mile) distant object will allow a comparison of points within a 73 meter (240 foot) width, or
effectively, the whole CCP site. If the magnetic declinations of the different points vary by more than
12 minutes (12') of arc, then the site is not magnetically quiet.
A11.4.3. Reciprocal Observation Method. Several scattered points are selected and marked in the area
to be tested. The transit will be set up over one central point and the magnetic azimuth to all of the
other points will be determined and recorded. Then the transit will be set up over all the other points
and a back azimuth to the central point will be determined and recorded. If there are no magnetic
disturbances, then the original azimuth and the back azimuth should be the same for each of the points
checked. If there is a difference between the azimuth and back azimuth of any of the points, which is
greater than 12 minutes (12') of arc, then the site is not magnetically quiet.
A11.5. Magnetic Survey Requirements. The magnetic survey for the CCP is an airfield engineering
survey. AR 95-2 requires that airfield engineering surveys be scheduled on recurring five-year cycles.
(The Navy and Marine Corps require annual engineering surveys). This cycle is operationally important,
since magnetic north not only varies at different locations on the earth, but it also physically changes as a
function of time. It is an operational requirement to calibrate aircrafts' compass correction factors on a
regular basis because of these changes. Additionally, the magnetic survey assures that the aircraft will be
in a "magnetically quiet zone" which is essential to assure proper calibration of its compass. The magnetic
survey for the compass calibration pads must be performed in accordance with paragraph A11.5.
A11.6. Magnetic Survey Procedures. These procedures consist of the magnetic field survey which is
used to determine the magnetic declination of a site and the magnetic direction survey which is used to
layout the CCP markings. Both a magnetic field survey and a magnetic direction survey of the CCP will
be performed every five years or sooner as required by the controlling agency and when magnetic
influences have occurred within or adjacent to the CCP. Magnetic influences are considered to be
additions of power lines, installation of items containing ferrous metals, or similar activities within an
influencing distance of the CCP as defined in paragraph A11.6.
A11.6.1. Magnetic Field Survey (Variation Check). This survey is to measure the magnetic
declination within the CCP area. The surveyor will be required to certify that the variations of the
magnetic field are within the allowable range and to provide the average magnetic declination of the
area. The direction of the horizontal component of the Earth's magnetic field (magnetic declination)
measured at any point within a space between 0.6 meters (2 feet) and 1.8 meters (6 feet) above the
surface of the CCP, and extending over the entire area of the CCP, must not differ by more than 12
minutes (12') of arc from the direction measured at any other point within this area. All raw data,
intermediate computations, and final results will be submitted in a clear, neat, and concise format. The
surveyor will accurately layout a 6 meter by 6 meter (20 foot by 20 foot) grid with its center point
coincident with the center point of the CCP. The grid will be laid out so the entire area of the CCP plus
a minimum of 6 meters (20 feet) outside each edge of the CCP is covered. The grid may be laid out in
any direction, but a true north or a magnetic north direction is preferred, since it will simplify the
azimuth calculations and allow immediate recognition of points that are outside the allowable
declination limits. In any case, the surveyor will have to determine the true azimuth of the grid layout
by standard surveying procedures so the azimuth and declination of each point can be determined.
After the grid is laid out, the surveyor will check the declination of all the grid points by one of the
following methods:
A11.6.1.1. Distant Object Method. A distant landmark is selected for siting from the various
points of the area being checked. A second distant object at approximately 90 degrees (90) can
also be chosen to increase accuracy. The further away the distant object is, the wider an area of
points that can be compared to each other and still obtain the accuracy needed. An 8 kilometer (5
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