# A 91.155 puzzle

Discussion in 'Flight Following' started by Dave S., Nov 15, 2021.

1. ### Dave S.Pre-takeoff checklist

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Here is an interesting analysis that came up in my college 141 class.

91.155d requires 3 miles ground (or 3 miles flight viz in lieu of) viz to takeoff land or enter the pattern(only) at an airport for which the surface area is designated. (What is conspicuously absent is flight through the surface area.). This seems redundant seeing how 3 viz under 91.155a would apply anyway. But I digress.

9.155c states that I can not operate an aircraft within the lateral boundaries of a surface area beneath a ceiling of less than 1000 feet. Notice that it does not stipulate take off, landing, or entering the pattern for the ceiling criteria as it does with visibility, or that that 1000 foot ceiling be officially reported. Consider the reverse. If the airport called the ceiling BKN015 91.155c would prevent me from flying through the surface area if, where I was at, I was operating below a ceiling that was actually BKN006!

Here’s the question. If the airport is calling the weather as 3 miles and BKN008 and I am simply flying through the Class D AND the ceiling where I am is BKN012 then am I violating 91.155c? Would I require a SVFR in that situation? There was an amendment “97” (I believe the number was) years ago that specifically addressed this point. As I remember the amendment stated that flight through the surface area was entirely determined by pilot observations, both viz and ceiling. That amendment no longer exists that I can find.

Most responses go something like this…”The official weather determined by the tower controls the entire Class D for both viz and ceiling for purposes of 91.155c and d.”

Does it? Clearly the ground viz required in 91.155d requires an officially determined visibility and only absent that official observation can flight viz be used.
But what about the ceiling. The only requirement I see is that I do not operate beneath a less than 1000 foot ceiling.

So, if the airport observation does indeed control the ceiling for the entire surface area as well as the viz….what is the proof of that in the regs or AIM or other source?

tex

Last edited: Nov 16, 2021
2. ### luvflyinTouchdown! Greaser!PoA Supporter

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The proof is in FAR Part 1. Definitions and Abbreviations.

Ceiling means the height above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as “broken”, “overcast”, or “obscuration”, and not classified as “thin” or “partial”.

The key word here is ‘reported.’ There is no such thing as the ceiling where ‘you are.’ Only Certified Weather Observers can ‘report’ the ceiling. You may be between the breaks in a broken ceiling with blue skies above you, but that does not change the ‘ceiling.’ Of course you always have to comply with Cloud Clearance Requirements. But you can be in compliance with those and still be beneath the ‘ceiling.’ Here’s a fun Surface Area. Play around with different Weather Reports from KCLM and KNOW and how they relate to 91.155 (c) and (d).

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3. ### Clip4Final Approach

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You have 2 definitions - flight visibility and ground visibility.

Ground visibility is a reported observation. Flight visibility is an estimate made by the pilot in flight.

is it possible for the ground vis to be lower than the flight vis?

Last edited: Nov 16, 2021
4. ### luvflyinTouchdown! Greaser!PoA Supporter

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Of course. It happens often when the Tower hasn't had their windows washed in awhile

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5. ### flyingronTouchdown! Greaser!PoA Supporter

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I agree with Clippy. The reg says ground visibility which is defined as reported. If the official weather (typically the tower/AWOS in the primary airport) reports the ceiling is less than 1000, no matter whether it is or not, you may not operate VFR beneath the ceiling. You can penetrate the airspace over the top if you like. The only thing that has changed over the forty-five years I've been flying (other than the replacement of the word Control Zone with "Surface Area of Controlled Airspace Designated for an Airport") is that the words "under the ceiling" were added. I believe this was attributable to one of our board members (Are you around Dennis?).

6. ### Martin PaulyLine Up and WaitPoA Supporter

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Based on what section of §91.155? The only mentioning of ground visibility I see in there is in (d): "no person may take off or land an aircraft, or enter the traffic pattern of an airport, under VFR, ...".

So in the OP's scenario ("I am simply flying through the Class D" - i.e. not taking off, landing, or flying in the pattern) does ground visibility really apply?

- Martin

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It also happens the other way around when it's crap out. Conversation usually ends with the tower asking "well, what do you need to get in", and generally is followed by the visibility being exactly that...

8. ### flyingronTouchdown! Greaser!PoA Supporter

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Sorry, I should have said ceiling not visibility. Ceilings are always what is reported. See the definition in 1.1:

(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.

Ceiling means the height above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as broken, overcast, or obscuration, and not classified as thin or partial.

9. ### luvflyinTouchdown! Greaser!PoA Supporter

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It does not.

10. ### Martin PaulyLine Up and WaitPoA Supporter

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Note also that the "reported" part of that definition goes with "broken, overcast, or obscuration", not with the height. So one could argue that the official report declares the existence of a ceiling and its type, but the height is whatever it actually is at a given location.

- Martin

11. ### Velocity173Touchdown! Greaser!PoA Supporter

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I thought we covered this years ago with a CC letter from the 70s that states that any ceiling reported for a surface based airspace, is valid for the entire surface area. Doesn’t mean you can’t fly over it while in the surface area and not require a SVFR. Just can’t fly under it.

12. ### Martin PaulyLine Up and WaitPoA Supporter

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I tried to find this letter for I have heard it being referenced before. But I could not find it. Do you have a link to it you could share here?

Thanks.

13. ### Dave S.Pre-takeoff checklist

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Then, if the weather is reported as 3 sm and BNK005 and the layer is not very thick, say 200 feet, that would put the tops at 700. If it is clear above can I fly through the Class D above the layer, in clear blue skies, without a SVFR since I am not below a layer less than 1000 feet?

14. ### Velocity173Touchdown! Greaser!PoA Supporter

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Yeah if you’ve got your 1,000 ft above, you’re legal without a SVFR clearance.

Last edited: Nov 16, 2021
15. ### luvflyinTouchdown! Greaser!PoA Supporter

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Hmm. If it got to enforcement action, who knows, that might work. Yes your Honor, I know that only the Certified Weather Observer can determine the Sky Condition. It’s his call whether or not it is Broken or Scattered. But I get to determine the Height. See here, let’s break down this sentence in the FAR. I call Dr. Wordsworth, an acclaimed English Professor to the stand as my next witness. You might con the Judge and/or Jury into it, but I ain’t bettin’ on it.

16. ### luvflyinTouchdown! Greaser!PoA Supporter

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Yup. You’d have to be up at 1700 AGL though, because you are still bound by the 1000 feet above thang.

Last edited: Nov 16, 2021
17. ### Martin PaulyLine Up and WaitPoA Supporter

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You are right, I would not count on it, especially if a Chief Counsel's letter already exists. (I'd still love to actually SEE that letter - anybody here have a link?)

How about this: If there's a broken layer right above a towered field at 1,500 AGL and reported like that on the ATIS, and two miles north where I'm transiting the Class Delta I face a broken layer at 1,000 AGL, I am quite sure the FAA wants me to maintain cloud distance from the actual base, not the reported base. Why wouldn't that also work the other way around?

- Martin

18. ### luvflyinTouchdown! Greaser!PoA Supporter

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Of course you have to do the 1000/500/2000/3 thing if you are VFR. The restrictions about Ceilings in Surface Areas don't alter that. Why they didn't write it as you suggest, I can't say for sure. Maybe when that Head Shyster letter is found, it will have some background info about it.

19. ### midlifeflyerTouchdown! Greaser!

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There are two of them, related:

MAY 21, 1979

AGC-23
Control Zone Weather
Chief, Airspace, Air Traffic and Environmental Quality Branch, AGC-23
AAT-300

This is in response to your memo of March 23, 1979, in which you ask for guidance on the question of what weather applies when more than one station is reporting the weather within a given control zone.
There has been considerable interest over the past few years within the FAA regarding control zone VFR requirements and the extent to which reported weather should be used to determine whether VFR operation within an entire control zone should or should not be conducted. At one point, a change was even proposed to Sec. 91.105(c) which would take into consideration the possibility of varying weather in a control zone. This proposal was eventually dropped, however, because of the safety implications and the enforceability problems which it raised.
The continuing legal opinion of this office is that the reported ceiling at the primary airport in a control zone (i.e. the airport upon which the designation of the control zone is based) governs as to whether VFR operations can be conducted within that particular control zone. Even though there may be more than one weather station within a control zone, there will not be more than one at a given airport. If one of the stations is located at the primary airport, which will generally be the case, the report of that station governs. If neither of the stations is located at the primary airport (an unlikely possibility), the station used by the primary airport to determine its weather governs. This provides an enforceable precise basis for determining whether Sec. 91.105(c) has been violated.
This opinion linking "reported" ceiling to the "primary airport" in Sec. 91.105(c) has been the position of the office of the Chief Counsel for over 28 years.
No replacement concept has been proposed which has been shown to provide the same degree of safety and enforceability.
If there are airports or control zones which present special problems that are not fairly treated by this longstanding interpretation, these might be addressed on an individual basis in Part 93.
Let us know if we can provide further assistance in this matter.

/s/
RICHARD W. DANFORTH

And a year later...

OCT. 14, 1980

AGC-230
Interpretation of FAR Parts 91 and 93
Chief, Airspace and Environmental Law Branch, AGC-230
AAT-220

This is in response to your memo of October 3, 1980, asking for an interpretation of the rules governing VFR operations at Pearson Airpark when the reported weather at Portland International is below VFR minima.
The established and continuing legal opinion at this office is that the reported ceiling at the primary airport in a control zone governs as to whether VFR operations may be conducted within that particular control zone. This is the interpretation of Sec. 91.105(c) which we furnished AAT-300 in our memo of May 21, 1979 (a copy of which is enclosed for your information.)
The specific question you have asked involves reported weather at Portland International to be "indefinite ceiling, sky obscured, visibility zero, fog." The definition of "ceiling" in FAR Sec. 1.1 is as follows:
"Ceiling" means the height above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as "broken," "overcast," or "obscurated," and not classified as "thin" or "partial."
Since the "obscuring phenomena" in the subject weather report is a fog which is limiting ground visibility to zero, it is clear that the height of the lowest layer of that obscuring phenomena is lower than 1,000 feet above the earth's surface.
Accordingly, the reported ceiling at Portland International would be lower than 1,000 feet. A pilot taking off VFR from Pearson Airpark under these conditions would be in violation of Sec. 91.105(c).
We are available to provide any needed further assistance in this matter.

RONN E. HARDING
Enclosure

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20. ### Martin PaulyLine Up and WaitPoA Supporter

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Thanks, Mark. That's pretty definitive.

21. ### midlifeflyerTouchdown! Greaser!

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Of course, it was 1979-1980 a few years before AWOS began being used for weather reporting. So those interpretations are from a world where there were human observers, not a sensor looking at only a small piece of the pie.

in the B, C, D world of @Dave S.' question, the answer remains easy. Announcing, "The field is IFR" or the like, involves human interaction. I think the more interesting question is a Class E surface area when the AWOS/ASOS is shrouded (or simply wrong) but it is visually clear on the runway and in the direction you are using.

22. ### luvflyinTouchdown! Greaser!PoA Supporter

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Yeah. Those things are downright liars sometimes. I think Human Augmentation and the ability to transmit METAR's and SPECI's is a requirement to use AWOs/ASOS to meet the weather reporting requirement for the establishment of a Surface Area.

23. ### midlifeflyerTouchdown! Greaser!

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Class E surface areas require a way to communicate with ATC and weather observation and reporting, but it does not have to be a human observer. This is from Order 7400.2N (it mentions Class D. The section on Class E surface areas refers back to it instead of repeating):

Weather observations must be taken at the primary airport during the times and dates the Class D airspace is active. A federally certified weather observer or a federally commissioned automated weather observing system (this includes all FAA and NWS approved and certified weather reporting systems) can take the weather observation. The weather observer must take routine (hourly) and special observations. An automated weather observing system can provide continuous weather observations.​

I used to know this much better but, basically, approved AWOS systems output code to fit the METAR format and feed it into the system.

KTTA 171515Z AUTO 00000KT 10SM CLR 16/08 A3030 RMK AO2 T01630078

The "AUTO" means no human intervention in the report. If there was human intervention it will be "COR" (corrected) instead.

Last edited: Nov 17, 2021
24. ### bflynnFinal Approach

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Wow, so if you don't catch the ground fog at the class-E surface level airport, you can technically fly into non VFR conditions with 100 miles of visibility, 1000' above the clouds and clear above.

25. ### MauleSkinnerTouchdown! Greaser!

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They’re not non-VFR conditions.

26. ### luvflyinTouchdown! Greaser!PoA Supporter

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Thx