Par 702 Page 150
(10) Perform an electrical resistance test as described in Chapter 6, subparagraph 603a(12).
FIGURE 7-1. STUD BONDING OR GROUNDING TO FLAT SURFACE Notes:
*See Table 7-1 for specific materials.
†Limited to a quantity of four (4).
Par 702 Page 151 TABLE 7-1. HARDWARE FOR STUD BONDING OR GROUNDING TO FLAT
SURFACE Structure Screw or Bolt and Lock Nut Plain Nut Washer A Washer B Washer C Lockwasher E Lockwasher F
ALUMINUM TERMINALS AND JUMPER Aluminum Alloys Cadmium- Plated Steel Cadmium- Plated Steel Aluminum Alloy Aluminum Alloy Cadmium- Plated Steel or Aluminum Cadmium- Plated Steel Cadmium- Plated Steel Magnesium Alloys Cadmium- Plated Steel Cadmium- Plated Steel Magnesium Alloy* Magnesium Alloy* Cadmium- Plated Steel or Aluminum Cadmium- Plated Steel Cadmium- Plated Steel Steel, Cadmium- Plated Cadmium- Plated Steel Cadmium- Plated Steel None None Cadmium- Plated Steel or Aluminum Cadmium- Plated Steel Cadmium- Plated Steel Steel, Corrosion- Resistant Corrosion- Resistant Steel Cadmium- Plated Steel None None Cadmium- Plated Steel or Aluminum Corrosion- Resistant Steel Cadmium- Plated Steel
TINNED COPPER TERMINALS AND JUMPER Aluminum Alloys Cadmium- Plated Steel Cadmium- Plated Steel Aluminum Alloy Aluminum Alloy Cadmium- Plated Steel Cadmium- Plated Steel Cadmium- Plated Steel or Aluminum Magnesium Alloys Caution: Do not connect copper to magnesium Steel, Cadmium- Plated Cadmium- Plated Steel Cadmium- Plated Steel None None Cadmium- Plated Steel Cadmium- Plated Steel Cadmium- Plated Steel Steel, Corrosion- Resistant Corrosion- Resistant Steel Cadmium- Plated Steel None None Cadmium- Plated Steel Corrosion- Resistant Steel Corrosion- Resistant Steel *When not available, use aluminum alloy.
Par 702 Page 152 FIGURE 7-2. NUT PLATE BONDING OR GROUNDING TO FLAT SURFACE Notes:
*See Table 7-2 for specific materials.
†Limited to a quantity of four (4).
Par 702 Page 153 TABLE 7-2. HARDWARE FOR NUT PLATE BONDING OR GROUNDING TO FLAT
SURFACE Structure Screw or Bolt and Nut Plate Rivet Lockwasher Washer A Washer B
ALUMINUM TERMINALS AND JUMPER Aluminum Alloys Cadmium-Plated Steel Aluminum Alloy Cadmium- Plated Steel Cadmium-Plated Steel Aluminum Alloy Magnesium Alloys Cadmium-Plated Steel Aluminum Alloy Cadmium- Plated Steel Cadmium-Plated Steel Magnesium* Alloy Steel, Cadmium-Plated Cadmium-Plated Steel Corrosion- Resistant Steel Cadmium- Plated Steel Cadmium-Plated Steel Aluminum Alloy Steel, Corrosion- Resistant Corrosion- Resistant Steel Corrosion- Resistant Steel Cadmium- Plated Steel Cadmium-Plated Steel or Aluminum Alloy Cadmium-Plated Steel
TINNED COPPER TERMINALS AND JUMPER Aluminum Alloys Cadmium-Plated Steel Aluminum Alloy Cadmium- Plated Steel Cadmium-Plated Steel Aluminum Alloy Magnesium Alloys Caution: Do not connect copper to magnesium Steel, Cadmium-Plated Cadmium-Plated Steel Corrosion- Resistant Steel Cadmium- Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Steel, Corrosion- Resistant Corrosion- Resistant Steel Corrosion- Resistant Steel Cadmium- Plated Steel Cadmium-Plated Steel Corrosion- Plated Steel or Corrosion- Resistant Steel *When not available, use aluminum alloy.
Par 702 Page 154 FIGURE 7-3. BOLT AND NUT BONDING OR GROUNDING No tes:
*See Table 7-3 for specific materials.
†Limited to a quantity of four (4).
Par 702 Page 155 FIGURE 7-4. COPPER JUMPER CONNECTOR TO TUBULAR STRUCTURE Notes:
*Inside surface of clamp (conduit) is cylindrical.
Par 702 Page 156 TABLE 7-3. HARDWARE FOR BOLT-AND-NUT Structure Screw or Bolt and Nut Plate Rivet Lockwasher Washer A Washer B
ALUMINUM TERMINALS AND JUMPER Aluminum Alloys Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel or Aluminum Alloy None Cadmium-Plated Steel or Aluminum Alloy Magnesium Alloys Cadmium-Plated Steel Chromium- Plated Steel Magnesium Alloys Magnesium* Alloys Cadmium-Plated Steel or Aluminum Alloy Steel, Cadmium-Plated Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel* Steel, Corrosion- Resistant Corrosion- Resistant Steel Corrosion- Resistant Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel
TINNED COPPER TERMINALS AND JUMPER Aluminum Alloys Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Aluminum Alloy Cadmium-Plated Steel Magnesium Alloys Caution: Do not connect copper to magnesium Steel, Cadmium-Plated Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Steel, Corrosion- Resistant Corrosion- Resistant Steel or Cadmium- Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel or Corrosion- Resistant Steel *When not available, use aluminum alloy.
FIGURE 7-5. BONDING CONDUIT TO STRUCTURE
CADMIUM PLATED AN 735 CLAMP* STEEL SCREW ALUMINUM WASHER
STRUCTURE
- ALUMINUM WASHER
CADMIUM PLATED
STEEL LOCKWASHER
CADMIUM PLATED
STEEL LOCKNUT NOTE: Aluminum alloy or corrosion-resistant steel conduit (inside surface).
FIGURE 7-6. ALUMINUM JUMPER CONNECTOR TO TUBULAR STRUCTURE
CADMUIM PLATED
STEEL SCREW AN 735 CLAMP* ALUMINUM WASHER
ALUMINUM TERMINAL
ALUMINUM WASHER
CADMIUM PLATED
STEEL LOCKWASHER
CADMIUM PLATED
STEEL LOCKNUT NOTE: Inside surface of clamp (conduit) is cylindrical.
Par 702 Page 157
Par 702 Page 158
b. Preservation. Preservation provides a nonconductive film to protect the bonding or grounding connection from corrosion by excluding moisture. Three preservation methods are discussed. See Chapter 4, paragraph 407, and Table 4-4 for more information.
(1) This application is intended for bonding or grounding connections that require protection for up to a year when the connection is covered and protected from the outside environment. Apply a thin film of Water-Displacing Corrosion Preventive Compound to the bonding or grounding connection, conforming to MIL-DTL-85054.
(2) This application is intended for bonding or grounding connections that may require fairly frequent disassembly. Apply a thin film of Water-Displacing Corrosion Preventive Compound to the bonding or grounding connection, conforming to MIL-PRF-81309, Type III, followed by a coating of Corrosion Preventive Compound, conforming to MIL-PRF-16173, Grade 4.
(3) This application is intended for bonding or grounding connections that seldom require disassembly. Using a spatula and Sealing Compound Type II, fully encapsulate the bonding or grounding connection, conforming to MIL-PRF-81733.
c. Electronic Equipment Shock Mount Bonding and Preservation. This type of electrical bonding uses a bonding wire (jumper assembly) or strips of aluminum or copper. The following corrosion prevention method applies:
(1) Clean base of shock mount and bonding wire (jumper assembly) or strips of aluminum or copper by wiping with a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow components to air dry.
(2) After assembly of the shock mount and bonding wire (jumper assembly) or strips of aluminum or copper, apply a thin film of Water-Displacing Corrosion Preventive Compound over the shock mount and jumper assembly attach area, conforming to MIL-PRF-81309, Type II.
For protection of up to a year and for shock mount and bonding wire assemblies that do not require frequent disassembly, apply an additional coat of Water-Displacing Corrosion Preventive Compound over the shock mount and jumper assembly attach area, conforming to MIL-DTL-85054.
703 through 800. RESERVED.
Par 801 Page 159 CHAPTER 8. EFFECT AND TREATMENT OF CORROSION ON
ELECTROMAGNETIC INTERFERENCE SHIELDING DEVICES
801. DEFINITION/DESCRIPTION OF ELECTROMAGNETIC INTERFERENCE (EMI).
a. EMI is the presence of undesirable voltages or currents which appear in a circuit as a result of the operation of another electrical source. EMI includes effects from lightning, external radiated radio frequency (RF) fields, or conducted and radiated electromagnetic interference between systems in the aircraft. In this section, the term EMI will include all of these effects.
Some examples of EMI-related aircraft system malfunctions are microprocessor bit errors, computer memory loss, audio tones on communication systems, and false indications
(i.e., alarms, lights, readouts, or power loss). The results of such malfunctions can severely impact system or subsystem operation. EMI may be radiated or conducted. Typical sources of radiated emissions are radio and radar transmitters, power supplies, generators, and transformers.
The way in which external EMI intrudes into a circuit is called the coupling mode. Radiated EMI propagates through the air from the source to the victim circuit. An antenna, or a cable which acts as an antenna, couples the EMI to the victim circuit. Conducted EMI is coupled from the source to the victim circuit between common connections, either wiring or metallic structure.
b. Due to the increase in electronic systems installed in modern aircraft, the importance of many of these systems for flight safety, and the decrease in power levels required to upset them, EMI, lightning, and high intensity radiated field (HIRF) protection has become an essential part of aircraft design. The use of electrical and electronic systems for full-authority aircraft flight and engine controls has been a significant factor in increasing the importance of aircraft EMI protection. The aircraft system EMI protection will involve the structure around the system, wire routing, shields over the wires, shield terminations, filters inside and outside the equipment, circuit and equipment grounding, and circuit design. Most of these protection features rely upon low-resistance and low-impedance electrical bonds for wires, shields and structure, which often include dissimilar metals. For this reason, an understanding of the purpose of these devices, where they may be located, and corrosion-control processes are necessary knowledge for the aircraft maintainer.
802. EMI STANDARDS, TEST REQUIREMENTS, AND DOCUMENTS. Electronic components are designed to various specifications, depending on their application and the electromagnetic environments in which they are expected to operate. Most specifications include susceptibility requirements, the level of EMI in which the device is expected to operate successfully, and emission requirements, the limits of EMI that the device may generate. Aircraft and systems manufacturers may have their own EMI standards and requirements, but they are based on the following:
a. RTCA DO-160, Environmental Conditions and Test Procedures for Airborne Equipment.
b. AC 20-136, Protection of Aircraft Electrical/Electronic Systems Against the Indirect Effects of Lightning.
Par 802 Page 160
c. AC 20-53, Protection of Aircraft Fuel Systems Against Fuel Vapor Ignition Caused by Lightning.
d. DOT/FAA/CT-83/3, User’s Manual for AC 20-53A, Protection of Airplane Fuel Systems Against Fuel Vapor Ignition Due to Lightning.
e. AC 20-158, The Certification of Aircraft Electrical and Electronic Systems for Operation in the High-Intensity Radiated Fields (HIRF) Environment.
f. MIL-STD-464, Electromagnetic Environmental Effects Requirements for Systems.
g. MIL-HDBK-235, Military Operational Electromagnetic Environment Profiles.
h. DOT/FAA/CT-86/40, Aircraft Electromagnetic Compatibility.
803. AIRCRAFT SYSTEM EMI PROTECTION REQUIREMENTS. Although electronic and electrical equipment are usually tested individually for lightning, HIRF, radiated and conducted EMI, and EMI susceptibility and emissions, aircraft manufacturers should still ensure that the integrated electronic systems on the aircraft will operate successfully in the electromagnetic environment to which the aircraft will be exposed. Figure 8-1 and the following paragraphs describe some of the aircraft-specific EMI issues that should be addressed.
a. Intrasystem EMI Requirements. Intrasystem EMI refers to electrical or electronic subsystems within an aircraft interfering with one another. Even subsystems designed to similar emission and susceptibility requirements may have EMI problems when integrated in an aircraft.
This may be due to the location of the equipment on the aircraft, frequencies involved, cable routing, or bonding and grounding techniques. All of these factors should be addressed by the aircraft manufacturer in order to ensure a compatible design. In a worst-case situation, when intrasystem EMI cannot be avoided, operation of one system may not be possible while another is operating. Changes to electronic systems or installation of new systems can impact intrasystem electromagnetic compatibility (EMC) as well.
b. Intersystem EMI Requirements. Intersystem EMI refers to electrical or electronic systems external to the aircraft interfering with aircraft systems. These external systems emit various frequencies and power levels which are not always easily predictable. Protection from intersystem EMI can include various types of shielding for aircraft openings and wiring.
Par 803 Page 161 FIGURE 8-1. TYPES OF ELECTROMAGNETIC INTERFERENCE
c. L ightning.
(1) Effects of Lightning Strikes. The effects of lightning strikes on aircraft may be classified as either direct or indirect. The direct effects are largely structural. They are the burning, eroding, blasting, and structural deformation caused by lightning arc attachment, high pressure shock waves, and magnetic forces produced by the associated high currents. Indirect effects predominantly result from the interaction of lightning fields and currents with electrical equipment or wiring. Fuel ignition may result from either direct arc ignition, or indirect effects creating arcs or sparks. For the purpose of studying lightning effects, aircraft are typically divided into three major lightning attachment zones: direct attachment, swept stroke, and conducted currents or transfer. Testing with simulated high voltage strikes on aircraft scale models using various aspect angles can provide confidence in zone assignment. Zone 1 (direct attachment) includes areas where lightning current enters or exits the aircraft. Zone 2 (swept stroke) includes areas directly behind the direct attach points where the established ionized lightning channel is swept back over the aircraft surface as it flies through or away from the channel. Zone 3 (current transfer) includes areas where there is a low probability of direct