 45 minutes later getting closer to PA and now down at 5500 due to weather, We were told about traffic 4 miles at our 3 o'clock position, same altitude. Took us a while to find him, but we had to decend anyway to divert around some nasty looking clouds that were in our path and altitude. So we left 5500 for 3500. The controller asked us a few times for his location, and once we spotted him above us at 2 o'clock we reported him in sight. Then the controller asked us to estimate his altitude from us as about 1500-2000 above. Seemed to us that he wasn't talking to ATC, but we have no idea where he went or maintained VFR, as we were down below the deck that was building ahead of us and lost sight of him. Below is a photo of what we were going under/around at the time. I took this while we were on our decent.

 

[roncachamp]

I'm curious - how exactly would they prove that you were operating in IMC? I've had times when I've taken off into what was being reported as OVC015, found a nice hole to climb up through a few miles away to 8500 to get on top, and then got going. All with completely legal cloud clearances.

How do you know you had completely legal cloud clearances? Not saying you didn't, but how do you know you're, for example, 2200' laterally from a cloud and not 1800' from it?

From the controller's perspective, he sees a dot squawking 1200 until I get to a point to call for flight following, but the local METAR says I shouldn't be able to do what I'm doing. Even on days when Williamsport is reporting, say, OVC001, that can be over one side of the airport, and actually I could get out VFR the other way.

Departing Williamsport Regional? KIPT has a surface area, if the reported weather is 100' overcast you can't get in or out under VFR.

 

[EdFred]

How do you know you had completely legal cloud clearances? Not saying you didn't, but how do you know you're, for example, 2200' laterally from a cloud and not 1800' from it?



Departing Williamsport Regional? KIPT has a surface area, if the reported weather is 100' overcast you can't get in or out under VFR.

I'm sure that if the METAR says 10SM (or even 2SM) OVC001 I am sure there's something special he could do to depart legally without being IFR.

 

[roncachamp]

What if he is in a helicopter?

Nothing changes with a helicopter. Helicopters have lower VFR visibility and cloud clearance requirements than airplanes in Class G airspace within 1200' of the surface. No difference in controlled airspace.

 

[poadeleted20]

I'm curious - how exactly would they prove that you were operating in IMC?

Reported weather, witness statements, ATC tapes, etc. Check the NTSB Opinions and Orders for violations of 91.155 and 91.173, although you'll note that pretty much all of them involve flight near airports, where evidence is easier to develop.

 

[EdFred]

Nothing changes with a helicopter. Helicopters have lower VFR visibility and cloud clearance requirements than airplanes in Class G airspace within 1200' of the surface. No difference in controlled airspace.

Might want to read what I actually posted.

 

[roncachamp]

Might want to read what I actually posted.

Ah, I responded to your original post, I see now that you edited that message.

Yes, he could have requested Special VFR, but his statement was, "Even on days when Williamsport is reporting, say, OVC001, that can be over one side of the airport, and actually I could get out VFR the other way." Assuming he's departing KIPT his statement is incorrect.

 

[EdFred]

Ah, I responded to your original post, I see now that you edited that message.

Yes, he could have requested Special VFR, but his statement was, "Even on days when Williamsport is reporting, say, OVC001, that can be over one side of the airport, and actually I could get out VFR the other way." Assuming he's departing KIPT his statement is incorrect.

I look at SVFR as a square, and VFR as a rectangle.

 

[roncachamp]

I look at SVFR as a square, and VFR as a rectangle.

I agree with you completely, VFR and SVFR are not the same.

 

[EdFred]

I agree with you completely, VFR and SVFR are not the same.

But in the daytime they aren't so different either.

In regards to clouds and visibility, all you are doing is applying Class G below 1200' daytime VFR requirements to controlled surface areas.

Class G day, below 1200: 1sm, clear of clouds
SVFR : 1sm, clear of clouds.

Look pretty similar to me. Just like all sqaures are rectangles. I can make a Venn Diagram for you if it helps.

 

[poadeleted20]

Keep in mind that SVFR aircraft are being procedurally separated from IFR traffic. Regular VFR aircraft aren't. Thus, while is may seem somewhat similar to the pilot, it's a big difference for the controllers involved.

 

[Ted]

How do you know you had completely legal cloud clearances? Not saying you didn't, but how do you know you're, for example, 2200' laterally from a cloud and not 1800' from it?

The same as anyone else, which is a whole lot better than the controllers.

Departing Williamsport Regional? KIPT has a surface area, if the reported weather is 100' overcast you can't get in or out under VFR.

My point was worded poorly. You can have an inaccurate METAR or one that doesn't tell the whole story in the least. I have rarely seen a weather observation that actually tells me what I'm going to experience when flying into or out of the airport. Best it does is give me some vague idea. If it's reporting P6SM SKC then it's probably alright, but I've had some pretty extreme variations both directions.

Reported weather, witness statements, ATC tapes, etc. Check the NTSB Opinions and Orders for violations of 91.155 and 91.173, although you'll note that pretty much all of them involve flight near airports, where evidence is easier to develop.

This sounds to me like "Because they feel like it." I'm not seeing how they can come up with anything that ought to reasonably hold up. Weather stations are wrong, witnesses outside of the plane really can't have much of an idea, unless it's some other plane who is at the same position and same altitude while being in IMC, or alternately is in VMC and sees you popping out of a cloud.

I wasn't suggesting that people should break the rule, just wondering how it would be enforced. Seems from what you say like most of it comes down to pilots typically follow the rules as they're written in this case, which is fine by me, or the FAA will bust you if they feel like it, which is not.

Question has been answered to my satisfaction, thank you.

 

[roncachamp]

But in the daytime they aren't so different either.

In regards to clouds and visibility, all you are doing is applying Class G below 1200' daytime VFR requirements to controlled surface areas.

Class G day, below 1200: 1sm, clear of clouds
SVFR : 1sm, clear of clouds.

Look pretty similar to me. Just like all sqaures are rectangles.

You're not seeing the whole picture. Half the time an airplane and pilot must be capable of operating IFR in order to operate under SVFR. A SVFR operation must be separated from IFR and other SVFR operations all of the time. SVFR looks pretty similar to IFR to me.

I can make a Venn Diagram for you if it helps.

Cool! Do it.

 

[EdFred]

You're not seeing the whole picture. Half the time an airplane and pilot must be capable of operating IFR in order to operate under SVFR. A SVFR operation must be separated from IFR and other SVFR operations all of the time. SVFR looks pretty similar to IFR to me.

Cool! Do it.

Half the time during the day? When would that be? Because I'm pretty sure I started my post you replied to with "But in the daytime..." and I also qualified it with "in regards to cloud and visibility..." because I know on the controller side of things he has to provide separation.

 

[roncachamp]

The same as anyone else, which is a whole lot better than the controllers.

Well, how does anyone else do it?

My point was worded poorly. You can have an inaccurate METAR or one that doesn't tell the whole story in the least.

Yes, but an inaccurate observation or one that doesn't tell the whole story in the least is still binding.

I have rarely seen a weather observation that actually tells me what I'm going to experience when flying into or out of the airport. Best it does is give me some vague idea. If it's reporting P6SM SKC then it's probably alright, but I've had some pretty extreme variations both directions.

I don't think you'll see that in an observation.

 

[roncachamp]

Half the time during the day?

No, half of all the time.

When would that be? Because I'm pretty sure I started my post you replied to with "But in the daytime..." and I also qualified it with "in regards to cloud and visibility..." because I know on the controller side of things he has to provide separation.

Yes, as I said you were not looking at the whole picture.

 

[EdFred]

No, half of all the time.

Yes, as I said you were not looking at the whole picture.

I qualified it specifically. This is the same thing as me talking about squares, and you chiming in with how rectangles, trapezoids, rhombuses and other assorted 4 sided plane figures aren't perfectly symmetrical. I wasn't talking about night time operations or controller workload, I was specifically and only talking about daytime operations and cloud clearance requirements.

 

[roncachamp]

I qualified it specifically. This is the same thing as me talking about squares, and you chiming in with how rectangles, trapezoids, rhombuses and other assorted 4 sided plane figures aren't perfectly symmetrical. I wasn't talking about night time operations or controller workload, I was specifically and only talking about daytime operations and cloud clearance requirements.

Yes, as I said, again, you were not looking at the whole picture.

How's that Venn Diagram coming along?