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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MIL-HDBK-274A

FIGURE 1.  Cloud-inducing charge on aircraft.

4.4.1.2.1 Potential hazard. The situation becomes a potential hazard if a sudden change in the electric field takes place (for example, a distant lightning strike discharging the overhead cloud).  The Earth's surface neutralizes more quickly than the ungrounded aircraft (due to the capacitance of the aircraft and the high resistance of the tires), resulting in potentials up to 60 kV from airframe to ground.  A person in contact with the aircraft during this change in the electrical field acts as a resistor connected to ground, facilitating another path to ground for the accumulated charges (see Figure 2). This person will probably feel a sharp shock, the severity

of which will depend on the extent to which the aircraft was originally charged.  The current shock can result in injury to personnel in two different ways:

a. Reflex movements. The current shock can cause involuntary reflex movements that can cause fatal or serious injury due to secondary effects, such as falling.

injury.

b. Electrical effects.  The current shock can cause electrical effects that result directly in

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