Flight crew FMC CDU Controls and indicators Data buses Engine control & monitoring (indicating & alerting) Radio NAV VOR ADF DME ILS RAD. ALT ATC transponder WXR GPWS ADC TMC IRS AFCS FMC Navigation database Operational  program EFIS  symbol generators Control panels AFCS mode IRS mode ILS EFIS ATC VOR/DME RDMI ADF WXR EFIS ADI HSI Maintenance control and display Antennae Control surface servos Database loading Autothrottle servos Sensing probes Discrete inputs from aircraft systems Fuel quantity & fuel flow data Figure 10-126.  A flight management system (FMS) integrates numerous engine, aircraft, and navigational systems to provide overall  management of the flight.  Instrument Housings and Handling 10-78 clocks are often used in multiengine aircraft where complete  loss of electrical power is unlikely.  Many modern aircraft have a digital electronic clock with  LED readout. This device comes with the advantages of low  power consumption and high reliability due to the lack of  moving parts. It is also very accurate. Solid-state electronics  allow for expanded features, such as elapsed time, flight  time that starts automatically upon takeoff, a stop watch, and  memories for all functions. Some even have temperature and  date readouts. Although wired into the aircraft’s electrical  system, electronic digital clocks may include a small  independent battery inside the unit that operates the device  should aircraft electrical power fail.  [Figure 10-132] On aircraft with fully digital computerized instrument  systems utilizing flat panel displays, the computer’s internal  clock, or a GPS clock, can be used with a digital time readout  usually located somewhere on the primary flight display.  Various materials are used to protect the inner workings of  aircraft instruments, as well as to enhance the performance 