MIL-HDBK-274 Electrical Grounding For Aircraft SafetyThis handbook has been prepared to provide U.S. Navy and Marine Corps aircraft maintenance and operations personnel with the background and technical details of the different types of aircraft grounds and how they are applied. In addition, this handbook provides background information for aircraft grounding, static electricity theory and how it affects aircraft, and techniques used for measurement of grounding points. This handbook is intended for use by all U.S. Navy and Marine Corps aircraft maintenance and operations personnel for the purposes of ensuring that aircraft are properly and safely grounded. This handbook is for guidance only and cannot be cited as a requirement.

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4.5.2 Electrical properties of aircraft.  Aircraft in their normal environment have electrical properties similar to resistors and capacitors.  Tires, mooring chains, or static ground straps usually determine the resistance.

4.5.3 Aircraft resistance.  Aircraft resistance is affected by both the resistances of its tires and the runway surface, and by the contact between the tires and the surface.  Tire resistance is a highly variable parameter.  As a tire wears, its resistance increases due to the breaking of the carbon black chains.

4.5.4 Aircraft tire resistance.  The load on the aircraft and the pressure of the tire affect the resistance of the aircraft by affecting the tires' contact with ground.  Increasing tire pressure increases resistance, and increasing load decreases resistance.  Laboratory measurements have indicated tire resistances as high as 3,400 M .

4.5.5 Runway material.  Finally, the material of the runway is a factor in the resistance of the aircraft to the ground.  Dry asphalt has an exceedingly high resistance, while snow and water on surfaces decrease the resistance.  Field measurements have measured total aircraft resistance to ground as high as 40 M .

4.5.6 Aircraft capacitance.  The capacitance of aircraft was found to be a consistent parameter.  Values of 0.002 to 0.005 µF were measured over a wide range of aircraft types and ground plane materials.

4.5.7 Human body electric parameters.  In addition to the characteristics of the aircraft,

the values of human body electrical parameters are needed.  Values of 500 pF capacitance and 50 to 1,500 ohms resistance are representative values for descriptive/discussion purposes.  The pertinent electrical characteristics are summarized in Table III.

TABLE III.  Electrical parameters.

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