Visibility - Actual vs Reported

inav8r

inav8r

Line Up and Wait
Joined
Feb 14, 2005
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Indiana, US
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Display name:
Mike B.
This morning I decided to take a leisurly cruise just after dawn. Upon waking up I looked outside to see a beautiful sunrise and CAVU conditions.

Soo, when when I'm finally ready to taxi I turn on AWOS to verify that indeed the winds are calm, and I hear, "VISIBILITY 2 MILES, HAZE". The tower has recently changed their hours and the tower wasn't yet open - so that puts the field under class E - and I was embarassingly not sure if I could legally take off.

I have a picture and maybe I'll post it later of a small patch of ground fog that had formed - basically - right on top of the AWOS equipment...

So, I shut down and waited about 20 minutes for the sun to come up farther and start to burn it off. As soon as the AWOS said 3 miles I started back up and got out of there.

So my question is, if there's a report on the field that is obviously wrong - and there's no tower to request a special from, what are your options or - better yet - what's the right thing to do?
 
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If the airport is under (but not in) Class E airspace (i.e., the shaded magenta circle showing the base of Class E at 700 AGL, not the dashed magenta lines showing Class E to the surface), you would be in Class G airspace during takeoff and legal to take off with only 2 miles ground visibility (mins of 1 mile and clear of clouds). Once airborne, your observance from the cockpit of at least 3 miles flight visibility would be adequate to continue up into the Class E airspace. Check the FAR's (section 1.1) for the definitions of flight and ground visibility.

If your airport is in Class E airspace (i.e., inside a dashed line magenta circle), you would need reported weather of at least 1000-3 to take off, and thus would be grounded until the officially reported visibility increases to at least 3 statute miles or you obtain a SVFR clearance from the ATC facility controlling the airspace in the tower's absence (usually a nearby approach control facility).
 
how fun. what part of the flight is illegal, since as soon as you break ground, the flight visibility is greater than 3 miles. it certainly isnt illegal to taxi (or fast taxi ;)) when the vis is less than Visual Flight Rules minimums without an instrument rating.
 
Ron Levy said:
If the airport is under (but not in) Class E airspace (i.e., the shaded magenta circle showing the base of Class E at 700 AGL, not the dashed magenta lines showing Class E to the surface)
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The airport (KAID) is Class D when the tower is open and is depicted with a blue dashed line on the sectional.

I supposed I could have tried to call Indianapolis approach to request SVFR - but the weather was so nice I bet the controller would have thought I was on crack... so I waited - better to be safe than sorry in regards to my ticket.

For the record - the visiblity was greater than 10 miles everywhere else in the entire state - except for the tour bus sized patch of ground haze that had formed on top of the AWOS equipment...
 
inav8r said:
The airport (KAID) is Class D when the tower is open and is depicted with a blue dashed line on the sectional.
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The question is not what it is when the tower is open, but what it is when the tower is closed. Check the A/FD for more on that. It should say whether it's E to the surface or G when tower is closed.
 
tonycondon said:
how fun. what part of the flight is illegal, since as soon as you break ground, the flight visibility is greater than 3 miles. it certainly isnt illegal to taxi (or fast taxi ;)) when the vis is less than Visual Flight Rules minimums without an instrument rating.
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If the airport is Class E to the surface when the tower is closed, the part involving the takeoff would be illegal. See 14 CFR 91.155(d)(1). Flight visibility doesn't take over for that unless ground visibility is not reported (see 14 CFR 91.155(d)(2)). Since the AWOS is reporting ground visibility, subparagraph (2) does not apply in this case. Yeah, I know that in this particular case it's downright silly, but nobody said the regs have to be not silly.
 
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Aha, thanks for all of the info Ron. According to the current A/FD, "AIRSPACE: CLASS D svc 1200-0200Z‡ other times CLASS G." Since it was 1130Z I could have departed!
 
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Ron Levy said:
If the airport is Class E to the surface when the tower is closed, the part involving the takeoff would be illegal. See 14 CFR 91.155(d)(1). Flight visibility doesn't take over for that unless ground visibility is not reported (see 14 CFR 91.155(d)(2)). Since the AWOS is reporting ground visibility, subparagraph (2) does not apply in this case. Yeah, I know that in this particular case it's downright silly, but nobody said the regs have to be not silly.
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This is curious to me. Is there somewhere that specifically says that the AWOS is to be considered right, even when its wrong?

Taking off from SAF one day, ATIS said clouds were cieling, 300ft. IN reality, the clouds burned off about 20 minutes prior.

ATC waited until the next hour to change the ATIS....
 
SkyHog said:
This is curious to me. Is there somewhere that specifically says that the AWOS is to be considered right, even when its wrong?
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The regulatory language says "reported" ground visibility. If the airport has a 3-letter ID (as in this case), the AWOS is most probably reporting the visibility to the weather system.

Taking off from SAF one day, ATIS said clouds were cieling, 300ft. IN reality, the clouds burned off about 20 minutes prior.

ATC waited until the next hour to change the ATIS....
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If so, ATC violated their own rules, which require them to change the ATIS when there is a a significant weather change as defined in their book (and going from a 300-foot ceiling to clear would qualify).
 
Ron Levy said:
The regulatory language says "reported" ground visibility. If the airport has a 3-letter ID (as in this case), the AWOS is most probably reporting the visibility to the weather system.
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Gotcha. Doesn't make sense to me that one's eyes can't trump a machine that gets confused by blowing dust, but that's the FAA for ya.

If so, ATC violated their own rules, which require them to change the ATIS when there is a a significant weather change as defined in their book (and going from a 300-foot ceiling to clear would qualify).
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Yeah, it was frustrating too, to sit in the FBO, waiting to takeoff. I didn't even think about asking for Special VFR. I sure could have remained clear of clouds, couldn't I? heh.
 
And remember, if you are tempted to take off under these conditions being discussed, as happens hundreds of times a day, no doubt, you will be perfectly safe. However, what you will be doing is "getting away with it." If there happens to be an FAA type there, somewhere on the airfield perhaps, he or she might just get into the mood to call you on it. Keep that in mind; something very similar to that happened to a couple of CFIs and their students one beautiful Saturday morning, few yr. back, at an airport near ours where pilots often go to shoot landings. I don't recall what, if any, penalty the CFIs suffered, but they were "busted" for taking off and landing in Class E, blue skies, calm, warm, but with a small area of haze/fog in one area nearby, too nearby for legality according to the fed who was out there to do some fun flying in his own little 140. Once these pilots were up at pattern altitude [or even lower], it was CAVU and any pilot ever certificated could have flown absolutely safely but it was technically below min's.
 
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