judging alt of an antenna ?

[lawndart]

I'm a fairly new base jumper, and I have just moved to east tx, I found an antenna, and I'mn not sure of the alt, I have looked at a sectional and I'm fairly sure I have spotted it at 420' but I'm not sure, it has two flashing white light's, and is free standing, what distance are the flashing light's from eachother, and what else can I do to varify the alt before attempting it? please help.. there are no color's painted on it either. E-mail me @ baseromano@yahoo.com thx. for the help

[Johnny Utah]

Distances between lights vary from tower to tower. Sometimes they differ on a tower itself. So lights are not the best gage for how high it is. But once you know how high the tower is, the lights are useful to divide the total altitude up so you can figure how high you are as you go up the tower.

Sectionals are not always accurate, but are often close. A good tool to reference and compare with.

The best method (IMHO) is to use a laser rangefinder. From the ground you can aim it at the exit point to get an altitude. A lot of times you wont be right under the exit point, but measuring with an angle from where youre standing to the exit point, so the distance will read a little higher than it is. If you measure it while on top, you can aim it straight down from the exit point to point of impact. This will give the most accurate altitude.

Altimeter watches work fairly well. Pressure changes do happen which throw it off a little bit, but they give a pretty good idea of how high you are.

A bit of advice I can give ya:
If youre not sure of the actual altitude, then error to the side of thinking its lower.

Its better to have too long of a canopy ride, than too short of a canopy ride.

[Nick_D]

All painting and lighting of towers, smokestacks, chimneys, etc., are governed by FAA Advisory Circular AC 70/7460-1K and applies to any such structure over 200-feet. The FCC also goes by the same regulations. You can download it here:

http://www.faa.gov/ats/ata/ai/index.html

I warn you though; this is written in pure government gobbledygook.

The fact your tower is not painted, or color banded as they call it, even though the structure is higher than 200-feet is what makes using these clues NOT always a reliable measure of height. The FAA says, essentially, if the tower is in the middle of nowhere these rules can be waived. On the other hand when a tower is close to a low altitude airway, or airport the rules are more stringent.

Here's how color banding works in a nutshell. The number of color bands (alternating orange and white) is determined by the height of the tower. A 700-foot tower will have 7 bands of alternating color. An 1100-foot tower will have 11 bands. You get the idea the bands on your 400-footer (if it was banded) would be four.

I got such a headache reading this far into the regulations I passed on the section that deals with lighting, I leave that for you.

One more tip. When you look at the sectional again you may see two numbers near the tower symbol, one is altitude above "mean sea level" (MSL) and the other is the altitude "above ground level" (AGL) so don't mix them up.

There are also various range finding devices available, like laser and certain types of spotting scopes, but if all else fails there's always the rock drop, one mississippi, two mississippi, etc. method . . .

Here's an interesting section of the rules that will be important when the day finally comes, and it will, when someone wants to erect a tower just for BASE jumping that is over 2000-feet.

"Although there is no absolute height limit for antenna towers, both agencies have established a rebuttable presumption against structures over 2,000 feet above ground level. The FCC has a policy that applications filed with the FCC for antenna towers higher than 2,000 feet above ground will be presumed to be inconsistent with the public interest and the applicant will have a burden of overcoming that strong presumption. The applicant must accompany its application with a detailed showing directed to meeting this burden. Only in the exceptional case, where the FCC concludes that a clear and compelling showing has been made that there are public interest reasons requiring a tower higher than 2,000 feet above ground, and after the parties have complied with applicable FAA procedures, and the FCC and FAA have fully coordinated their actions on the question of menace to air navigation, will a grant be made."

I want to be there when the attorney has to argue BASE jumping is in the public interest . . .

NickD
BASE 194

[Faber]

get your self a alti watch (suuonto silva or alike) or even better get your self a laser ranger

[Mac]

you dont have to be right under the exit or on top to get an accurate measurement of height with a Laser range finder. Just use Pythagoras Theorem to calculate the height.

[Karskland]

climb it and throw a rock...