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I'm not really sure how to ask my question, but there are classifications for weather conditions for MVFR, IFR, and LIFR. The FAA also has weather minimums for flying VFR in the different airspaces here.

What is the difference between when we would use one over the other? If I am departing from an airport in class bravo airspace, would I need three statute miles of visibility and remain clear of clouds (second link), or would I also need to adhere to the minimum VFR ceiling of 1000' (first link)?

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  • $\begingroup$ FWIW, the two links you posted are talking about different things. The first tells you how weather conditions are classified for display in weather reports. The second tells you what cloud clearance you need to maintain while airborne. So it doesn't make much sense to compare them directly. I don't know if that's useful, but maybe it can help you to narrow down what you're trying to ask. $\endgroup$ – Pondlife Sep 25 '18 at 2:03
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The FAA does not define "LIFR" or "MVFR"

These are not terms that the FAA makes reference to. Go look in the FAR/AIM, section 1.2. You'll find VFR defined, and IFR defined, but not the other two. Why is that?

Because those are terms used by the National Weather Service, not the FAA

That means that if you want to operate an aircraft, you obey the FAA weather minumums that are provided in your second link.

The information in the first link is about reading weather reports. As far as the FAA is concerned:

  • VFR is VFR
  • MVFR is also VFR
  • IFR is IFR
  • LIFR is also IFR

So answer my question

Ok. If you're departing from an airport, and you will be in class B airspace from the moment your wheels leave the ground, then as long as you have 3 miles visibility and you don't touch a cloud you can fly.

However, it's not likely that you'll be in class B airspace from the moment you leave the ground unless you're departing from the main airport (LAX, ORD, and so on) and if that's the case odds are you're on an instrument flight plan anyway.

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There are two FARs that govern takeoff. The first is §91.155 and quite clearly states that no one may take off under VFR (except at Class G airports) if the ceiling is less than 1,000'. You could ask for a Special VFR, but you won’t get it at Class B—in fact many (most?) have a notation on the chart saying that it is not allowed.

The second FAR is §91.175 (f) governs visibility in IFR operations and does not apply to Part 91 operations (which I assume you are).

So assuming you want to depart VFR, you would need 1,000' ceiling to depart. If you want to depart IFR, you can do so with 0 ceiling and 0 visibility. (Subject to any conditions in the Obstacle Departure Procedure §91.175 (f)(3)).

§91.155 Basic VFR weather minimums.

(c) Except as provided in §91.157, no person may operate an aircraft beneath the ceiling under VFR within the lateral boundaries of controlled airspace designated to the surface for an airport when the ceiling is less than 1,000 feet.

(d) Except as provided in §91.157 of this part [Special VFR—which you won’t get at a Class B airport], no person may take off or land an aircraft, or enter the traffic pattern of an airport, under VFR, within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport—

(1) Unless ground visibility at that airport is at least 3 statute miles; or

(2) If ground visibility is not reported at that airport, unless flight visibility during landing or takeoff, or while operating in the traffic pattern is at least 3 statute miles.

(e) For the purpose of this section, an aircraft operating at the base altitude of a Class E airspace area is considered to be within the airspace directly below that area.

§91.175 Takeoff and landing under IFR.

(f) Civil airport takeoff minimums. This paragraph applies to persons operating an aircraft under part 121, 125, 129, or 135 of this chapter.

(1) Unless otherwise authorized by the FAA, no pilot may takeoff from a civil airport under IFR unless the weather conditions at time of takeoff are at or above the weather minimums for IFR takeoff prescribed for that airport under part 97 of this chapter.

(2) If takeoff weather minimums are not prescribed under part 97 of this chapter for a particular airport, the following weather minimums apply to takeoffs under IFR:

(i) For aircraft, other than helicopters, having two engines or less—1 statute mile visibility.

(ii) For aircraft having more than two engines— 1⁄2 statute mile visibility.

(iii) For helicopters— 1⁄2 statute mile visibility.

(3) Except as provided in paragraph (f)(4) of this section, no pilot may takeoff under IFR from a civil airport having published obstacle departure procedures (ODPs) under part 97 of this chapter for the takeoff runway to be used, unless the pilot uses such ODPs or an alternative procedure or route assigned by air traffic control.

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Sounds like you wish to depart VFR.

would I need three statute miles of visibility and remain clear of clouds (second link)

Is that Special VFR? Special VFR might be a little less restrictive even. You can request Special VFR, but it will never be offered (explicitly) to you from ATC.

The Special VFR requirements, to be complete:

14 CFR 91.157 - Special VFR weather minimums. eCFR Authorities (U.S. Code) Rulemaking What Cites Me prev | next § 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 § 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 § 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. For the purposes of this paragraph, the term flight visibility includes the visibility from the cockpit of an aircraft in takeoff position if:

(i) The flight is conducted under this part 91; and

(ii) The airport at which the aircraft is located is a satellite airport that does not have weather reporting capabilities.

(d) The determination of visibility by a pilot in accordance with paragraph (c)(2) of this section is not an official weather report or an official ground visibility report.

[Amdt. 91-235, 58 FR 51968, Oct. 5, 1993, as amended by Amdt. 91-247, 60 FR 66874, Dec. 27, 1995; Amdt. 91-262, 65 FR 16116, Mar. 24, 2000]

91.205(d) basically says you have to be equipped for VFR and have a radio. https://www.ecfr.gov/cgi-bin/text-idx?pitd=20170830&node=se14.1.91_1205&rgn=div8

So clear of clouds and 1 mile visibility - sounds more like scud running to me.

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  • $\begingroup$ Do you mean that the first link is about takeoff weather minimums, and the second link is about flying within the different airspace classes? $\endgroup$ – slantalpha Sep 25 '18 at 1:29
  • $\begingroup$ The first is not just takeoff, but flying in those conditions period. Are you a pilot? $\endgroup$ – CrossRoads Sep 25 '18 at 1:59
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    $\begingroup$ @CrossRoads - Don't most class B airports have NO SVFR as a restriction? $\endgroup$ – Steve V. Sep 25 '18 at 4:55
  • $\begingroup$ I don't know. I don't use Class B airports - too much jet traffic, landing fees, high fuel costs. I went thru the Departures for BOS, which is 25-30 miles away, and the TAKEOFF MINIMUMS, (OBSTACLE) DEPARTURE PROCEDURES, AND DIVERSE VECTOR AREA (RADAR VECTORS) ,and I didn't see No SVFR listed anyplace. $\endgroup$ – CrossRoads Sep 25 '18 at 15:33
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    $\begingroup$ @CrossRoads - Among other places, it's on the sectional chart $\endgroup$ – Steve V. Sep 26 '18 at 3:31

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