antenna leads, etc. is also an important part of the installation  process. When selecting a location for the equipment, use  the area(s) designated by the airframe manufacturer or the  STC. If such information is not available, select a location for  installation that will carry the loads imposed by the weight  of the equipment, and which is capable of withstanding the  additional inertia forces. If an avionics device is to be mounted in the instrument panel  and no provisions have been made for such an installation,  ensure that the panel is not a primary structure prior to making  any cutouts. To minimize the load on a stationary instrument  panel, a support bracket may be installed between the rear of  the electronics case or rack and a nearby structural member  of the aircraft.  [Figure 11-157] Avionics radio equipment must be securely mounted to the  aircraft. All mounting bolts must be secured by locking devices  to prevent loosening from vibration. Adequate clearance  between all units and adjacent structure must be provided to  prevent mechanical damage to electric wiring or to the avionic  equipment from vibration, chafing, or landing shock. When adding a unit to an aircraft, the installation should  be planned so that it can dissipate heat readily. In some  installations, it may be necessary to produce airflow over  the new equipment either with a blower or through the use  of routed ram air. Be sure that proper baffling is used to  prevent water from reaching any electronics when ducting  outside air. The presence of water in avionics equipment areas  promotes rapid deterioration of the exposed components and  could lead to failure. Vibration is a continued motion by an oscillating force. The  amplitude and frequency of vibration of the aircraft structure  will vary considerably with the type of aircraft. Avionics  equipment is sensitive to mechanical shock and vibration  and is normally shock mounted to provide some protection  against in-flight vibration and landing shock. Special shock mounted racks are often used to isolate avionics  equipment from vibrating structure.  [Figure 11-158]  Such  mounts should provide adequate isolation over the entire  range of expected vibration frequencies. When installing  shock mounts, assure that the equipment weight does not  exceed the weight-carrying capabilities of the mounts. Radio  equipment installed on shock mounts must have sufficient  clearance from surrounding equipment and structure to allow  for normal swaying of the equipment. Do not locate avionics equipment and wiring near  units containing combustible fluids. When separation is  impractical, install baffles or shrouds to prevent contact of  the combustible fluids with any electronic equipment in the  event of plumbing failure. The performance and service life of most avionics equipment  is seriously limited by excessive ambient temperatures. High  performance aircraft with avionics equipment racks typically  route air-conditioned air over the avionics to keep them cool.  It is also common for non-air conditioned aircraft to use a  blower or scooped ram air to cool avionics installations.  Radios installed in instrument panels do not ordinarily require  vibration protection since the panel itself is usually shock  mounted. However, make certain that the added weight of any  added equipment can be safely carried by the existing mounts.  In some cases, it may be necessary to install larger capacity  mounts or to increase the number of mounting points. Cooling and Moisture  Vibration Isolation 11-73 Figure 11-158.  A shock mounted equipment rack is often used to  install avionics.  Figure 11-157.  An avionics installation in a stationary instrument  panel may include a support for the avionics case. Machine screws and self-locking nuts Rear case support Rivets or machine screws and self-locking nuts Shock mount