B757 TOOK OFF FROM LGA WITH WING FLAPS SET AT 5 DEGS RATHER THAN THE REQUIRED 15 DEGS.

Narrative

WE WERE SCHEDULED TO FLY FROM LGA TO DFW. WE HAD AN ACR INSPECTOR ON BOARD OBSERVING. PUSHBACK AND ENG START WERE NORMAL. I SET THE FLAPS AS WE STARTED TAXIING. TKOF NUMBERS CALLED FOR 15 DEG FLAPS. DURING THE TAXI AND BEFORE TKOF CHKS; I REMEMBER LOOKING AT THE FLAP HANDLE AND FLAP INDICATOR SEVERAL TIMES; BUT NOTICED NOTHING AMISS. THE CAPTAIN WAS VERY CONSCIENTIOUS IN CHKING FLAPS; BUT HE NOTICED NOTHING OUT OF THE ORDINARY EITHER (NOR DID THE FAA INSPECTOR). THERE WERE NO ACFT AHEAD OF US FOR THE RWY; SO DEP WAS FAIRLY QUICK; BUT NOT REALLY RUSHED; DUE TO ACFT LNDG ON THE CROSS RWY. TKOF ROLL; ROTATION; LIFT-OFF AND INITIAL CLB APPEARED NORMAL. AT 1000 FT AGL THE CAPT DIRECTED ME TO RAISE THE FLAPS FROM 15 DEGS TO 5 DEGS. AT THIS TIME I NOTICED THE FLAP HANDLE WAS ALREADY IN THE 5 DEGS DETENT. SINCE ACTUAL LIFT-OFF SPD WAS PROBABLY 10-15 KTS ABOVE COMPUTED V2; WE HAD NO ACFT INDICATIONS OF THE INCORRECT SETTING. I THINK THE REASON I SET THE FLAPS TO 5 DEGS WAS THAT FOR THE PREVIOUS 7 YRS I FLEW THE MD80 ACFT WHERE NORMAL TKOF FLAPS WERE THE SECOND DETENT ON THE FLAP LEVER (11 DEGS). ON THE B757 NORMAL TKOF FLAPS ARE THE THIRD DETENT (15 DEGS). SINCE I HAD FLOWN THE B757 ONLY ABOUT 1 1/2 MONTHS; I THINK I REVERTED TO MY OLD HABITS AND 'FEEL' FOR THE FLAP LEVER. THE REMAINDER OF THE FLT WAS THANKFULLY UNEVENTFUL.