Minnesota Crop Duster Fatality — Clipped Radio Guy Wire
- Thread starter RDoug
- Start date
FloridaLarry
Well-Known Member
RIP
Tall broadcast towers are tensile structures - held in place by the guy wires, which are twisted steel ropes of 1/2" through 1" in diameter. They're very high-quality steel, as are the fastenings which attach them to the tower, and to humongous concrete & rebar blocks, buried in the earth under the outer end of the guy wire radials. (the size depends on the soil - larger for swampy or sandy soil, not as large for dense compacted dirt or rock). A tall tower may have two (or more) sets, inner one for the lower part of the tower and outer for the higher guys. Guys typically start some 200-300 feet above ground, and happen every 100-200 feet up to the top. Highest guy will be at the top of the tower itself, with the actual antenna, top strobe and lightning arresting gear above that, often 50-100 more feet. Usually three sets of guy wires, at 120 degree horizontal separation. TV and FM antennas are separate from the tower, either hung on the side near the top, or sticking up; AM stations generally use the top half or entire tower as the radiating antenna, and may well have several towers to create a directional signal pattern.
All this stuff is designed by a registered structural engineer. The forces at work can be tremendous! When a guy wire breaks or becomes disconnected, the tower can become unstable and other forces can bring it down. The usual suspects: wind and/or ice. Often the most vulnerable time is when guy wires are loosened for adjustment or maintenance. (They can stretch over time). Like an out-of-balance propeller, sympathetic vibration can set in.
From the picture with the attached article, the guy wire he hit held long enough to seriously bend the tower. Then the guy either broke, or the aircraft slid off it.
Fixed wing aircraft have no business near a tower. That's why they are marked on aviation sectional maps and lighted with high-power strobes. Nor do helicopters, except when they are used to erect or maintain the tower and antenna.
Tall broadcast towers are tensile structures - held in place by the guy wires, which are twisted steel ropes of 1/2" through 1" in diameter. They're very high-quality steel, as are the fastenings which attach them to the tower, and to humongous concrete & rebar blocks, buried in the earth under the outer end of the guy wire radials. (the size depends on the soil - larger for swampy or sandy soil, not as large for dense compacted dirt or rock). A tall tower may have two (or more) sets, inner one for the lower part of the tower and outer for the higher guys. Guys typically start some 200-300 feet above ground, and happen every 100-200 feet up to the top. Highest guy will be at the top of the tower itself, with the actual antenna, top strobe and lightning arresting gear above that, often 50-100 more feet. Usually three sets of guy wires, at 120 degree horizontal separation. TV and FM antennas are separate from the tower, either hung on the side near the top, or sticking up; AM stations generally use the top half or entire tower as the radiating antenna, and may well have several towers to create a directional signal pattern.
All this stuff is designed by a registered structural engineer. The forces at work can be tremendous! When a guy wire breaks or becomes disconnected, the tower can become unstable and other forces can bring it down. The usual suspects: wind and/or ice. Often the most vulnerable time is when guy wires are loosened for adjustment or maintenance. (They can stretch over time). Like an out-of-balance propeller, sympathetic vibration can set in.
From the picture with the attached article, the guy wire he hit held long enough to seriously bend the tower. Then the guy either broke, or the aircraft slid off it.
Fixed wing aircraft have no business near a tower. That's why they are marked on aviation sectional maps and lighted with high-power strobes. Nor do helicopters, except when they are used to erect or maintain the tower and antenna.
ahw01
Well-Known Member
The research done for this accident history is really interesting
http://ntsb.gov/_layouts/ntsb.aviation/brief2.aspx?ev_id=20041227X02035&ntsbno=LAX05FA054&akey=1
http://ntsb.gov/_layouts/ntsb.aviation/brief2.aspx?ev_id=20041227X02035&ntsbno=LAX05FA054&akey=1
killbilly
Vocals, Lyrics, Triangle, Washboard, Kittens
There was one around 2200' high near McKinney, TX where I first learned to fly. Sometimes that thing would be poking up out of a low haze and it was ominous as hell, because you KNEW the guy wires were there, you just couldn't see them.
ozziecat35
4 out of 5 great lakes prefer Michigan.
We have a field for my photo survey operation in Iowa south of Iowa City that is very close to a 2000 AGL tower. Normally we are 5500 MSL or higher, but this field is so small we need to be at 2000 MSL to get a good shot, When the tower is above me, I like to give them a WIDE berth.
ctab5060X
Well-Known Member
In normal operations, yes. But if agricultural aircraft avoided every charted obstacle, a fair portion of crops couldn't be treated by air, forcing farmers to go to a less efficient and potentially yield impacting ground rig.
If one recognizes and respects the risks involved, one can safely operate close to any obstacle, whether it be antennas, power lines, buildings, etc...
That being said, seeing the wires on a tower is incredibly difficult when close in an moving fast. Thus why you never look for the wires themselves, you look for other indicators such as the anchor points on the ground. Scout the area; have a game plan. Stay outside of the farthest anchor and you're not going to get tangled up.
RDoug
Well-Known Member
Update — They're taking that tower: A damaged Meteorological Evaluation Tower (MET) in Ruthton has been taken down