Par 11-272 Page 11-592 TABLE 11-27. Electronic/Electrical Symbols (continued).
Symbol Meaning
Selector or Multiposition Switch
Safety Interlock
Limit Switch Sensitive Switch
Switches with Time-Delay Feature
Flow-Actuated Switch
Par 11-272 Page 11-593 TABLE 11-27. Electronic/Electrical Symbols (continued).
Symbol Meaning
Liquid-Level Actuated Switch
Pressure- or Vacuum-Actuated Switch
Temperature-Actuated Switch
Thermostat
Flasher Self-Interrupting Switch
Foot-Operated Switch Foot Switch
Switch Operated by Shaft Rotation and Responsive to Speed or Direction
Switches with Specific Features
Par 11-272 Page 11-594 TABLE 11-27. Electronic/Electrical Symbols (continued).
Symbol Meaning
Governor Speed Regulator
Relay
Inertia Switch
Mercur Switch
Terminals
Par 11-272 Page 11-595 TABLE 11-27. Electronic/Electrical Symbols (continued).
Symbol Meaning
Cable Termination
Connector Disconnecting Device
Connectors of the Type Commonly Used for Power-Supply Purposes
Test Blocks
Coaxial Connector
Waveguide Flanges Waveguide Junction
Par 11-272 Page 11-596 TABLE 11-27. Electronic/Electrical Symbols (continued).
Symbol Meaning
Fuse
Lightning Arrester Arrester Gap
Circuit Breaker
Protective Relay
Audible-Signaling Device
Microphone
Par 11-272 Page 11-597 TABLE 11-27. Electronic/Electrical Symbols (continued).
Symbol Meaning
Handset Operator’s Set
Lamp
Visual-Signaling Device
Mechanical Connection Mechanical Interlock
Mechanical Motion
Clutch Brake
Par 12-1 Page 12-598 (and 12-2) TABLE 11-27. Electronic/Electrical Symbols (continued).
Symbol Meaning
Manual Control
Gyro Gyroscope Gyrocompass
Position Indicator
Fire Extinguisher Actuator Head
Position Transmitter
Radio Station
Space Station
Integrated Circuit Amplifiers
GENERAL SYMBOLS MAGNETIC AMPLIFIER
INVERTOR OR
NOT GATE Logic Gates
AND GATE WITH THREE INPUTS NAND (NOT AND) GATE
OR GATE NOR (NOT OR) GATE
EXCLUSIVE OR GATE Diode
EMITTER BASE COLLECTOR Transistor Symbols
EMITTER BASE COLLECTOR E- - C E B
11-273.11-283. [RESERVED.] Par 12-1 Page 12-599 (and 12-2)
Par 12-1 Page 12-600 (and 12-2) CHAPTER 12. AIRCRAFT AVIONICS SYSTEMS
SECTION 1. AVIONICS EQUIPMENT MAINTENANCE
GENERAL. There are several methods of ground checking avionics systems.
Visual Check. Check for physical condition and safety of equipment and components.
Operation Check. This check is performed primary by the pilot, but may also be performed by the mechanics after annual and 100-hour inspections. The aircraft flight manual, the Airman’s Information Manual (AIM), and the manufacturer’s information are used as a reference when performing the check.
Functional Test. This is performed by qualified mechanics and repair stati ons to check the calibration and accuracy of the avionics with the use of test equipment while they are still on the aircraft, such as the transponder and the static checks. The equipment manufacturer’s manuals and procedures are used as a reference.
Bench Test . When using this method the unit or instrument is removed from the aircraft and inspected, repaired, and calibrated as required.
Electromagnetic Interference (EMI). For EMI tests, refer to chapter 11 paragraph 11-107 of this AC.
HANDLING OF COMPONENTS. Any unit containing electronic components such as transistors, diodes, integrated circuits, proms, roms, and memory devices should be protected from excessive shocks. Excessive shock can cause internal failures in an of these components. Most electronic devices are subject to damage by electrostatic discharges (ESD).
CAUTION: To prevent damage due to excessive electrostatic discharge, proper gloves, finger cots, or grounding bracelets should be used. Observe the standard procedures for handling equipment containing electrostatic sensitive devices or assemblies in accordance with the recommendations and procedures set forth in the maintenance instructions set forth by the equipment manufacturers.
12-3.12-7. [RESERVED.]
Par 12-8 Page 12-601
SECTION 2. GROUND OPERATIONAL CHECKS FOR AVIONICS
EQUIPMENT (ELECTRICAL)
GENERAL. When the operating or airworthiness regulations require a system to perform its intended function, the use of the Technical Standard Order (TSO) equipment or the submission of data substantiating the equipment performance is strongly recommended. An operation check of avionics is the responsibility of the pilot in command.
However, it is recommended that after replacement of equipment during 100 hour or annual inspections, an operational check of avionics equipment be performed. The accomplishments of these checks must be done in accordance with the recommendations and procedures set forth in the aircraft’s flight manual instructions published by the avionics equipment manufacturers.
INSPECTION OF AVIONICS SYSTEMS.
The inspection shall include the following:
Inspect the condition and security of equipment including the proper security of wiring bundles.
Check for indications of overheating of the equipment and associated wiring.
Check for poor electrical bonding. The bonding requirements are specified by equipment manufacturers. Installation cabling should be kept as short as possible, except for antenna cables which are usually precut or have a specific length called out at installation.
Proper bonding on the order of 0.003 ohms is very important to the performance of avionics equipment.
Check to assure that the radios and instruments are secured to the instrument panel.
Check that all avionics are free of dust, dirt, lint, or any other airborne contaminates. If there is a forced air cooling system, it must be inspected for proper operation. Equipment ventilation openings must not be obstructed.
Check the microphone headset plugs and connectors and all switches and controls for condition and operation. Check all avionics instruments for placards. Check lightening, annunciator lights, and cockpit interphone for proper operation.
The circuit breaker panel must be inspected for the presence of placarding for each circuit breaker installed.
Check the electrical circuit switches, especially the spring-load type for proper operation. An internal failure in this type of switch may allow the switch to remain closed even though the toggle or button returns to the OFF position. During inspection, attention must be given to the possibility that improper switch substitution may have been made.
Check antennas for:
broken or missing antenna insulators
lead through insulators
springs
Par 12-12 Page 12-602 safety wires
cracked antenna housings
missing or poor sealant at base of antenna
correct installation
signs of corrosion, and
the condition of paint/bonding and grounding.
Check the bonding of each antenna from mounting base to the aircraft skin. Tolerance:
.1 ohm, maximum.
Test Equipment:
1502B Metallic Time Do Main Reflectometer or equivalent.
Thruline Wattmeter.
Perform the antenna evaluation check using the domain reflectometer to determine the condition of the antenna and coax cables.
Refer to manufacturer’s maintenance procedures.
Use thruline wattmeter as needed for addition evaluation. Refer to manufacturer’s maintenance procedures.
Check for the following:
Resistance.
Shorts.
Opens.
Check the static dischargers/wicks for:
physical security of mounting attachments, wear or abrasion of wicks, missing wicks, etc.,
assurance that one inch of the inner braid of flexible vinyl cover wicks extends beyond the vinyl covering,
assurance that all dischargers are present and securely mounted to their base,
assurance that all bases are securely bonded to skin of aircraft, in order to prevent the existence in voltage level differences between two surfaces,
signs of excessive erosion or deterioration of discharger tip,
lighting damage as evidenced by pitting of the metal base, and
megohm value of static wick itself as per manufacturer’s instructions. It should not be open.
Subsequent inspection must be made after a maintenance action on a transponder. Refer to Title 14 of the Code of Federal Regulations (14 CFR) part 91, sections 91.411 and 91.413.
Inspection of the emergency locator transmitter operation, condition and date of the battery.
Perform a function check of the radio by transmitting a request for a radio check. Perform a function check on navigation equipment by moving the omni bearing selection (OBS) and noting the needle swing; and the TO/FROM flag movement.
Par 12-10 Page 12-603 COMMUNICATION SYSTEMS. Ground operation of communication systems in aircraft may be accomplished in accordance with the procedures appropriate for the airport and area in which the test is made, and the manufacturer’s manuals and procedures.
Check system(s) for side tone, clarity of transmission, squelch, operations using head phones, speaker(s), and hand microphone. If a receiver or transmitter is found to be defective, it should be removed from the aircraft and repaired.
VHF OMNI-DIRECTIONAL RANGE (VOR). A VOR operates within the
108.0 to 117.9 MHz frequency band. The display usually consists of a deviation indicator and a TO/FROM indicator. The controls consist of a frequency selector for selecting the ground station and an OBS, which is used for course selection. An ON/OFF flag is used to determine adequate field strength and presence of a valid signal. There are numerous configurations when integrated into flight directors and/or when usi ng a slaved compass system which uses an additional indicator that points continually to the selected omni station regardless of OBS selection. In order to determine the accuracy specified in a functional check, a ground test set must be used in accordance w ith the manufacturer’s specifications. For the purpose of this inspection/maintenance activity, the following operational check can be accomplished to determine if the equipment has the accuracy required for operation in instrument flight rules (IFR) environment. Verify audio identification, OBS operation, flag operation, radio magnetic indicator (RMI) in terface, and applicable navigation (NAV) switching functions. The operational check is also published in the AIM, section 1-1-4. This check is required by 14 CFR part 91, section 91.171 before instrument flight operations.
DISTANCE MEASURING EQUIP-MENT (DME). The operation of DME consists of paired pulses at a specific spacing, sent out from the aircraft (this is what is called interrogation), and are received by the ground station, which then responds with paired pulses at the specific spacing sent by the aircraft, but at a different frequency. The aircraft unit measures the time it takes to transmit and then receive the signal, which then is translated into distance. DME operates on frequencies from 962 MHz to 1213 MHz.
Because of the curvature of earth, this line-ofsight signal is reliable up to 199 nautical mile (NM) at the high end of the controlled airspace with an accuracy of 1/2 mile or 3 percent of the distance. DME inspection/maintenance on the aircraft is most commonly limited to a visual check of the installation, and if there have been previously reported problems, the antenna must be inspected for proper bonding and the absence of corrosion, both on the mounting surface, as well as the coax connector.
Accuracy can be determined by evaluating performance during flight operations, as well as with ground test equipment. If a discrepancy is reported and corrected, it is good practice to make the accuracy determination before instrument flight. Tune the DME to a local station, or use the proper ground test equipment to check audio identification, and DME hold function verify correct display operation.
AUTOMATIC DIRECTION FINDER (ADF). The ADF receivers are primarily designed to receive nondirectional beacons (NDB) in the 19 to 535 kHz amplitude modulation (AM) broadcast low band. The receivers will also operate in the commercial AM band. The ADF display pointer will indicate the relative bearing to a selected AM band transmitter that is in range.
An ADF system must be checked by tuning to an adequate NDB or commercial AM station.
Verify