AN EMBRAER 145 AFTER ROTATION WITH THE FO FLYING HAS THE FO'S SEAT SLIDE FULL AFT AND TO THE R.

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THIS IS FOR INFORMATIONAL PURPOSE TO NASA; I FEEL THE SEVERITY OF THIS ISSUE AS WELL AS REOCCURRENCE WARRANTS DOCUMENTATION. THROUGH THE LAST 6 MONTHS I HAVE HAD A LARGE NUMBER OF FO SEATS COME LOOSE DURING THE TKOF ROLL; USUALLY RIGHT AFTER ROTATION. I HAVE DOCUMENTED THIS IN THE MEL AND MAINT HAS COME OUT; CLEANED THE TRACK THEN LUBRICATED IT TO ALLOW THE TRACK AND PINS TO LOCK IN POS EASIER. 70 PERCENT OF THE TIME THIS WORKS ALLOWING THE PINS TO SEAT SMOOTHER. IT APPEARS THAT THE REAR PINS; EVEN WHEN THEY ARE RECHECKED AND CONFIRMED LOCKED PRIOR TO TKOF ARE NOT FULLY ENGAGING; ALLOWING NO WARNING TO THE PLT WHEN HIS SEAT COMES LOOSE AND SLIDES TO THE FULL AFT POS AT A CRITICAL PHASE OF FLT. I AM EXTRA CAREFUL OF THIS AND I STILL HAVE IT OCCUR. THIS IS AN ISSUE THAT NEEDS TO BE ADDRESSED IN AN EXPEDITIOUS MANNER AS IT SEEMS TO BE HAPPENING WITH BOTH OLD AND NEW TRACKS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THIS LOCKING PROB IS NOT LIMITED TO ONLY THE FO'S SEATS; BUT INCLUDES CAPT SEATS AS WELL. THE RPTR SAID THIS IS A CHRONIC PROB THAT HAS REACHED A POINT WHERE CREWS NOW EXPECT A SEAT LOCKING FAILURE. THE RPTR STATED THE LOCKING LEVER IS PUSHED DOWN TO WHAT APPEARS TO BE A POSITIVE LOCK POSITION AND THE SEAT WILL STILL SLIDE. THE RPTR SAID AT TIMES WHEN THE SEAT IS MOVING THE LOCK LEVER IS PUSHED DOWN WITH NO EFFECT. THE RPTR STATED THE SEAT ENDS UP FULL AFT AND TO THE RIGHT IN THE SEAT ACCESS POS. THE RPTR SAID MODIFIED SEAT RAILS HAVE BEEN INSTALLED; BUT HAS NOT CORRECTED THE SIT.