TABLE 11-29. ELECTRONIC/ELECTRICAL SYMBOLS (CONTINUED) Symbol Meaning Governor Speed Regulator
AC D DP MC
I P DB EP NB ) SO SA SW ) SR L ML FR · Relay Inertia Switch Mercur Switch Terminals Par 11-272 Page 11-129
TABLE 11-29. 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 11-130
TABLE 11-29. ELECTRONIC/ELECTRICAL SYMBOLS (CONTINUED) Symbol Meaning Fuse Lightning Arrester Arrester Gap Circuit Breaker
- CC Protective Relay F S GP T =00 Audible-Signaling Device Microphone Par 11-272 Page 11-131
TABLE 11-29. ELECTRONIC/ELECTRICAL SYMBOLS (CONTINUED) Symbol Meaning Handset Operator's Set Lamp ₩ Visual-Signaling Device Mechanical Connection Mechanical Interlock Mechanical Motion ~ Clutch Brake Par 11-272 Page 11-132
TABLE 11-29. ELECTRONIC/ELECTRICAL SYMBOLS (CONTINUED) Symbol Meaning Manual Control Gyro Gyposcope Gyrocompass Position Indicator Fire Extinguisher Actuator Head Position Transmitter Radio Station a 5· Space Station Par 11-272 Page 11-133
TABLE 11-29. ELECTRONIC/ELECTRICAL SYMBOLS (CONTINUED) Integrated Circuit Amplifiers
GENERAL SYMBOLS MAGNETIC AMPLIFIER
INVERTOR OR
NOT GATE AND GATE WITH THREE INPUTS NAND (NOT AND) GATE Logic Gates
OR GATE NOR (NOT OR) GATE
EXCLUSIVE OR GATE Diode
EMITTER BASE COLLECTOR Transistor Symbols
EMITTER BASE COLLECTOR E - C N
11-273.-11-283. [RESERVED.] Par 11-272 Page 11-134
Par 12-1 Page 12-1 CHAPTER 12. AIRCRAFT AVIONICS SYSTEMS SECTION 1. AVIONICS EQUIPMENT MAINTENANCE
12-1. GENERAL. There are several methods of ground checking avionics systems.
a. Visual Check. Check for physical condition and safety of equipment and components.
b. Operation Check. This check is performed primarily by the pilot, but may also be performed by the mechanics after annual and 100-hour inspections. The Aircraft Flight Manual (AFM), the Airman’s Information Manual (AIM), and the manufacturer’s information are used as a reference when performing the check.
c. Functional Test. This is performed by qualified mechanics and repair stations 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.
d. Bench Test. When using this method the unit or instrument is removed from the aircraft and inspected, repaired, and calibrated as required.
e. Electromagnetic Interference (EMI). For EMI tests, refer to chapter 11, paragraph 11-107 of this AC.
12-2. HANDLING OF COMPONENTS. Any unit containing electronic components such as transistors, diodes, integrated circuits, programmable read-only memory (PROM), Read-Only Memory (ROM), and memory devices should be protected from excessive shocks. Excessive shock can cause internal failures 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 12-2 SECTION 2. GROUND OPERATIONAL CHECKS FOR AVIONICS EQUIPMENT (ELECTRICAL)
12-8. 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.
12-9. INSPECTION OF AVIONICS SYSTEMS.
a. The inspection shall include the following:
(1) Inspect the condition and security of equipment including the proper security of wiring bundles.
(2) Check for indications of overheating of the equipment and associated wiring.
(3) 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.
(4) Check to assure that the radios and instruments are secured to the instrument panel.
(5) 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.
(6) Check the microphone headset plugs and connectors and all switches and controls for condition and operation. Check all avionics instruments for placards. Check lighting, annunciator lights, and cockpit interphone for proper operation.
(7) The circuit breaker panel must be inspected for the presence of placarding for each circuit breaker installed.
(8) 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.
Par 12-9 Page 12-3
b. Inspect antennas for:
(1) Broken or missing antenna insulators,
(2) Lead through insulators,
(3) Springs,
(4) Safety wires,
(5) Cracked antenna housing,
(6) Missing or poor sealant at base of antenna,
(7) Correct installation,
(8) Signs of corrosion,
(9) The condition of paint/bonding and grounding, and
(10) Check the bonding of each antenna from mounting base to the aircraft skin.
Tolerance: .1 ohm, maximum.
(a) Test equipment:
1. 1502B Metallic Time Domain Reflectometer or equivalent.
2. Thruline Wattmeter.
(b) 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.
(c) Use Thruline wattmeter as needed for addition evaluation. Refer to manufacturer’s maintenance procedures. Check for the following:
1. Resistance.
2. Shorts.
3. Opens.
c. Inspect the static dischargers/wicks for:
(1) Physical security of mounting attachments, wear or abrasion of wicks, missing wicks, etc.;
(2) Assurance that 1 inch of the inner braid of flexible vinyl cover wicks extends beyond the vinyl covering;
Par 12-9 Page 12-4
(3) Assurance that all dischargers are present and securely mounted to their base;
(4) Assurance that all bases are securely bonded to skin of aircraft in order to prevent the existence in voltage level differences between two surfaces;
(5) Signs of excessive erosion or deterioration of discharger tip;
(6) Lightning damage as evidenced by pitting of the metal base; and
(7) Megohm value of static wick itself as per manufacturer’s instructions. It should not be open.
d. 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, §§ 91.411 and 91.413.
e. Inspection of the emergency locator transmitter (ELT) operation, condition, and date of the battery.
f. 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.
12-10. 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 headphones, speaker(s), and hand microphone. If a receiver or transmitter is found to be defective, it should be removed from the aircraft and repaired.
12-11. VHF OMNI-DIRECTIONAL RANGE (VOR). A VOR operates within the 108.0 to
111.85 MHz, and 112.0 to 117.95 MHz frequency bands. 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 using a slaved compass system, which uses an additional indicator that points continually to the selected omni station regardless of OBS. In order to determine the accuracy specified in a functional check, a ground test set must be used in accordance with 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) interface, and applicable navigation (NAV) switching functions. The operational check is also published in the AIM, section 1-1-4. This check is required by § 91.171 before instrument flight operations.
12-12. DISTANCE MEASURING EQUIPMENT (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
Par 12-12 Page 12-5 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 1,213 MHz. Because of the curvature of earth, this line-of-sight 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.
12-13. 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 proper bearing to station, audio identification and tone/beat frequency oscillator (BFO), correct operation in closed circuit (LOOP) and sense modes. Note the orientation of the selected station to the aircraft using an appropriate chart. Observe the ADF relative bearing reading, and compare to the chart. Slew the needle and observe how fast (or slowly) it returns to the reading. ADF performance may be degraded by lightning activity, airframe charging, ignition noise and atmospheric phenomena.
12-14. INSTRUMENT LANDING SYSTEMS (ILS). The ILS consist of several components, such as the localizer (LOC), glideslope (GS), marker beacon, radio altimeter, and DME. LOC and GS receivers and marker beacons will be discussed in this section.
a. LOC receiver operates on one of 40 ILS channels within the frequency range of
108.10 to 111.95 MHz (odd tens). These signals provide course guidance to the pilot to the runway center line through the lateral displacement of the VOR/LOC deviation indicator. The ground transmitter is sighted at the far end of the runway and provides a valid signal from a distance of 18 NM from the transmitter. The indication gives a full fly left/right deviation of 700 ft at the runway threshold. Identification of the transmitter is in International Morse Code and consists of a three letter identifier preceded by the Morse Code letter I (two dots). The LOC function is usually integral with the VOR system, and when maintenance is performed on the VOR unit, the LOC is also included. The accuracy of the system can be effectively evaluated through normal flight operations if evaluated during visual meteorological conditions (VMC).
Any determination of airworthiness after reinstallation before instrument flight must be accomplished with ground test equipment.
b. The GS receiver operates on one of 40 channels within the frequency range
329.15 MHz to 335.00 MHz. The GS transmitter is located between 750 ft and 1,250 ft from the approach end of the runway and offset 250 to 650 ft. In the absence of questionable performance, periodic functional flight checks of the GS system would be an acceptable way to ensure
Par 12-14 Page 12-6 continued system performance. The functional flight test must be conducted under visual flight rules (VFR) conditions. A failed or misleading system must be serviced by an appropriately rated repair station. Ground test equipment can be used to verify GS operation.
c. LOC/GS may have self-test function, otherwise the proper ground test equipment must be used. Refer to manufacturers’ or aircraft instruction manual.
12-15. MARKER BEACON. Marker beacon receivers operate at 75 MHz and sense the audio signature of each of the three types of beacons. The marker beacon receiver is not tunable. The blue outer marker light illuminates when the receiver acquires a 75 MHz signal modulated with 400 Hz, an amber middle marker light for a 75 MHz signal modulated with 1,300 Hz and, a white inner marker light for a 75 MHz signal modulated with 3,000 Hz. The marker beacon system must be operationally evaluated in VFR when an ILS runway is available. The receiver sensitivity switch must be placed in LOW SENSE (the normal setting). Marker audio must be adequate. Ground test equipment must be used to verify marker beacon operation. Marker beacon with self-test feature, verify lamps, audio and lamp dimming.
12-16. LONG RANGE NAVIGATION (LORAN). The LORAN has been an effective alternative to Rho/Theta R-Nav systems. Hyperbolic systems require waypoint designation in terms of latitude and longitude, unlike original R-Nav (distance navigation) systems, which define waypoints in terms of distance (Rho) and angle (Theta) from established VOR or Tactical Air Navigation System (TACAN) facilities. Accuracy is better than the VOR/TACAN but LORAN is more prone to problems with precipitation static. Proper bonding of aircraft structure and the use of high-quality static wicks will not only produce improved LORAN system performance, but can also benefit the very high frequency (VHF) navigation and communications systems. This system has an automatic test equipment (ATE). Normally, self-test check units, verification of position, and loading of flight plan will verify operation verification of proper flight manual supplements and operating handbooks on board, and proper software status can also be verified.
NOTE: Aircraft must be outside of hangar for LORAN to operate.
12-17. GLOBAL POSITIONING SYSTEM (GPS). The GPS is now one of the most common generation navigation systems. This space-based navigation system is based on a 24-satellite system and is highly accurate for establishing position. The actual accuracy users attain depends on factors outside the user’s control, including atmospheric effects, sky blockage, and receiver quality. Real-world data shows that high-quality GPS receivers provide better than 3.5 meter horizontal accuracy. The system is largely unaffected by weather and provides a worldwide common grid reference system. Database updating and antenna maintenance are of primary concern to the GPS user.
NOTE: Aircraft must be outside of hangar for ground test of GPS.
12-18. AUTOPILOT SYSTEMS. Automatic flight control systems (AFCS) are the most efficient managers of aircraft performance and control. There are three kinds of autopilot; two axes, three axes, and three axes with coupled approach capability. Attention must be given to the disconnect switch operation, aural and visual alerts of automatic and intentional autopilot