php, 111 bytes

Result

AC

Duration

800ms

Code [DL]

<?php
$b=0;$d=1;while($c=fread(STDIN,1)){if($c=='T')$d=0;$b=$c=='K'||$b&&$d;echo(!$d||$b?'A':$c);$d=($d+1)%51;}

stdin

                       T                          
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
          K                                       

stdout

                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
                       A                          
          AAAAAAAAAAAAAA                          

stderr

strace