MIL-HDBK-274A
4.4.2.3.2 RF energy protection. Since there is limited protection from transmitted RF energy, it is necessary that personnel ensure that no operations are conducted without observation of all recommended procedures. For instance, a fuel hose nozzle should always
be bonded to the aircraft before the filling cap is removed and the hose nozzle inserted into the fuel tank. Conversely, the filling cap should be replaced before the bond is disconnected from the aircraft. These procedures will ensure that no RF arcs are inadvertently produced in a hazardous atmosphere while the fuel tank cap is removed.
4.4.2.3.3 Induced RF energy. Naval aircraft encounter high powered communication and radar transmitters in their operating environments. Of most concern are those which may be located near parked aircraft, for example, on the carrier flight deck, which probably contains the highest concentration of transmitted RF energy to be found on any aircraft operating base. Transmitters onboard adjacent aircraft may have interfering effects also. The principal problem is the amount of RF energy that is induced into the aircraft frame and circulating on the aircraft skin. This quantity or level of RF energy is greatly affected by the position of the aircraft
relative to a particular RF transmitter, the power output of that transmitter, and the actual frequency of the RF energy being transmitted. It is further affected by the actual location of any connections between the aircraft and ground (deck). Where the position of one ground may have a significant effect on the induced currents, other ground connections from different locations on the aircraft to other locations on the deck may not have the same effect. Any existing aircraft grounding scheme should not be altered in an effort to provide the aircraft with additional protection against RF energy. If the ground connection is broken while the RF transmission is in progress, an electric arc may be drawn. This is an important fact to note. If an arc is produced while disconnecting a ground, the source may be RF energy, caused by a local transmitter and
the current flow can be high. A power line short circuit to ground may also produce an arc when the ground is disconnected. Additional guidance on electromagnetic energy effects can be found in MIL-HDBK-235-1 and MIL-STD-464.
4.4.2.3.4 RF arcing. RF arcing is not limited to aircraft. In high RF fields, arcs generally occur at the discontinuities in conductors (conductor meaning any metal surface). A discontinuity is any place where the nature of the conductor changes. Examples include gaps between metal surfaces and places where the type of metal changes or the thickness of the metal changes. Another factor that has an influence on the occurrence of RF arcing is the actual physical dimensions of the metal surface. Not all conductors within an RF field are susceptible to arcing at their discontinuities. Objects that are large with respect to a wavelength (several
wavelengths in each direction perpendicular to the line of transmission) tend to reflect RF energy and are less apt to produce arcing. Objects that are long in one dimension but not in the other tend to be a more favorable site for arcing.
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