That's really interesting.
Jim Lux already mentioned the pitfalls of GPS and barometric measurements of
altitude. The technology of ILS doesn't require a functioning altimeter to
land and I don't believe IFR rules allow landing without some minimum
visibility - enough to render a functioning altimeter "optional" on approach.
The point being that no one expects a barometric altimeter to be accurate
enough to be the only reference for height above ground as you land.
Many, if not most, USGS elevation benchmarks were set using a rod and level
starting in the 19th century. They are surprisingly accurate considering that
those in the middle of the country are more than a thousand miles from the
nearest ocean.
As an aside, I thought I had read that Google Earth had a problem with
elevations. I don't remember the exact circumstances, but the context was some
sort of modeling as GE assumes a spherical earth. Basically, GE underestimates
altitudes and sea levels at low latitudes due to the "bulging" of the earth at
the equator. That sound familiar to anyone?
Al
AB2ZY
________________________________________
From: towertalk-bounces@contesting.com [towertalk-bounces@contesting.com] On
Behalf Of Mike Ashby [seabassm01@hotmail.com]
Sent: Friday, December 30, 2011 11:49 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] FAA & Private Airstrips
Bill;
I just finished making application to the FAA and after about 60 days received
back a "Notice of presumed HAZARD to air navigation" letter from them. This
has since has been resolved and I now have received the go ahead to install a
tower. QTH is 5572 feet south of a very small municipal airport. Tower
location falls in the first ring around the airport marked by the FAA as
"Horizontal Surface elevation: 150 feet". 10 feet further east on my 10 acre
property begins the outer ring around the airport marked "Conical Surface 20:1"
One would think that in the 1st ring the tower could be 150 ft in height and in
the 2nd ring it could be 278 ft in height, (5572/20)...........I did. Started
application by taking some quick elevation measurements with GPS unit and made
application for a 120 foot tower, it was rejected. After long discussion with
FAA, took a trip over to the airport to talk with the manager. I wanted to
find the airport elevation marker for the airstrip. They didn't know where it
was. The sign at the entrance to the property posted the elevation as 5680 ft.
The FAA shows it as 5637 ft. I asked a pilot of a small commercial jet, that
was sitting of the airstrip what his altimeter was reading and he said 5605 ft.
(That would be 32 ft below the official FAA surface of the runway elevation).
Went into town and found an official USGS survey marker and calibrated my GPS.
Went back to QTH and remeasured, nothing was looking good for me. Called FAA,
discussed my measurements.........decide
d I would use same thing that they were checking with...................GOOGLE
EARTH! Plugged in all of the measurements, adjusted tower height down to
110ft, (could have gone as high as 113 ft but didn't want to press my luck),
sent changes back to FAA and received approval next day. So much for the "150
ft zone" and the "20:1" zone.............never did get a good explanation as to
why not, just happy to get what I got.
Mike
> From: himself@edhaggerty.com
> Date: Fri, 30 Dec 2011 10:50:10 -0500
> To: bill.aa7xt@gmail.com
> CC: towertalk@contesting.com
> Subject: Re: [TowerTalk] FAA & Private Airstrips
>
> Bill
>
> Unless you have a deep hatred for airplanes and people who fly
> them......please contact the owner/operator of the airstrip and inform them
> of the position and hight of your tower.
>
> 73 Ed KB3TOX
>
> On 29 Dec, 2011, at 7:56 PM, William Hein wrote:
>
> > My family and I recently moved to a wonderful house in beautiful Glade Park
> > CO (on the other side of Colorado National Monument from Grand Junction.
> > The house itself is an ultra-energy efficient Earthship (Google "Glade Park
> > Earthship" for more info). We have 35 rural acres of land around our house
> > in a low population density rural area. All in all it's going to be a
> > great place for ham radio.
> >
> >
> >
> > The FAA Website TOWAIR indicated that "Structure does not require
> > registration"after I plugged in my coordinates along with elevation
> > (6840-ft ASL approx.). There are no airports within 8 kilometers (5 miles)
> > of the coordinates you provided." TOWAIR went on to caution "TOWAIR's
> > findings are not definitive or binding". Since "Pinyon Airport" (a rather
> > pretentious designation for a grass airstrip with a windsock) is 5.5 km
> > away I am guess it is either not registered with the FAA or somehow doesn't
> > count as a real airport.
> >
> > I have a 142-foot Big Bertha tower which I previously had installed in
> > Vermont which I intend to reinstall here along with at least one other
> > 100-ft + tower and a few smaller structures. For many reasons I'd hate to
> > see a airplane run into Bertha.
> >
> > So what should I do now? Contact the FAA for an opinion? Find out who
> > owns the airstrip and give them a verbal or written heads up on my tower
> > plans and also request they avoid flying low over my house? Something else?
> >
> > 73
> > Bill
> >
> > -----
> > William Hein, AA7XT
> > (ex-AA4XT, NT1Y, AA6TT, KC6EDP)
> >
> >
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
>
>
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