RPTR IN JETSTAR II ENCOUNTERS B757 WAKE TURB OVER THE NUMBERS JUST BEFORE TOUCHDOWN PROVOKING A BALKED LNDG.

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WE WERE EXECUTING THE RIVER VISUAL APCH ON RWY 18 AT DCA. THE CONDITIONS WERE VMC AT NIGHT WITH THE WINDS RPTED FROM THE S AT 7 KTS. WE WERE VECTORED ON THE APCH AND ADVISED WE WERE 4.3 MI IN TRAIL OF AN ACR B757. BY LISTENING TO THE FREQ IT APPEARED THAT THE B757 WAS HAVING DIFFICULTY GETTING DOWN IN TIME FOR THE APCH. WE DISCUSSED FOLLOWING THE B757 AND WERE PREPARED FOR WAKE TURB. NO WAKE TURB WAS ENCOUNTERED DURING THE APCH. AT 50-75 FT AGL OF THE RWY WE WERE STARTING TO FLARE. WE WERE AT VREF OF 140 KTS AND MAX LNDG WT OF 36000 LBS. AT THIS POINT WE FELT TURB IN THE MANNER OF LIGHT TO MODERATE CHOP AND THEN HAD AN UNCOMMANDED ROLL TO THE R. IT REQUIRED FULL AILERON AND RUDDER DEFLECTION TO ARREST THE ROLL. WE EXECUTED A FULL PWR GAR AND CLRED THE TURB IN ABOUT 100 FT OF CLB. DUE TO THE NATURE OF THE RIVER APCH AT NIGHT IT IS DIFFICULT AT BEST TO DETERMINE THE TOUCHDOWN POINT OF THE ACFT AHEAD. WE STAYED ON THE VASI TO THE FLARE. OTHER THAN INCREASE SEPARATION AND NORMAL WAKE AVOIDANCE I CAN OFFER NO SOLUTION TO THIS PROB. I WOULD HESITATE TO LAND AT NIGHT AT MAX LNDG WT ONLY TO FIND A BRAKE OR THRUST REVERSE FAILURE UPON TOUCHDOWN. IN ANY CASE; THE CONFIGN THAT WE WERE IN; GEAR DOWN; FLAPS FULL; MAX LNDG WT; AND THRUST COMING TO IDLE; ALONG WITH CLOSE PROX TO THE GND; WAS THE WORST PLACE FOR THIS ENCOUNTER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE ENCOUNTERED A NIBBLE TYPE TURB AND CAME UP WITH THE PWR. THEN THERE WAS A SINKER. THEN HE COMMENCED A GAR. THEN THERE WAS A 35-40 DEG UNCOMMANDED ROLL. FORTUNATELY; THE JETSTAR II HAS 4 FAN ENGS TO PWR OUT OF THE WAKE ENCOUNTER. THE RPTR STATED THE 4 FAN ENGS ARE THE DIFFERENCE BTWN THE JETSTAR I WHICH DOES NOT HAVE FAN ENGS AND THE JETSTAR II. THE RPTR STATED HE WOULD LIKE TO KNOW HIS INTERVAL IN TIME BEHIND A WAKE THREATENING ACFT.