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I have a question regarding flying in the Yosemite Valley national park, which I flew over last weekend in an open-cockpit gyroplane.

The sectional states you must be a minimum of 2,000 ft about the highest point within 2,000 feet of you. The famous valley itself, containing El Capitan and Half Dome, has a highest point of 8,800ft or so, so when I flew it, I was at well over 10,000 ft.

However, it occurred to me afterwards, that if the valley is actually more than 4,000 ft wide (which it is), then all I needed to do was to be sure I was more than 2,000 ft above the valley floor, which is at 4,000ft.

So instead of flying over it at 10,000, I could do it at 6,000ft if I'm in the middle of the valley.

This would put me way below the peaks of El Cap and Half Dome, but provided I'm more than 2,000ft away from them, I'd be legal.

Is that correct?

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    $\begingroup$ I think this question can be more generalized as "Can I fly below the heights of mountains if I am more than 2,000 feet away from them?" $\endgroup$
    – SMS von der Tann
    Mar 16, 2017 at 18:01
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    $\begingroup$ @SMSvonderTann No, it cannot. Most mountainous areas have no special altitude or ground separation requirements under VFR. $\endgroup$
    – J W
    Mar 16, 2017 at 18:34

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Short answer: you can fly in Yosemite Valley at 500ft AGL (most likely); there's no special regulation applicable there; the wording on the sectional is a non-regulatory 'encouragement' only.

By regulation, the minimum altitudes under VFR are in 14 CFR 19.119:

(a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.

(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.

(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

I don't know what Yosemite Valley looks like and whether it's "congested" or not (see this question), but it's very likely that you could operate legally at 500ft AGL there, if not lower.

What the sectional says comes from AC 91-36, Visual Flight Rules (VFR) Flight Near Noise-Sensitive Areas. But as the AC itself says, it only encourages pilots to fly above 2000ft AGL (emphasis mine):

This Advisory Circular (AC) encourages pilots making VFR flights near noise sensitive areas to fly at altitudes higher than the minimum permitted by regulation

If you read the whole thing, you can see the not-so-hidden message:

The Federal Aviation Administration (FAA) receives complaints concerning low flying aircraft over noise sensitive areas such as National Parks, National Wildlife Refuges, Waterfowl Production Areas and Wilderness Areas. Congress addressed aircraft flights over Grand Canyon National Park in Public Law 100-91 and commercial air tour operations over other units of the National Park System (and tribal lands within or abutting such units) in the National Parks Air Tour Management Act of 2000.

[...]

Adherence to these practices is a practical indication of pilot concern for the environment, which will build support for aviation and alleviate the need for any additional statutory or regulatory actions.

In other words, 'please be responsible and considerate because if you aren't, Congress might force us to introduce more regulations like we had to do with the Grand Canyon'. Practically speaking, I guess that if you fly down Yosemite Valley at 500ft AGL every day, even if it's completely legal you can still expect a call from the FAA asking why you're doing it and 'encouraging' you ("cough 91.13 cough") to fly higher for 'safety' reasons.

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    $\begingroup$ I can't provide a reference at the moment, but I believe that there is a regulation by another government entity that does prohibit low altitude flight. I understand that the FAA's recommendations are an encouragement to follow these other regulations that fall outside their jurisdiction. $\endgroup$
    – J W
    Mar 16, 2017 at 23:48
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    $\begingroup$ @JonathanWalters It would be great if you can find it, I don't remember it coming up on the site yet $\endgroup$
    – Pondlife
    Mar 17, 2017 at 0:20
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    $\begingroup$ I think parts of Yosemite Valley would qualify as congested and/or settlement, given all of the campgrounds and parking lots. And common sense tells me that going through there at 500 ft would get you a terrific amount of unwanted attention regardless. $\endgroup$
    – stevegt
    Mar 17, 2017 at 0:31
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    $\begingroup$ Look here at 7-4-6 (3)(c) nearly at the bottom of the page: "Federal statutes prohibit certain types of flight activity..." Sorry, I'm not in a great spot for further digging just now. $\endgroup$
    – J W
    Mar 17, 2017 at 0:40
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    $\begingroup$ See also the (as possibly relevant) "The National Parks Overflight Act of 1987" $\endgroup$
    – J W
    Mar 17, 2017 at 1:24
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(Edit: removed text about "legality") Flying "down into the valley" (even if laterally separated from all sides by more than 2000 feet, and remaining more than 2000 feet above the surface) goes against the FAA's suggested altitude when "overflying a national park", with this paragraph from AC 91-36:

For the purpose of this AC, the ground level of noise-sensitive areas is defined to include the highest terrain within 2,000 feet AGL laterally of the route of flight, or the uppermost rim of a canyon or valley.

The FAA requests and recommends that pilots stay 2000 feet above the "upper most rim of the valley". However, as others have said, this is just an "advisory" circular, and not a legal requirement.

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    $\begingroup$ AC's are advisory in nature, not like FAR's which have legal ramifications. AC's are FAA's recommendation, not necessarily defining legal/illegal. I'm not sure if this AC clarifies an FAR or not, I didn't see an FAR reference in the AC. $\endgroup$
    – Ron Beyer
    Mar 16, 2017 at 20:31
  • $\begingroup$ This does not provide an answer on the legality in question. As has already been pointed out, ACs are advisory only. $\endgroup$
    – J W
    Mar 16, 2017 at 23:49
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    $\begingroup$ Yep, good catch on "legality" - this is just an AC. Public Law 100-91 (1987) mandated the study of NPS overflights, and also specified that flights in Yosemite Valley were illegal during the study period. But that period is over, and I don't know of any specific law or FAR applying to any NPS other than the Grand Canyon. $\endgroup$
    – Jimmy
    Mar 17, 2017 at 1:27
  • $\begingroup$ Appreciate the thought into this. Seems like the consensus is that the AC (not a legal requirement) adds the "uppermost rim of valley" restriction but that's not on the sectional and because the AC is not a legal thing anyway, it's just a request. So I COULD do it, but I shouldn't if there's a risk of causing significant annoyance to park users. $\endgroup$
    – Paul Hollingworth
    Mar 17, 2017 at 20:27
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Browsing through the Soutwest Chart Supplement I ran across this:

SPECIAL NOTICES

YOSEMITE NATIONAL PARK Public law prohibits flight of VFR helicopters or fixed-wing acft below 2000 feet above the surface of Yosemite National Park. “Surface” refers to the highest terrain within the park within 2000 feet laterally of the route of flight or, within the Yosemite Valley, the uppermost rim of the valley.

I don’t know which public law they are referring to.

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    $\begingroup$ It seems to refer to PL100-91, which did ban flight below 2000' but only "During the study and review periods provided in subsection (c)", in other words, it was temporary as part of the study. Interestingly, this article shows that the restriction was actually printed on the sectional at one point, but it's now gone (if skyvector.com is current). $\endgroup$
    – Pondlife
    Apr 10, 2017 at 23:28

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