SMA HAS NMAC ON PRACTICE ILS APCH CIRCLE TO LAND.

Narrative

WE HAD JUST BEEN CLRED FOR THE PRACTICE ILS 11 APCH CIRCLE TO RWY 5 FOR LNDG AT BED ARPT BY BOSTON APCH AND WERE INSTRUCTED BY BED TWR TO RPT BREAKING OFF AT APPROX 2 MI PRIOR TO ENTERING THE L DOWNWIND TO RWY 5 DUE TO THE INCREASED TFC IN THE PATTERN. AS WE BEGAN OUR R TURN FOR THE L DOWNWIND FOR RWY 5; WE WERE TOLD THAT WE WOULD BE '#4 FOR THE ARPT FOLLOWING AN SMA X ON A STRAIGHT IN VISUAL APCH TO RWY 5.' I PICKED OUT THE 2 SMA Y'S ON FINAL AND THEN IT SEEMED LIKE 20 SECONDS BEFORE WE PICKED OUT THE SMA X WHO MUCH TO OUR SURPRISE; WAS FLYING DIRECT TO THE NUMBERS (TO RWY 5) AND HAD SUBSEQUENTLY CROSSED THE DOWNWIND TFC INCLUDING US TO GET THERE. THE SMA X WAS ON WHAT SEEMED LIKE A HEAD-ON COLLISION COURSE TO US AND IF IT WEREN'T FOR OUR SWIFT EVASIVE MANEUVERS; IT MIGHT HAVE ENDED IN TRAGEDY. THE SMA Y DID NOT TAKE ANY EVASIVE ACTIONS TO MISS US AND I QUESTION IF THE PLT WAS EVEN AWARE OF HIS EXACT POS RELATIVE TO US AT THE TIME OF THE OCCURRENCE. THEN; WHEN WE WERE ESTABLISHED ON FINAL FOR RWY 5; AT APPROX 1 MI OUT; HANSCOM TWR THEN INSTRUCTED US TO TURN R TO ENTER THE L DOWNWIND FOR RWY 29; WHICH WE DID PROMPTLY. AT THE MID-FIELD; BED TWR ADVISED US TO 'SQUAWK 1200; BOSTON APCH WAS ABOUT TO HAVE A HEART ATTACK!' APPARENTLY (AND I CAN ONLY ASSUME); THE BOSTON APCH CTLR SAW THE WHOLE SCENE ON HIS RADAR SCREEN AND HE REALIZED THAT HE WAS VIRTUALLY PWRLESS TO PREVENT IT. HOWEVER; BED TWR DOES HAVE A D-BRITE RADAR SCREEN IN THE TWR AND MIGHT HAVE BEEN ABLE TO PREVENT THIS 'NEAR MISS' (I HOPE). MAYBE THE ANSWER IS TO SEE IF THAT TYPE OF RADAR CAN BE ENHANCED ENOUGH TO MAKE SURE THAT THE ENTIRE TFC PATTERN FLOW IS MUCH MORE EASILY SEEN ON SCREEN FOR THE SAFETY OF ALL WHO FLY. WHEN THE TFC PATTERN STARTS TO GET QUITE BUSY; I SUSPECT THAT THE TWR CTLR WOULD WELCOME ANY AID OR DEVICE TO MAKE THEIR DIFFICULT JOB THAT MUCH EASIER.