Warning! Radar operating

Warning! Radar Operating By Jim Sparks May-June 1998 The primary purpose of weather radar is to detect storms along the flight path and give the pilot a visual indication of rainfall intensity, and with doppler radar, possible turbulence...


Both physical and electrical thickness are important factors in the design of a radome. Electrical thickness is related to physical thickness and is based on mathematical equations that factor in operating frequencies, materials used, and the type of construction. A very small variation in physical thickness can have a major effect on electrical thickness. For this reason radomes are fabricated for specific types of radar. If a radome designed for a "C" band radar was installed on an aircraft using "X" band, the performance will be degraded. Paint or other coatings such as abrasion shields need to be of a material that will not interfere with the transmitted signal and cannot be an excessive thickness.

Electrical bonding is another area of genuine concern. Airframe manufacturers typically have detailed procedures for maintenance and repair while frequent inspections are an excellent way to prevent radar discrepancies. When viewing, always check for cracks, erosion, delamination and condition of the "static strips." Anytime a radome is repaired or is a suspect in causing poorly operating radar, several tests should be conducted. These include "transmissivity," which is the ability of a radome to pass radar energy, "reflection," which is the amount of returned energy that did not pass through the radome back into the antenna, and "diffraction," which is the bending of the radar wave as it goes through the structure.

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When any of these electrical properties are not within prescribed tolerances, signal loss will occur. The targets may become cluttered and distorted.

The most frequent damage to radomes are holes caused by electrostatic discharge. Regardless of size, these holes can cause significant damage by allowing moisture in. Structural damage will result when a quantity of trapped moisture freezes within the walls of the radome and causes delamination. The accumulation of water can also cause a reflection of radar energy that may result in a radar image displayed to the flight crew where nothing really exists. Electrostatic bonding tests on radomes are required by most aircraft manufactures. These checks should also be done anytime small discharge holes are revealed.

Many dangers can result from a radar operating at an inopportune time. With the high voltages and the escape of x-rays that could occur, most radar maintenance is best left to those who are well qualified. Avoid walking or working within the safety zone of an operating radar (usually seven feet). Anytime "power-ON" maintenance is to be performed on a radar-equipped aircraft, take the extra time needed to make sure the system is OFF.

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