AN EMBRAER 145 ON TKOF AT APPROX 100 KTS HAD THE FIRST OFFICER'S SEAT SLIDE BACKWARDS TO THE AFT STOPS.

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FO SEAT SLID BACK DURING TKOF ROLL AT APPROX 100 KTS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AIRPLANE WAS AN EMBRAER 145 AND HAS A FLEET PROB WITH COCKPIT SEAT FORE AND AFT POSITION LOCKING. THE RPTR SAID IN THIS INCIDENT THE SEAT LOCKING DEVICE WAS CHECKED TWICE; FIRST WHEN GETTING IN THE SEAT AND ADJUSTING THE FORE AND AFT POSITION AND SECONDLY ON TAXI OUT FORCE WAS EXERTED ON THE CTL COLUMN FORE AND AFT AND BOTH TIMES THE SEAT WAS CHECKED LOCKED. THE RPTR STATED SHE IS 5 FT 2 IN TALL AND POSITIONS THE SEAT TO THE MAX FORWARD POSITION AND ON TKOF ROLL SLIGHTLY BELOW 100 KNOTS THE SEAT MOVED RAPIDLY AFT TO THE REAR STOPS. THE RPTR SAID THE CAPT WAS THE PLT FLYING AND THE ONLY TASK THE RPTR COULD ACCOMPLISH WAS MAKE AIR TRAFFIC REPLIES. THE RPTR STATED THE ONLY CORRECTIVE ACTION ON THE SEAT LOCKING PROB SO FAR IS TO REQUIRE THE SEAT LOCK CHECK ON TAXI OUT. THE RPTR SAID THIS WAS THEIR FIRST SEAT LOCK PROB EXPERIENCE AND WAS A STARTLING SURPRISE!