EE 2145230 Chapter 12 Design and Maintenance of Aircraft System 12.1 Requirements for Electrical Systems Proper maintenance of aircraft requires that the electrical systems be kept in the best possible condition through inspection, testing and the exercise of approved maintenance procedures. For commercial and other civil aircraft, the requirements for the installation and approval of electric components and materials are established by the Federal Aviation Administration (FAA) and published in Federal Aviation Regulations (FARs). FAR Part 23: Requirements for normal, utility and acrobatic aircraft. FAR Part 25: requirements for transport category aircraft. 1
All systems and equipment installed in transport category aircraft must meet certain basic safety requirements set forth in FAR part 25. In UK: Civil Aviation Authority (CAA) http://www.caa.co.uk/ 2
Individual electric circuits are wired in parallel with respect to each other so that operation of any one circuit will not adversely affect the simultaneous operation of the any other circuit. Schematic diagram is an electrical road map that identifies the various wires and electric components of a particular system. Schematic diagrams usually represent the electrical configurations of one or more systems. Schematic diagrams do not represent the location of electric components within the aircraft or with respect to other components of the system. The manufacturers of corporate and transport category aircraft typically follows the Air Transport Association (ATA) specifications for categorizing data in the maintenance and wiring diagram manuals. See Landing light schematic diagrams of three aviation aircraft producers: Beechcraft, Cessna and Piper in textbook 1. http://www.hawkerbeechcraft.com/ http://www.cessna.com/ Cessna Aircraft Company, Wichita, Kansas 3
http://www.piper.com/ Piper Aircraft Corporation, Lock Haven, Pennsylvania 12.2 Aircraft Lights Lighting is needed for the illumination of instruments, switches and panels. There are various types of lights in aircraft such as position lights, anti collision lights, landing lights, instrument lights, warning lights, and cabin lights. Each aircraft has three position lights (navigation lights): two forward and one at the back. Two forward lights are mounted on the tips of the wings. The right position is green and the left is red. The aft (back) light is white and mounted as far to the rear as possible. An anti collision light is designed to make the presence of an aircraft visible to the pilots and crew members of other aircrafts in the vicinity and in conditions of reduced visibility. The anti collision light is of high intensity and flashes on and off. 4
The rotating beacon comprises a filament lamp, reflector, motor and drive mechanism that gives the effect of a light through a red filter that flashes 40 50 times per second. They are located on tail fins and the upper and lower fuselage (or tail boom on a helicopter). Strobe lights are wing tip and tail fin mounted to supplement navigation lights. The strobe light produces a high intensity white flash of 1 ms duration at approximately 70 flashes per minute through a white or red filter; these provide light that can be seen from several miles. Landing lights for an aircraft are required to provide adequate light to illuminate the runway when the aircraft is making a landing. Instrument lights are installed behind the face of the instrument panel. The lights illuminate the instruments but do not shine directly toward the pilot or copilot. Warning lights are provided to alert the pilot or crew to operating conditions within the aircraft systems. Red lights are used to indicate the danger, amber light is indicate caution and green lights to indicate safe conditions. 5
12.3 Large Aircraft Electrical Systems Built in Test Equipment (BITE) systems are used to monitor and detect faults in a variety of aircraft systems. BITE systems continuously test various systems and store all fault information. 6
Electronic Control Units: Generator Control Unit (GCU), Ground Power Control Unit (GPCU), Flight Management Computer (FMC), Electronic Centralized Aircraft Monitoring (ECAM) Flight Data Recorder (FDR): In aviation, a "black box" (they are actually bright orange, to facilitate their being found after a crash) is an audio recording device in the cockpit of an airplane or helicopter. It records the conversation of the pilots during a flight, so if something goes very wrong, investigators can use the black box recording to determine what happened. Although these devices were originally called black boxes for a different reason, they are also an example of a black box according to the meaning above, in that it is of no concern how the recording is actually made. Digital Flight Data Recorders (DFDR) are generally used in modern aircrafts. Several digital data buses are distributed on an aircraft and integrated as one of the many avionic systems. 12.4 Maintenance and Troubleshooting of Electrical Systems Inspection schedules: 100 hour, annual or the periodic inspection program, and continuous airworthiness inspection programs Multimeter troubleshootings by using 1) Voltmeter to detect open circuits (opens), 2) Ohmmeter to detect short circuits (shorts) and 3) Ammeter to test aircraft charging systems. Multipurpose control display unit (MCDU) is used to access a slightly more advanced BITE system. Control Display Unit (CDU) is used to access and display faults and located in the center console of the flight deck. HelicopteCessna: CJ1 7
Beechcraft: Hawk4000 References: Textbooks # 1 and # 2 and websites EE 2145230 Aircraft Electricity and Electronics Asst. Prof. Thavatchai Tayjasanant, Ph.D. 8