A LNDG SF340 HAS TO GO AROUND AFTER EXPERIENCING A 30 DEG ROLL ON SHORT FINAL TO RWY 4L AT BOS. ALT WAS ABOUT 200- 300 FT AGL. FLT HAD BEEN GIVEN A LAHSO BUT HAD A DC10 ON FINAL TO RWY 4R AND A DC10 WITH PWR UP; HOLDING ON RWY 9 FOR AN IMMEDIATE DEP.

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LAHSO. WHILE ON APCH TO RWY 4L AT BOS; IT IS NOT UNCOMMON TO BE ABEAM OR SLIGHTLY BEHIND TO THE L OF A LARGE OR HVY ACFT. IT IS NOT UNCOMMON FOR THE PREVAILING WINDS TO BE OUT OF THE E; ALLOWING WINGTIP VORTICES (WAKE TURB) TO DRIFT INTO THE RWY 4L APCH COURSE. TWR ASSIGNS CLRNC 'XYZ123 YOU'RE CLRED TO LAND RWY 4L HOLD SHORT OF RWY 33R.' WHAT MAKES THIS SIT UNSAFE OR A HAZARD IS WHEN LCL TWR PUTS A LARGE OR HVY INTO POS ON RWY 9 AND IS TIMING THE RWY 9 DEP ON THE ARR OF RWY 4R. TYPICALLY; THE RWY 9 DEP IS SITTING 'READY TO GO; PWR UP' (MORE THAN IDLE). THE THRUST FROM THE RWY 9 DEP ALONG WITH THE DRIFTING WAKE FROM THE ARR ON RWY 4R; AND THE CLRNC TO LAHSO IS NOT AS SAFE AN OP AS THIS COULD BE. HVY ACFT RANGE FROM B757; B747; AIRBUS 330; DC10; B767; B777; L1011. WHAT MAKES THIS VERY INTERESTING IS WHEN THE RWY 9 DEP IS AN L1011 OR DC10; HIGH TAIL MOUNTED ENG. NO EASY ANSWER OTHER THAN GO AROUND. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT SAID THIS WAS AN SF340 AND THOUGHT THAT THIS WAS THE WORST OF ALL WORLDS FOR SMALLER LNDG ACFT. HE WANTED TO KNOW WHY ATC USUALLY PLACED THE HEAVIER ACFT ON THE R RWY. THIS SEQUENCE PLACED THE SMALLER ACFT ON THE DOWNWIND SIDE OF THE LARGER ACFT; EXPERIENCING THEIR WAKE TURB AND ALSO THE JETBLAST FROM RWY 9 TFC HOLDING FOR AN IMMEDIATE TKOF AFTER LNDG TFC RWY 4R. THE FO WAS FLYING THE ACFT BUT THE CAPT TOOK OVER AND PERFORMED THE GAR. THE TWR DOES NOT ISSUE ADVISORIES TO ACFT LNDG RWY 4L ABOUT THE JETBLAST POSSIBILITIES. THE CAPT WASN'T CERTAIN WHAT HE EXPERIENCED; JETBLAST OR WAKE TURB. HE FELT IT WAS A POSSIBLE COMBINATION OF BOTH. HE SENT IN A COMPANY RPT AND ONE TO HIS UNION SAFETY COMMITTEE. THEY SAID THEY WOULD TAKE THIS UP WITH THE TWR. THE LAHSO CLRNC SEEMED TO BE THE LESSER OF THE EVILS PRESENTED TO HIM ON THAT APCH.