 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] DR:              ]
 ] L. GILCHRIST       ]    PASS PROGRAM NOTE        ]    37577         ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE: SEPT. 1987 ]
 ] VER/282-7067       ]      RELEASE NOTE( )        ]                  ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ] REL 19 AND SUBS               ]  CREW (X)  GROUND ( )  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]        MAJOR SOFTWARE AREA:       ] OPS MODES AFFECTED:             ]
 ]SSW ( )  GNC (X)  VU ( )  SM/PL ( )] G1, G3                          ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA: SPEC, DISP                                       ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: 6.21                                           ]
 ]_____________________________________________________________________]
 ] TITLE:                                                              ]
 ] INVALID TACAN BEARING DATA DISPLAYED ON HSD                         ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:                                                        ]
 ] IT IS POSSIBLE FOR THE HORIZONTAL SITUATION SPEC TO DISPLAY TACAN   ]
 ] BEARING DATA VALUES MARKED AS "INVALID" BY THE TACAN SOP.  THIS     ]
 ] CAN OCCUR IN THE CASE WHERE THE TACAN IS ALTERNATELY ACHIEVING AND  ]
 ] LOSING COMM-LOCK APPROXIMATELY ONCE PER SECOND (AS MIGHT OCCUR      ]
 ] BETWEEN ENTRY INTERFACE AND BLACKOUT WHEN TACAN'S ARE IN A MARGINAL ]
 ] RECEPTION REGIME). THIS SITUATION IS MADE POSSIBLE DUE TO A         ]
 ] REQUIREMENTS CONFLICT IN THAT THE TACAN DISPLAY COMPUTATIONS ARE    ]
 ] ONLY REQUIRED TO EXECUTE ON EVERY OTHER CYCLE (.52HZ) THAT TACAN RM ]
 ] EXECUTES (1.04HZ). TACAN DISPLAY VALUES ARE CYCLICALLY COMPUTED FROM]
 ] TACAN SOP INPUTS AT .52HZ REGARDLESS OF VALIDITY STATUS, PER        ]
 ] REQUIREMENTS. THUS, INVALID VALUES RECEIVED ON THE PREVIOUS SOP     ]
 ] CYCLE, WHICH WERE AT THAT TIME PROCESSED FOR DISPLAY, WILL BE       ]
 ] DISPLAYED (CARRIED OVER FROM PREVIOUS CYCLE) ON THE NEXT SOP CYCLE  ]
 ] IF THE VALIDITY STATUS IS "GOOD" ON THAT SOP CYCLE. THIS SITUATION  ]
 ] OCCURS ON A PER TACAN BASIS DEPENDING ON EACH TACAN'S COMM-LOCK     ]
 ] STATUS. IT MUST BE NOTED THAT THIS IS A DISPLAY ISSUE ONLY. ALSO,   ]
 ] FOR FLIGHT REGIMES WHEN TACAN DATA ARE REQUIRED TO BE USED BY       ]
 ] NAVIGATION, THE PROBABILITY OF 1HZ OSCILLATING COMM-LOCK STATUS IS  ]
 ] EXTREMELY LOW.                                                      ]
 ]_____________________________________________________________________]
 ] USER RESPONSE:                                                      ]
 ] BE AWARE OF THE POTENTIAL TO DISPLAY INVALID BEARING DATA. THIS     ]
 ] WILL USUALLY BE ACCOMPANIED BY "M'S" INTERMITTENTLY APPEARING IN    ]
 ] PLACE OF THE DATA SINCE THE EXACT PHASING OF OSCILLATING COMM-LOCK  ]
 ] WILL VARY. CONSIDER THIS SIGNATURE TO BE INDICATIVE OF INTERMITTENT ]
 ] TACAN COMM-LOCK, A CONDITION FOR WHICH TACAN DATA SHOULD NOT BE     ]
 ] INCORPORATED INTO THE NAV STATE PROCESSING.                         ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]IBM: WYATT COOPER         DATE 9/20/88 ]                             ]
 ]    --------------------      ---------]                             ]
 ]SSD: SAM ANKNEY           DATE 9/20/88 ]                             ]
 ]    --------------------      ---------] JACK G BOYKIN       9/22/88 ]
 ]PF MGR: GEORGE BULL JR    DATE 9/14/88 ]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]_______________________________________]_____________________________]
 @
 DR37584
