IMC vs. VMC
Chad R. Speer
Hello everyone. If this thread gets long, feel free to reply only to
rec.aviation.ifr. No need to have three long threads going. (optimism
maybe?)
There has been an ongoing discussion in rec.aviation.ifr about the
definitions of IMC and VMC. The pilot/controller glossary mentions
"conditions ... equal to or better than specified minima" but gives no
reference to these minima. Some pilots believe IMC means you can't fly
by visual reference. The debate is endless.
Here's the question - does anyone really use these terms? If so, what do
they mean to you? Do you know of any references to VMC or IMC in the
FARs or AIM? How about anywhere else (advisory circulars, weather
manuals, etc.)?
I am going to follow through with this to the FAA and see if I can find
out a few things:
1. What do VMC and IMC *really* mean?
2. Is there any official FAA usage of the acronyms?
3. If the FAA does use them, is the usage consistent with the
definition in the P/CG?
4. If the FAA does not use them, why are they defined?
If anyone *knows* the answer to any of these questions, please post. It
just seems silly to have such vaguely defined terms in our vocabulary
when we are used to dealing with rather exact meanings. I'm serious
about following up with the FAA on this, so I want to gather all the
information I can now.
Chad Speer
PP-ASEL, ATCS
Andrew M. Sarangan
In article <34CCDF...@leatherneck.com>,
Chad R. Speer <sp...@leatherneck.com> wrote:
>
>1. What do VMC and IMC *really* mean?
>
>2. Is there any official FAA usage of the acronyms?
>
>3. If the FAA does use them, is the usage consistent with the
>definition in the P/CG?
>
>4. If the FAA does not use them, why are they defined?
>
I just did a keyword search in the FARs (part 1, 61 and 91) and found no
reference to IMC. VMC is defined in part 1 as "minimum control speed with
the critical engine inoperative." There is no other reference to VMC.
I think the words IMC and VMC are used interchangeably with 'IFR weather
conditions' and 'VFR weather conditions'.
--
Andrew Sarangan
PP-ASEL-IA
nightjar
Andrew M. Sarangan <sara...@unm.edu> wrote in article
<6aiiq9$2g...@musca.unm.edu>...
>
> I just did a keyword search in the FARs (part 1, 61 and 91) and found no
> reference to IMC. VMC is defined in part 1 as "minimum control speed with
> the critical engine inoperative." There is no other reference to VMC.
>
> I think the words IMC and VMC are used interchangeably with 'IFR weather
> conditions' and 'VFR weather conditions'.
>
In the UK, Visual Meteorological Conditions are defined in Article 118 of
the Air Navigation Order as 'weather permitting flight in accordance with
the Visual Flight Rules'. Instrument Meteorological Conditions are
similarly defined as ' weather precluding flight in compliance with the
Visual Flight Rules'.
Colin Bignell
Newps
As a controller I don't care what the regs say about VMC in IMC, or
whether it's even possible to be VMC/VFR in class A. If I ask you your
flight conditions and you say VMC to a controller that means 1000 and 3
or better. Period. All this crap about about above FL180 VMC/VFR not
defined is irrelevant. If I ask your flight conditions and you give me
some drivel about VMC/VFR in class A I swear I'll reach through your
headset cord and choke you to death.
Darrell Schmidt
> There has been an ongoing discussion in rec.aviation.ifr about the
> definitions of IMC and VMC. The pilot/controller glossary mentions
> "conditions ... equal to or better than specified minima" but gives no
> reference to these minima. Some pilots believe IMC means you can't fly
> by visual reference. The debate is endless.
>
> Here's the question - does anyone really use these terms? If so, what do
> they mean to you? Do you know of any references to VMC or IMC in the
> FARs or AIM? How about anywhere else (advisory circulars, weather
> manuals, etc.)?
In Vietnam, military aircraft flew IMC (Instrument Meteorological
Conditions) under VFR (Visual Flight Rules) except, of course for the
required weather. While IFR aircraft were controlled by Saigon ATC using
IFR hemispheric altitude separation (odd or even thousands), Tactical
Military Aircraft were controlled by the Fire Control radars and we flew in
the clouds at VFR altitudes (odd + 500 Eastbound and even +500 Westbound.
We did this primarily in the boondocks but we also operated close to heavy
trafficked areas.
When an aircraft is operating IFR in VMC (Visual Meteorological Conditions)
the pilot is required to maintain visual surveillance for other aircraft
even though he is under ATC control. Commercial airlines operate IFR
regardless of the actual weather. The whole U.S. could be CAFB (Clear As a
Fu--ing Bell) and all airline aircraft would be under IFR control although
EVERYONE would be in VMC.
So IMC and VMC describe the actual flight conditions while IFR and VFR
describe the Rules and level of control you are operating under. In the
U.S. there is still some low altitude airspace where ATC does not exercise
control. On my last reading of the regs, an IFR qualified pilot, flying an
IFR equipped aircraft in uncontrolled airspace could legally fly in IMC
without an ATC clearance since there is no one available to control his IFR
flight. He should fly IFR hemispheric altitudes to increase his safety
against other aircraft also flying in the clouds without ATC clearance.
Before entering controlled airspace he would have to contact ATC and obtain
clearance if he were still in IMC.
--
My Home Page: http://home.pacbell.net/schmidt/ (B-58 "Hustler")
Steven P. McNicoll
Newps wrote in message <34CCD9F7...@mcn.net>...
>
> As a controller I don't care what the regs say about VMC in IMC, or
>whether it's even possible to be VMC/VFR in class A. If I ask you your
>flight conditions and you say VMC to a controller that means 1000 and 3
>or better. Period.
>
1000 what?
MLopata
Chad R. Speer writes:
>I am going to follow through with this to the FAA and see if I can find
out a
>few things:
No, Chad, don't do it! Let's fight about it for a few more weeks first ¦-»
... just kidding. Great idea.
John Gretzinger
Chad R. Speer wrote:
>
{snip}
>
> 1. What do VMC and IMC *really* mean?
>
>
> If anyone *knows* the answer to any of these questions, please post. It
> just seems silly to have such vaguely defined terms in our vocabulary
> when we are used to dealing with rather exact meanings. I'm serious
> about following up with the FAA on this, so I want to gather all the
> information I can now.
>
> Chad Speer
> PP-ASEL, ATCS
Are you serious?
VMC is Visual Meterological Conditions - the state where Visual Flight
Rules are followed (see FAR 91.155 and following for complete
defination)
IMC is Istrument Meterological Conditions - the state where Instrument
Flight Rules are followed (again see FAR 91.167 or by extension, those
conditions other than defined in 91.155, et al.)
Didn't they teach you this in ground school???
John
--
John D. Gretzinger
Hughes Space and Communications
WARNING: Unsolicited commercial e-mail: $500 per message:
US Code, Title 47 Section 227
http://www.law.cornell.edu/uscode/47/227.html
Remove ".nospam" for return address
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Darrell Schmidt
> Chad R. Speer wrote:
> >
> {snip}
>
> > 1. What do VMC and IMC *really* mean?
> >
> > If anyone *knows* the answer to any of these questions, please post. It
> > just seems silly to have such vaguely defined terms in our vocabulary
> > when we are used to dealing with rather exact meanings. I'm serious
> > about following up with the FAA on this, so I want to gather all the
> > information I can now.
> >
> > Chad Speer
> > PP-ASEL, ATCS
>
> Are you serious?
>
> VMC is Visual Meterological Conditions - the state where Visual Flight
> Rules are followed (see FAR 91.155 and following for complete
> defination)
>
> IMC is Istrument Meterological Conditions - the state where Instrument
> Flight Rules are followed (again see FAR 91.167 or by extension, those
> conditions other than defined in 91.155, et al.)
This is not a courteous response to the question asked. VMC is NOT the state
where Visual Flight Rules are followed. Many aircraft operate under IFR in
VMC. It is REQUIRED for air carrier aircraft.VMC is the state where Visual
Flight Rules MAY be followed IF it is appropriate. Above FL 180 in the
continental U.S. it may be VMC but ALL aircraft in that airspace must operate
under IFR rules.
Roger Halstead
Darrell Schmidt wrote in message <6am56d$6k4$1...@nnrp2.snfc21.pbi.net>...
>John Gretzinger wrote:
>
>> Chad R. Speer wrote:
>> >
>> {snip}
>> > Chad Speer
>> > PP-ASEL, ATCS
<still more stuff deleted>
>> VMC is Visual Meterological Conditions - the state where Visual Flight
>> Rules are followed (see FAR 91.155 and following for complete
>> defination)
Yes, but Part 91.155 does not define VMC and IMC, It only defines the
criteria "VFR" minimums.
<more deleted>
>
>This is not a courteous response to the question asked
<some good stuff deleted with which I heartily agree>
By definition, as I understand it, but have also been unable to find in
either the FAR or AIM, IMC as mentioned above is Instrument Mererological
conditions and denotes any conditions less than those proscribed for VMC
which is of course Visual Meterological conditions whose limitations are the
same as VFR limitations listed in the FARs.
But my understanding of the original question is where are IMC and VMC
defined and I don't know.
I have gone through the FARs and AIM but have yet ot find these specifically
defined.
Contratry to what some had listed they are definitions of weather conditions
only and do not specifically indicate IFR, or VFR.
Although I know of many instances where IFR is flown in VMC conditions, the
only operations of VFR rules in IMC that I've heard of were military
operations. The FARs specifically say thou shalt not enter instrument
conditions while flying under VFR rules stateside.
Any one care to comment about taking off in IMC conditions in an
uncontrolled area?
Roger Halstead K8RI and EAA Chapter 1093 Historian
N833R World's oldest Debonair? S# CD-2
http://members.tm.net/rdhalste
MLopata
Roger Halstead writes:
>By definition, as I understand it, but have also been unable to find
>in either the FAR or AIM, IMC
Should someone have a hard-copy, or the interest to research this on the
Internet, perhaps the answer lies in the Preamble to the CFR for Title 14.
Over the years I have found the answers to some off-the-wall questions there.
John Gretzinger
>
{snip}
> By definition, as I understand it, but have also been unable to find in
> either the FAR or AIM, IMC as mentioned above is Instrument Mererological
> conditions and denotes any conditions less than those proscribed for VMC
> which is of course Visual Meterological conditions whose limitations are the
> same as VFR limitations listed in the FARs.
>
>This is not a courteous response to the question asked
Yeah, I guess that was a sort of cheap shot and for that I apologize
(bet you don't see that much in NGs). But, it still leads me to wonder
where that was in the training process (OK, so it is not part of the
required instructional material, but it is, if not necessary, at least
nice to know information). I know I taught it to my students.
> But my understanding of the original question is where are IMC and VMC
> defined and I don't know.
> I have gone through the FARs and AIM but have yet ot find these specifically
> defined.
>
{more snipping}
I don't believe you will find those definitions in any government
publication relating to flying or definitions for FARs etc. Where you
may find them is in various Meteorology books and those that teach
Aviation Weather.
I can sort of remember when I first started hearing those terms and the
initial confusion between IFR and IMC (sometime between '70 and '80).
IMC and VMC are simply vehicles/terms for describing the weather
conditions that result in a specific set of flight rules (FARs) that
must be followed.
The FAA does not care about the weather per se, only how to make the
skies safe under various flight conditions, thus FAR 91.xxx.
> >My Home Page: http://home.pacbell.net/schmidt/ (B-58 "Hustler")
Nice page --- I have always liked the Hustler - once had a model that
dropped the center store. One of my fonder childhood memories :-).
Steven P. McNicoll
Roger Halstead wrote in message <6amg2c$9...@news.dx.net>...
>Darrell Schmidt wrote in message <6am56d$6k4$1...@nnrp2.snfc21.pbi.net>...
>>John Gretzinger wrote:
>>
>>> Chad R. Speer wrote:
>>> >
>>> {snip}
><more stuff deleted>
>>> > Chad Speer
>>> > PP-ASEL, ATCS
>
><still more stuff deleted>
>>> VMC is Visual Meterological Conditions - the state where Visual Flight
>>> Rules are followed (see FAR 91.155 and following for complete
>>> defination)
>
>Yes, but Part 91.155 does not define VMC and IMC, It only defines the
>criteria "VFR" minimums.
>
><more deleted>
>>
>>This is not a courteous response to the question asked
>
><some good stuff deleted with which I heartily agree>
>
>By definition, as I understand it, but have also been unable to find in
>either the FAR or AIM, IMC as mentioned above is Instrument Mererological
>conditions and denotes any conditions less than those proscribed for VMC
>which is of course Visual Meterological conditions whose limitations are
the
>same as VFR limitations listed in the FARs.
>
>But my understanding of the original question is where are IMC and VMC
>defined and I don't know.
>I have gone through the FARs and AIM but have yet ot find these
specifically
>defined.
>
IMC and VMC are defined in the Pilot/Controller Glossary section of the AIM
and FAA Order 7110.65.
INSTRUMENT METEOROLOGICAL CONDITIONS- Meteorological conditions expressed in
terms of visibility, distance from cloud, and ceiling less than the minima
specified for visual meteorological conditions.
VISUAL METEOROLOGICAL CONDITIONS- Meteorological conditions expressed in
terms of visibility, distance from cloud, and ceiling equal to or better
than specified minima.
>
>Contratry to what some had listed they are definitions of weather
conditions
>only and do not specifically indicate IFR, or VFR.
>Although I know of many instances where IFR is flown in VMC conditions, the
>only operations of VFR rules in IMC that I've heard of were military
>operations. The FARs specifically say thou shalt not enter instrument
>conditions while flying under VFR rules stateside.
>
>Any one care to comment about taking off in IMC conditions in an
>uncontrolled area?
>
Operating in IMC under IFR is permitted in uncontrolled airspace.
Rod 510084855 Steidinger
Ever hear of a "Special VFR" Clearance? 1 mile Visibility and
"Clear of Clouds" just like in uncontrolled airspace. A Special VFR
IS in instrument conditions in controlled airspace. Kids, don't
try this at home unless you a)are instrument rated, or
b)instrument rated........R.
CMSGBEATY
Newps wrote in message <34CCD9F7...@mcn.net>...
> As a controller I don't care what the regs say about VMC in IMC, or
>whether it's even possible to be VMC/VFR in class A. If I ask you your
>flight conditions and you say VMC to a controller that means 1000 and 3
>or better. Period. All this crap about about above FL180 VMC/VFR not
>defined is irrelevant. If I ask your flight conditions and you give me
>some drivel about VMC/VFR in class A I swear I'll reach through your
>headset cord and choke you to death.
>
What a great flame, had me goin' for a while. I'll give you a 9.8.
ronca...@writeme.com
In article <34D009...@earthlink.net>,
Yes I have. Why do you ask?
>
> 1 mile Visibility and
> "Clear of Clouds" just like in uncontrolled airspace. A Special VFR
> IS in instrument conditions in controlled airspace.
>
Or it's like VMC in uncontrolled airspace. All depends on your point of
view.
>
> Kids, don't
> try this at home unless you a)are instrument rated, or
> b)instrument rated........R.
>
No SVFR unless you're instrument rated? Why?
> > >
> >
> > Operating in IMC under IFR is permitted in uncontrolled airspace.
-------------------==== Posted via Deja News ====-----------------------
http://www.dejanews.com/ Search, Read, Post to Usenet
Darrell Schmidt
> Nice page --- I have always liked the Hustler - once had a model that
> dropped the center store. One of my fonder childhood memories :-).
>
Glad you liked it, John. Did you try any of the Links I had on that page? I didn't want to be in SAC (I also flew the B-47 and
B-52H) but at least in the Hustler there was only 1 pilot so you didn't have to give away every other landing. It was nice to
fly using a stick again, too.
--
Doug Pierce
Newps wrote in message <34CCD9F7...@mcn.net>...
> As a controller I don't care what the regs say about VMC in IMC, or
>whether it's even possible to be VMC/VFR in class A. If I ask you your
>flight conditions and you say VMC to a controller that means 1000 and 3
>or better. Period. All this crap about about above FL180 VMC/VFR not
>defined is irrelevant. If I ask your flight conditions and you give me
>some drivel about VMC/VFR in class A I swear I'll reach through your
>headset cord and choke you to death.
>
Does this method work for pilots to choke controllers who give lousy
vectors? :-)
Doug Pierce
>> > >
>> > >Any one care to comment about taking off in IMC conditions in an
>> > >uncontrolled area?
You need to have a clearance issued before you take off.
>> Ever hear of a "Special VFR" Clearance?
>>
>
>Yes I have. Why do you ask?
>>
>> 1 mile Visibility and
>> "Clear of Clouds" just like in uncontrolled airspace. A Special VFR
>> IS in instrument conditions in controlled airspace.
>>
>
>Or it's like VMC in uncontrolled airspace. All depends on your point of
>view.
>
>
>>
>> Kids, don't
>> try this at home unless you a)are instrument rated, or
>> b)instrument rated........R.
>>
>No SVFR unless you're instrument rated? Why?
>
Technically, I believe you can without an instrument ticket, but I'ld have
to say follow conditions a) and b) unless you know the weather is beautiful
at the end of the runway.
ronca...@writeme.com
In article <6b1fg1$ooq$1...@news.megsinet.net>,
"Doug Pierce" <dpi...@megsinet.net> wrote:
>
> >> > >
> >> > >Any one care to comment about taking off in IMC conditions in an
> >> > >uncontrolled area?
>
> You need to have a clearance issued before you take off.
>
A clearance is required only in controlled airspace. If you are in an
area where the floor of controlled airspace is high enough so that you
can comply with FAR 91.177(a)(2) without entering the overlying
controlled airspace, then you can operate IFR without a clearance.
FAR 91.173 ATC clearance and flight plan required. No person may
operate an aircraft in controlled airspace under IFR unless that person
has-- (a) Filed an IFR flight plan; and (b) Received an appropriate ATC
clearance.
FAR 91.177 Minimum altitudes for IFR operations. (a) Operation of
aircraft at minimum altitudes. Except when necessary for takeoff or
landing, no person may operate an aircraft under IFR below-- (1) The
applicable minimum altitudes prescribed in Parts 95 and 97 of this
chapter; or (2) If no applicable minimum altitude is prescribed in those
parts-- (i) In the case of operations over an area designated as a
mountainous area in part 95, an altitude of 2,000 feet above the highest
obstacle within a horizontal distance of 4 nautical miles from the course
to be flown; or (ii) In any other case, an altitude of 1,000 feet above
the highest obstacle within a horizontal distance of 4 nautical miles
from the course to be flown. However, if both a MEA and a MOCA are
prescribed for a particular route or route segment, a person may operate
an aircraft below the MEA down to, but not below, the MOCA, when within
22 nautical miles of the VOR concerned (based on the pilot's reasonable
estimate of that distance). (b) Climb. Climb to a higher minimum IFR
altitude shall begin immediately after passing the point beyond which
that minimum altitude applies, except that when ground obstructions
intervene, the point beyond which that higher minimum altitude applies
shall be crossed at or above the applicable MCA.
> >> Ever hear of a "Special VFR" Clearance?
> >>
> >
> >Yes I have. Why do you ask?
> >>
> >> 1 mile Visibility and
> >> "Clear of Clouds" just like in uncontrolled airspace. A Special VFR
> >> IS in instrument conditions in controlled airspace.
> >>
> >
> >Or it's like VMC in uncontrolled airspace. All depends on your point of
> >view.
> >
> >
> >>
> >> Kids, don't
> >> try this at home unless you a)are instrument rated, or
> >> b)instrument rated........R.
> >>
> >No SVFR unless you're instrument rated? Why?
> >
>
> Technically, I believe you can without an instrument ticket, but I'ld have
> to say follow conditions a) and b) unless you know the weather is beautiful
> at the end of the runway.
>
I was asking Mr. Steidinger why he was opposed to SVFR flight unless the
pilot is instrument rated. An instrument rating is required for SVFR
flight only between sunset and sunrise.
FAR 91.157 Special VFR weather minimums. (a) Except as provided in
appendix D, section 3, of this part, special VFR operations may be
conducted under the weather minimums and requirements of this section,
instead of those contained in Sec. 91.155, below 10,000 feet MSL within
the airspace contained by the upward extension of the lateral boundaries
of the controlled airspace designated to the surface for an airport. (b)
Special VFR operations may only be conducted-- (1) With an ATC
clearance; (2) Clear of clouds; (3) Except for helicopters, when flight
visibility is at least 1 statute mile; and (4) Except for helicopters,
between sunrise and sunset (or in Alaska, when the sun is 6 degrees or
more below the horizon) unless-- (i) The person being granted the ATC
clearance meets the applicable requirements for instrument flight under
part 61 of this chapter; and (ii) The aircraft is equipped as required
in Sec. 91.205(d). (c) No person may take off or land an aircraft (other
than a helicopter) under special VFR-- (1) Unless ground visibility is
at least 1 statute mile; or (2) If ground visibility is not reported,
unless flight visibility is at least 1 statute mile.