Aircraft Digital Computer Systems PDF

Aircraft Digital Computer Systems  CMC SYSTEM ARCHITECTURE Introduction When the mechanic receives the pilot’s complaint, it should be possible to start trouble shooting to locate the source of the failure in an economical way. On old generation aircraft, you need to know many different methods o...

Aircraft Digital Computer Systems  CMC SYSTEM ARCHITECTURE Introduction When the mechanic receives the pilot’s complaint, it should be possible to start trouble shooting to locate the source of the failure in an economical way. On old generation aircraft, you need to know many different methods of trouble shooting.  CMC SYSTEM ARCHITECTURE Introduction For instance each system test is performed with an individual switch either located on a cockpit panel or on the front side of different computers and in different locations with specific methods of test result presentation.  CMC SYSTEM ARCHITECTURE Introduction Modern aircraft such as the A340, A320 and 747--400, have a central Maintenance computer system or CMCS. The CMCS provides a central location in the cockpit for trouble shooting with standardized methods of testing and fault reporting. CMC SYSTEM ARCHITECTURE  CMC SYSTEM ARCHITECTURE The central maintenance computer system consists of: 1. One or two central maintenance computers or CMC located in the avionic compartment 2. Two or three Multi-purpose Control and Display Units or MCDU in the cockpit as the main interface between the operator and the system  CMC SYSTEM ARCHITECTURE Central Maintenance Computers or CMC MCDU CMC SYSTEM ARCHITECTURE MCDU  CMC SYSTEM ARCHITECTURE The central maintenance computer system consist of: 3. A printer in the cockpit for hardcopies of the information. 4. A connection to the datalink system called ACARS, for transmission of the information to the homebase. CMC SYSTEM ARCHITECTURE CMC SYSTEM ARCHITECTURE CMC SYSTEM ARCHITECTURE CMC SYSTEM ARCHITECTURE CMC SYSTEM ARCHITECTURE ACARS  CMC SYSTEM ARCHITECTURE The central maintenance computer system consist of: 5. A digital computer in each aircraft system which is connected to the CMC in order to provide the trouble shooting information.  CMC SYSTEM ARCHITECTURE The aircraft systems that are connected to the CMC are those made up of many components. These systems need a computer to manage their normal operation and it is often difficult to locate a failure source in them.  CMC SYSTEM ARCHITECTURE Typical examples of such systems are the engine control system, all types of avionic equipment such as navigation, communication, instruments and auto flight systems, the fuel system, the landing gear and brake system and the flight control system. CMC SYSTEM ARCHITECTURE CMC SYSTEM ARCHITECTURE CMC SYSTEM ARCHITECTURE The total number of complex systems that are connected to the CMC varies from aircraft to aircraft but is between 50 and 100.  CMC SYSTEM ARCHITECTURE Simple aircraft systems, such as the water system, which have a small number of components, are not connected to the CMC. Trouble shooting for these systems must be performed in the conventional way.  CMC SYSTEM ARCHITECTURE Note that the CMCS and its components can have different names in different aircraft. For instance in the A320 the CMC is called the centralized fault display interface unit (CFDIU) and the CMCS is called the centralized fault display system (CFDS). However, the general function is identical. CMC SYSTEM ARCHITECTURE CMC Schematic  CMC SYSTEM ARCHITECTURE CMCS Functions The CMCS has two modes of operation. The modes are called reporting mode interactive mode.  CMC SYSTEM ARCHITECTURE CMCS Functions The first mode is called the reporting mode. In this mode, the CMC scans all of the aircraft systems that are connected to it. As it does this, the CMC memorizes the transmitted fault information. CMC SYSTEM ARCHITECTURE CMCS Functions This memorized fault information can be read at anytime by use of the MCDU or a printout from the printer. It can also be sent to the homebase via the datalink system. CMC SYSTEM ARCHITECTURE Reporting Mode  CMC SYSTEM ARCHITECTURE CMCS Functions The second mode is the interactive mode. This mode can be selected only on the ground and is mainly used for system tests. To start the interactive mode, select one aircraft system from the MCDU followed by a test start signal to the selected system that now performs the test. CMC SYSTEM ARCHITECTURE CMCS Functions Finally, the aircraft system sends back the test results. These results can then be read on the MCDU or on the printout from the printer or it can be sent via the datalink to the homebase. CMC SYSTEM ARCHITECTURE Interactive Mode  CMC SYSTEM ARCHITECTURE CMCS Functions The CMC communicates with the computers of the aircraft systems via a specialized portion of the computers called the BITE. BITE stands for built in test equipment.  CMC SYSTEM ARCHITECTURE CMCS Functions The BITE is located inside each aircraft system computer but is completely independent from its operational part. CMC SYSTEM ARCHITECTURE CMCS Functions The BITE has 2 functions detect failures perform tests on the ground.  CMC SYSTEM ARCHITECTURE CMCS Functions The first of these functions to detect failures occurs during the normal operation of the system. It identifies the most probable cause of the failure and sends this to the CMC.  CMC SYSTEM ARCHITECTURE CMCS Functions The second function of the BITE, to perform system tests, only occurs when the aircraft is on the ground.  CMC SYSTEM ARCHITECTURE CMCS Functions The test happens automatically when electrical power is switched on -- this is the power up test. The same test and sometimes additional tests can be started manually from the CMC. The test result is then sent to the CMC. CMC SYSTEM ARCHITECTURE BITE  CMCS REDUNDANCY In the reporting mode, information from the various BITES is stored in the memory of the CMC. To be able to read this information after the flight the CMC must be operational.  CMCS REDUNDANCY However, if the CMC fails during flight, this would have a major influence on the maintenance activities. It would not be possible to read data or perform tests from the MCDU. Therefore the CMCS must have a  CMCS REDUNDANCY This is completely fulfilled with a second standby CMC. This identical CMC receives the same input data and the output becomes active automatically when the normal CMC fails. CMCS REDUNDANCY  CMCS REDUNDANCY On some aircraft, the standby CMC can be activated by pressing a control pushbutton even if the normal CMC is working. CMCS REDUNDANCY CMCS Redundancy  CMCS REDUNDANCY Redundancy is also possible via a backup channel on the CMC but this is limited to the interactive mode only. CMCS REDUNDANCY CMC Backup Channel  CMCS REDUNDANCY MCDU Basics The MCDU consist of a control area with many push buttons and one control knob a display area which can be either a color or monochrome cathode ray tube or CRT and several annunciator lights to provide information to the operator. CMCS REDUNDANCY  CMCS REDUNDANCY MCDU Basics The MCDU is used mainly during flight to control the flight management system. Many of the control pushbuttons and annunciators are only used for that function and will not be discussed here.  CMCS REDUNDANCY MCDU Basics The only annunciator that is important for CMC use is the FAIL annunciator. It shows you that this MCDU is defective and that you must use another one. The MCDU MENU annunciator is also not used for CMC operation and its function will therefore not  CMCS REDUNDANCY MCDU Basics The brightness control knob switches the MCDU on or off. Normally a flight management system display page appears when the display is first switched on. This knob also allows adjustment of the display brightness.  CMCS REDUNDANCY MCDU Basics Note: that on some types of MCDU it is not possible to switch the display completely OFF but only to decrease it in brightness. CMCS REDUNDANCY  CMCS REDUNDANCY MCDU CMCS Data After pressing the MCDU MENU pushbutton the MCDU MENU shows the systems which are connected to the MCDU. Different systems can be selected and you can read their abbreviations on the display.  CMCS REDUNDANCY MCDU CMCS Data 1.FM as we know already, stands for flight management, which is the system normally selected during flight. 2.ACARS stands for aircraft communication, addressing and reporting system. This is the datalink system that can also be used for the CMCS.  CMCS REDUNDANCY MCDU CMCS Data 3.ACMS stands for aircraft condition monitoring system and provides information about the engine, APU and certain system condition. 4.CMS is the A340 abbreviation for the CMCS and stands for central maintenance  CMCS REDUNDANCY MCDU CMCS Data A symbol, called the prompt, is shown adjacent to a system or function that can be selected. The prompt points to a pushbutton called a line select key.  CMCS REDUNDANCY MCDU CMCS Data The line select key is pressed to select the required function. There are a total of 12 line select keys called 1L to 6L and 1R to 6R. On the lowest display line is the SELECT DESIRED SYSTEM message. This shows that you have the choice to select the  CMCS REDUNDANCY Note: that only the system abbreviations are different on different MCDU’s. CMCS REDUNDANCY  CMCS REDUNDANCY MCDU CMCS Data Pressing line select key 4 Left gives you the CMCS maintenance menu. As you can see, this allows the selection of the different CMC functions. CMCS REDUNDANCY  CMCS REDUNDANCY MCDU Display and Data Entry The display screen consists 14 lines with a maximum of 24 characters in each. The top line is called the title line and shows the title of the selected display. Below the title line are 12 data lines.  CMCS REDUNDANCY MCDU Display and Data Entry The data lines are arranged in 6 pairs with a label line in small fonts at the top and a data line in large fonts below it. Each data line has a right and left line select key.  CMCS REDUNDANCY MCDU Display and Data Entry The bottom line is called the scratchpad or message line. In this line the MCD gives messages to the operator such as select desired system which we have seen already. CMCS REDUNDANCY  CMCS REDUNDANCY MCDU Display and Data Entry The scratchpad is also used to enter alpha numeric data into the data lines. This is always necessary if boxes appear in the data line. To enter data, type the necessary alpha numeric keys.  CMCS REDUNDANCY MCDU Display and Data Entry The typed data appears in the scratchpad you must then press the LS key adjacent to the boxes. The data is then transfered from the scratchpad to the data field.  CMCS REDUNDANCY MCDU Display and Data Entry Sometimes when you press the line select key the data entry is not accepted. This occurs if the data that you have typed is too long to fit into the boxed data field or exceeds an allowed value. In this case press the CLEAR pushbutton on the alpha numeric CMCS REDUNDANCY