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

4.  GENERAL GUIDANCE

4.1 Theoretical basis for aircraft grounding. This section provides theory, background, and information necessary to understand the rationale behind the guidelines for aircraft grounding and bonding.  Theory and equations associated with both electrostatic charge generation in aircraft and grounding effects are discussed.  This section also includes guidance related to triboelectric effects, fuel flow, induced charge, and friction.  Hazards from ground power faults, RF energy, and lightning are presented.  Descriptions of aircraft electrical parameters and a discussion of hazardous thresholds and the possible dangers they present to personnel and aircraft safety are present.  The section also illustrates how proper grounding will reduce these hazards.

4.2 Electrostatic theory. Electrostatic theory is the study of accumulated electrical

charges.  Potential differences between these charges may measure thousands of volts.  However, the flow of electricity during generation and accumulation is small, on the order of thousandths

or millionths of an ampere (A).  A primary manifestation of static electricity is the discharge or sparking of the accumulated charges.  Static electricity charges are generated by the separation of like and unlike bodies.   These charges become evident when the unlike bodies, having been in contact with each other, are separated.  For significant potential to be developed, the bodies holding the charges will become, and remain, insulated from each other.  Insulation may occur through complete physical separation of the bodies or because at least one of the bodies is an insulator.

4.3 Scenarios. Aircraft maintenance and ordnance handling evolutions are considered in this manual.  Potential hazards considered during each scenario are:

a. Static electrical shock to personnel b. Ordnance actuation or malfunction

c. Uncommanded ordnance or stores release d. Damage or upset to electronic subsystems

4.4 Energy sources.  Evaluation of a situation's potential hazards is based on the source mechanism and the source magnitude of the electrical energy.  With operations involving aircraft such as stores handling, maintenance, fueling, and aircraft parking, the following energy sources need to be considered:

a. Static

(1) Triboelectric

(2) Induced Static Charge

(3) Friction

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