Periodic inspection of the shock mounts is required, and  defective mounts should be replaced with the proper type.  The following factors to observe during the inspection are:  If the mount is too stiff, it may not provide adequate  protection against the shock of landing. If the shock mount is  not stiff enough, it may allow prolonged vibration following  an initial shock. Shock-absorbing materials commonly used in shock  mounts are usually electrical insulators. For this reason,  each electronic unit mounted with shock mounts must be  electrically bonded to a structural member of the aircraft to  provide a current path to ground. This is accomplished by  secure attachment of a tinned copper wire braid from the  component, across the mount, to the aircraft structure as  shown in  Figure 11-159 . Occasional bonding is accomplished  with solid aluminum or copper material where a short flexible  strap is not possible. and reliability of avionics components. Rotating electrical  devices, switching devices, ignition systems, propeller  control systems, AC power lines, and voltage regulators  all produce potential damaging fields. Shielding wires to  electric components and ignition systems dissipates radio  frequency noise energy. Instead of radiating into space, the  braided conductive shielding guides unwanted current flows  to ground. To prevent the build-up of electrical potential, all  electrical components should also be bonded to the aircraft  structure (ground). Isolation is another practical method of radio frequency  suppression to prevent interference. This involves separating  the source of the noise from the input circuits of the affected  equipment. In some cases, noise in a receiver may be entirely  eliminated simply by moving the antenna lead-in wire just  a few inches away from a noise source. On other occasions,  when shielding and isolation are not effective, a filter may need  to be installed in the input circuit of an affected component. The aircraft surface can become highly charged with static  electricity while in flight. Measures are required to eliminate  the build-up and radiation of unwanted electrical charges.  One of the most important measures taken to eliminate  unwanted electrical charges which may damage or interfere  with avionics equipment is bonding. Charges flowing in  paths of variable resistance due to such causes as intermittent  contact from vibration or the movement of a control surface  produce electrical disturbances (noise) in avionics. Bonding  provides the necessary electric connection between metallic  parts of an aircraft to prevent variable resistance in the  airframe. It provides a low-impedance ground return which  minimizes interference from static electricity charges. Suppression of unwanted electromagnetic fields and  electrostatic interference is essential on all aircraft. In  communication radios, this is noticeable as audible noise.  In other components, the effects may not be audible but  pose a threat to proper operation. Large discharges of static  electricity can permanently damage the sensitive solid-state  microelectronics found in nearly all modern avionics. Many components of an aircraft are possible sources of  electrical interference which can deteriorate the performance  All metal parts of the aircraft should be bonded to prevent  the development of electrical potential build-up. Bonding  also provides the low resistance return path for single- wire electrical systems. Bonding jumpers and clamps are  examples of bonding connectors. Jumpers should be as short  as possible. Be sure finishes are removed in the contact area  of a bonding device so that metal-to-metal contact exists.  Resistance should not exceed .003 ohm. When a jumper  is used only to reduce radio frequency noise and is not  for current carrying purposes, a resistance of 0.01 ohm is  satisfactory.  Static dischargers, or wicks, are installed on aircraft to  reduce radio receiver interference. This interference is  caused by corona discharge emitted from the aircraft as a  result of precipitation static. Corona occurs in short pulses  11-74 Figure 11-159.  A bonding jumper is used to ground an equipment  rack and avionics chassis around the non-conductive shock mount  material.  Static Discharge Wicks Shielding  Reducing Radio Interference Bonding  Isolation 3.  Overall rigidity of the mount.  2.  Stiffness and resiliency of the material; and  1.  Deterioration of the shock-absorbing material;  Bonding jumper Shock mount