 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] DR:              ]
 ] W. J. BRYAN        ]    PASS PROGRAM NOTE        ]     46524        ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE: 11/2/87    ]
 ] IBM/282-7767       ]      RELEASE NOTE( )        ] REV A: 06/14/89  ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ] OI02 AND SUBS                 ]  CREW (X)  GROUND ( )  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]        MAJOR SOFTWARE AREA:       ] OPS MODES AFFECTED:             ]
 ]SSW ( )  GNC (X)  VU ( )  SM/PL ( )] G3                              ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA:  GUID                                            ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: 4.9                                            ]
 ]_____________________________________________________________________]
 ] TITLE: MEP TRAP IN OTT GUIDANCE                                     ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:  MM304                                                 ]
 ]  THERE ARE CASES OF IMPROPER OTT GUIDANCE IF MEP IS SELECTED AFTER  ]
 ]  INTERCEPT OF THE NEP SPIRAL.  THESE CASES ARE LIMITED TO EXTREMELY ]
 ]  LOW ENERGY OVERHEADS.  THE LIKELY CASE (1) IS:                     ]
 ]  CASE 1:                                                            ]
 ]  O  THE VEHICLE IS WELL BELOW THE ALTITUDE REFERENCE AT NEP INTER-  ]
 ]     CEPT.  THE HAC SHRINKS TO MINIMUM RADIUS AND THE VEHICLE HEADS  ]
 ]     TO THE NEW HAC.                                                 ]
 ]  O  CREW SELECTS MEP DUE TO LOW ENERGY AND A NEW RANGE IS CALCULATED]
 ]     BY NAV.  THAT RANGE IS BELOW 30,225 FEET AND GUIDANCE MODES TO  ]
 ]     TAEM PRE-FINAL.                                                 ]
 ]  O  PRE-FINAL BANK ANGLE ALGORITHM ASSUMES HEADING IS WITHIN 90 DE- ]
 ]     GREES OF RUNWAY.  SINCE THIS IS NOT TRUE,  GUIDANCE COMMANDS A  ]
 ]     BANK IN THE WRONG DIRECTION.                                    ]
 ]  O  ONCE THE VEHICLE TURNS TOWARD THE CENTERLINE, GUIDANCE CHECKS   ]
 ]     FOR A MAXIMUM RATE OF CLOSURE.  WHEN THE RATE LIMIT IS REACHED, ]
 ]     GUIDANCE COMMANDS WINGS LEVEL EVEN THOUGH THE VEHICLE IS NOT A- ]
 ]     LIGNED WITH THE RUNWAY CENTERLINE AND MAY NOT REACH THE EXTENDED]
 ]     RUNWAY CENTERLINE PRIOR TO CROSSING THE RUNWAY THRESHOLD.       ]
 ]  CASE 2:                                                            ]
 ]     IF, AS IN CASE 1, MEP IS RESELECTED IN RESPONSE TO HAC SHRINK,  ]
 ]     THE RANGE TO GO IS GREATER THAN 30,225 FEET, AND THE VEHICLE    ]
 ]     GROUNDTRACK IS INSIDE THE MEP SPIRAL, GUIDANCE PROJECTS THE VE- ]
 ]     HICLE CURRENT POSITION TO DEFINE A NEW MEP SPIRAL ACQUISITION   ]
 ]     POINT.  IF THAT PROJECTION CAUSES THE HAC TURN ANGLE TO BE > 180]
 ]     DEGREES TO ALIGN WITH THE RUNWAY CENTERLINE, THEN WINGS LEVEL IS]
 ]     COMMANDED UNTIL Y AND Y ERRORS REACH A LIMIT, THEN THE TURN IS  ]
 ]     RESUMED.  THIS MANEUVER REQUIRES MORE ENERGY THAN IS AVAILABLE. ]
 ]     IF A MANUAL TURN IS FLOWN TO INTERCEPT THE MEP SPIRAL, GUIDANCE ]
 ]     WILL NOT RECOGNIZE THIS INTERCEPT AS THE NEW ACQUISITION POINT  ]
 ]     BUT WOULD TRY TO FLY TOWARD A DIFFERENT ACQUISITION POINT.  THIS]
 ]     MANEUVER ALSO REQUIRES MORE ENERGY THAN IS AVAILABLE.           ]
 ]                                                                     ]
 ]  POSSIBLE I-LOAD CHANGES TO CORRECT THIS HAVE BEEN SUGGESTED.       ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 @



 +_____________________________________________________________________
 ]                       SUPPLEMENTAL SHEET                            ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ] AUTHOR:            ]                             ] DR:              ]
 ] W. J. BRYAN        ]    PASS PROGRAM NOTE        ]     46524        ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE: 11/2/87    ]
 ] IBM/282-7767       ]      RELEASE NOTE ( )       ] REV A: 06/14/89  ]
 ]____________________]_____________________________]__________________]
 ] TITLE:  MEP TRAP IN OTT GUIDANCE                                    ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]USER RESPONSE:                                                       ]
 ]                                                                     ]
 ] NO RESTRICTIONS ON MEP SELECTION FOR STRAIGHT-IN APPROACHES.        ]
 ] FOR OVERHEAD APPROACHES THE FOLLOWING APPLY:                        ]
 ]                                                                     ]
 ]    A.  TRY TO SELECT MEP EARLY IN TAEM.  AVOID MAKING A MEP SELEC-  ]
 ]        TION WITH LESS THAN 20 SECONDS TO SPIRAL INTERCEPT.          ]
 ]    B.  AFTER INTERCEPTING THE NEP SPIRAL, DO NOT DOWNMODE TO MEP AS ]
 ]        A RESPONSE TO HAC SHRINK UNTIL YOU ARE AT OR INSIDE THE 180  ]
 ]        DEGREE TURN-TO-GO POINT.                                     ]
 ]    C.  IF GUIDANCE APPEARS LOST FOLLOWING A MEP SELECTION, TOGGLING ]
 ]        FROM OVERHEAD TO STRAIGHT-IN WILL REGAIN VALID GUIDANCE.     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]IBM: WYATT COOPER         DATE 07/13/89]                             ]
 ]    --------------------      ---------]                             ]
 ]SSD: SAM ANKNEY           DATE 07/14/89]                             ]
 ]    --------------------      ---------] M.C. GREMILLION    08/20/89 ]
 ]PF MGR: LARRY MC WHORTER  DATE 07/28/89]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]_______________________________________]_____________________________]
 @
