 +_____________________________________________________________________
  AUTHOR:                                          SMS: B27038      
          C. Kim         BFS PROGRAM NOTE          DR:  108812      
 ____________________                             __________________
  ORG/PHONE:          OPS NOTE (X)  USER NOTE ( )  DATE: 8/20/93    
  RI(D)/310-922-0544       RELEASE NOTE ( )                         
 ___________________________________________________________________
  OI/FLIGHT EFFECTIVITY:          USER AFFECTED:                     
  OI-21 & SUBS                    CREW ( )  GROUND (X)  DUMP ONLY ( )
 ____________________________________________________________________
            MAJOR SOFTWARE AREA:             OPS MODES AFFECTED:     
 BSL( ) BSS( ) GNC(X) SEQ( ) SM/SP( ) IPL( )       3 & 6             
 _____________________________________________________________________
  SOFTWARE SUB-AREA: NAV                                              
 _____________________________________________________________________
  PRINCIPAL FUNCTIONS: MG038104/3.2.2.3.9                             
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  TITLE:                                                              
         BFS Exponent Overflow GPC Errors after MM304                 
 _____________________________________________________________________
  DESCRIPTION:                                                        
                                                                      
  The problem occurs when the Shuttle and the selected HAC center     
  in the earth-fixed coordinate system happen to form an angle of     
  exactly 90 degrees at the precise moment when transition is made    
  to MM304 or MM602.  It is considered to be a rare occurrence.       
                                                                      
  Once the problem occurs, the crew will not be able to detect it     
  since the HSI (Horizontal Situation Indicator) primary and          
  secondary bearing indicators will remain at their null positions    
  as before.  The ground will see it in the downlist as GPC error     
  messages (BOS error code 9A).  However, within a few seconds,       
  the problem will self-correct and disappear since the Shuttle       
  position will change so that the above condition will no longer     
  exist.                                                              
                                                                      
 _____________________________________________________________________
  USER RESPONSE:                                                      
                                                                      
  The problem will not affect the flight software performance and     
  will correct itself within a few seconds.                           
                                                                      
  Therefore the problem may safely be ignored when it occurs.         
                                                                      
                                                                      
                                                                      
 _____________________________________________________________________
 CONCURRENCE:                           APPROVAL:                    
 RI: <s> J. Agres          DATE 09/17/93                             
     --------------------      ---------                             
 FDSD:   W. R. PRUETT      DATE 10/20/93                             
      -------------------      --------- DARRELL E. STAMPER 10/28/93 
 PF MGR:   M. N. MONTEZ    DATE 10/26/93------------------- -------- 
        -----------------      --------- CHAIRMAN, SASCB      DATE   
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