An overall check of a computer can be done by the use of a maintenance program. The maintenance program provides a thorough and rapid method for the detection  of  failures  in  a  specific  portion  of  the computer. This type of overall maintenance check is flexible  and  efficient.  The  programs  may  use  the same type of tape, memory, computing, and external storage   media   as   operational   programs.   The maintenance  program  can  be  altered  when  the computer or auxiliary components are changed. The program can also be constantly improved. Generally, no extra test equipment is required since the computer circuits are used to perform the test. Testing by means of  maintenance  programs  results  in  the  computer circuits being used in a more comprehensive manner than   during   normal   program   execution.   When   a program  has  been  checked  and  accepted  as  a  good maintenance  tool,  it  is  not  subject  to  deterioration.  In contrast, test equipment may be checked and accepted only to become unreliable shortly after being placed in use. Maintenance  programs  are  divided  into  two  main classes: reliability   and   diagnostic.   Maintenance programs  that  are  used  to  detect  the  existence  of errors  are  called  reliability  programs.  Reliability programs  should  be  arranged  to  check  as  many computer  circuits  as  possible. Maintenance programs that are used to locate the circuits  in  which  computer  malfunctions  originate  are called  diagnostic  programs.  An  effective  diagnostic program  should  locate  the  source  of  trouble  as  closely as   possible.   Actually,   in   many   cases,   reliability programs  have  some  diagnostic  features,  just  as diagnostic programs have some reliability features. For   convenience,   a   program   is   called   either   a reliability  or  diagnostic  program,  depending  on  its intended  emphasis.    In general, programs that check rather  than  diagnose  are  shorter  and  simpler. PERIPHERAL  AVIONICS  SYSTEMS Learning   Objective:   Identify   peripheral avionics   systems   and   describe   their interaction with the computer. The  aircraft  computer  is  considered  the  most important  avionics  system  in  achieving  the  mission  of the  aircraft.  However,  the  success  of  the  computer depends upon its external sensors or other avionics systems.  The  quality  of  data  fed  to  the  computer determines the quality of data fed out of the computer. The following avionics systems provide inputs to and receive  outputs  from  the  computer:  navigation,  radar, ordnance/weapons, and data link. These are only a few   of   the   major   aircraft   avionics   systems   that interface with the airborne computer. NAVIGATION Navigation  systems  are  designed  to  tell  pilots where they are, where they have been, and where they are  going.  The  TACAN/DME  system  provides known  station  reference  points,  while  an  inertial navigation  system  provides  continuous  updating  of such  information  as  latitude  and  longitude.  This information  is  fed  to  the  computer  where  it  is compared, updated, and sent out to other systems. SEARCH/TRACK   RADAR A search radar system is designed to give visual indications of what is around the aircraft. Some of the present-day aircraft have a 150-mile or greater range. Depending upon the size and/or speed of the radar indications, a computer can determine whether the target  is  stationary  or  moving,  a  land  mass  or  an aircraft,  friendly  or  unfriendly,  and  many  other  items of  information.  If  a  target  is  determined  to  be unfriendly, a tracking radar can be used to tell the pilot what to do to eliminate the target. ORDNANCE/WEAPONS The  design  characteristics  and  ballistics  of  the many   types   of   ordnance,   weapons,   and   missiles require the use of a computer to store the information. The   airborne   computer   aids   the   pilot   by   telling him/her when to release the weapons. The computer greatly  increases  the  pilot’s  chances  of  destroying designated  targets. DATA LINK Combat  aircraft  have  to  have  the  most  up-to-date information   available   to   successfully   complete combat missions. On an aircraft carrier, the combat information  center,  CIC,  is  normally  in  constant contact with an airborne CIC. The airborne CIC is usually an E-2 or P-3 aircraft. These two CICs will crosstalk by use of the data link system. Basically, data link involves a series of transmitted pulses that represent  information.  The  pulsed  information  is  sent to  the  computers  of  all  combat  aircraft  to  enhance their  chances  of  success. 8-16