 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] DR:              ]
 ] J. MAGLEY          ]    PASS PROGRAM NOTE        ]        45603     ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE: SEPT. 1987 ]
 ] SSOAS/282-7596     ]      RELEASE NOTE( )        ] REV A: 06/13/96  ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ]  OI-25 AND SUBS               ]  CREW (X)  GROUND (X)  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]        MAJOR SOFTWARE AREA:       ] OPS MODES AFFECTED:             ]
 ]SSW ( )  GNC (X)  VU ( )  SM/PL ( )] G3                              ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA: IMU, TRANSITIONS, NAV                            ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: 4.72, 4.127                                    ]
 ]_____________________________________________________________________]
 ] TITLE:                                                              ]
 ] TWO IMU FAILURES CAN CAUSE NAV STATE DISCONTINUITY AT OPS TRANSITION]
 ]_____________________________________________________________________]
 ] DESCRIPTION:                                                        ]
 ]                                                                     ]
 ] A NAV STATE JUMP MAY BE OBSERVED UPON TRANSITION INTO OPS 3 IF ONE  ]
 ] IMU HAD PREVIOUSLY BEEN FAILED AND A SECOND IMU (VEL PARAMETER      ]
 ] ONLY) FAILS WITHIN 32 SECS BEFORE OPS TRANSITION. DEPENDING ON THE  ]
 ] FAILURE MODE, IT IS POSSIBLE THAT THE VEL IMU SF WILL NOT BE ABLE   ]
 ] TO ISOLATE THIS FAILURE IN OPS 3 AND THUS CAUSE NAV TO BELIEVE THAT ]
 ] BOTH IMU'S ARE AVAILABLE FOR USE. FURTHERMORE, IT WILL BE           ]
 ] APPROXIMATELY 32 SECS BEFORE VEL IMU FDIR COULD ISOLATE THE BAD IMU ]
 ] AND DOWNMODE THE VEL IMU SF (IF IT CAN ISOLATE THE BAD IMU) OR      ]
 ] APPROXIMATELY 64 SECS BEFORE A DILEMMA WILL BE ANNUNCIATED TO THE   ]
 ] CREW (IF VEL IMU FDIR CAN'T ISOLATE THE BAD IMU ). IF VEL IMU FDIR  ]
 ] CAN'T ISOLATE THE BAD IMU, THE CREW WILL HAVE TO DO IT AND DESELECT ]
 ] THAT IMU. WHEN THE BAD IMU IS FAILED (OR DESELECTED), THE NAV STATE ]
 ] WILL JUMP AGAIN (BACK TO A GOOD VALUE).                             ]
 ]_____________________________________________________________________]
 ] USER RESPONSE:                                                      ]
 ]                                                                     ]
 ] UNLESS AN IMU DILEMMA IS ANNUNCIATED, THERE IS NO CREW RESPONSE     ]
 ] OTHER THAN WAITING FOR IMU RM TO SOLVE THE PROBLEM. IF AN IMU       ]
 ] DILEMMA IS ANNUNCIATED, THE CREW MUST DESELECT THE BAD IMU (USING   ]
 ] THE IMU ALIGN DISPLAY OR THE OVERRIDE DISPLAY).                     ]
 ]                                                                     ]
 ] NAV STATE DISCONTINUITIES OBSERVED ON THE GROUND VIA DOWNLIST IN    ]
 ] THE PROXIMITY OF RECENT OPS TRANSITIONS MUST CONSIDER THIS          ]
 ] POTENTIAL SCENARIO AS A POSSIBLE SOURCE OF THE OBSERVED ANOMALY.    ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]SSOAS:  JEAN L. ZOPHY     DATE 07/09/96]                             ]
 ]      ------------------      ---------]                             ]
 ]ASD:   ERIC C. BINGHAM    DATE 07/09/96]                             ]
 ]    --------------------      ---------] DARRELL E. STAMPER 07/15/96 ]
 ]PF MGR:  M. N. MONTEZ     DATE 07/12/96]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]_______________________________________]_____________________________]
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