C152 PLT RPTS NMAC WITH FLT OF 2 MIL HELI'S IN THE VICINITY OF HILL MOA.

Narrative

NEAR MISS OCCURRED IN CLASS E AIRSPACE WHILE I WAS IN CRUISING FLT AT 1800 FT ON AN EASTERLY HDG (APPROX 100 DEGS) OVER THE RAPPAHANNOCK RIVER ABOUT 3 MI E OF SHANNON ARPT (EZF); FREDERICKSBURG; VA (NEAR THE 200 DEG RADIAL OF BROOKE VOR ABOUT 7 MI BELOW THE STATION). I SUDDENLY SPOTTED A MIL HELI ON MY L AT A HORIZ DISTANCE OF ABOUT 2000 FT ABOUT TO INTERSECT MY COURSE AT CLOSE TO A 90-100 DEG ANGLE. VERT SEPARATION WAS OBVIOUSLY SUFFICIENT TO AVOID COLLISION; BUT DISTURBINGLY CLOSE AND DIFFICULT TO JUDGE ACCURATELY; POSSIBLY IN THE VICINITY OF 200 FT. I COULD DETECT NO EVASIVE ACTION BY THE HELI AND IMMEDIATELY BEGAN A FULL PWR CLB TO INCREASE THE VERT SEPARATION. THE HELI QUICKLY PASSED UNDER THE REAR OF MY AIRPLANE. I THEN OBSERVED A SECOND HELI IN TRAIL; BUT SUFFICIENTLY FAR BACK THAT HE WOULD PASS BEHIND ME AT A SAFE DISTANCE. LOOKING OVER MY R SHOULDER I DETERMINED BOTH HAD PASSED BEYOND MY AIRPLANE AND APPEARED TO BE CONTINUING ON COURSE. SUDDENLY; THE SECOND HELI INITIATED A L TURN AND TOOK AN INTERCEPTION HDG TOWARD ME. AFTER OVERTAKING ME THE PLT SLOWED TO MY SPD AND HELD A PARALLEL COURSE ABOUT 150 FT OFF MY R SIDE AND TO THE IMMEDIATE REAR OF MY AIRPLANE. I MONITORED 121.5; ANTICIPATING A CALL; BUT NONE CAME. AFTER 1-2 MINS HE ABRUPTLY TERMINATED THE INTERCEPTION WITH A R TURN BACK TOWARD HIS ORIGINAL HDG. I CAN ONLY PRESUME HE WAS ATTEMPTING TO IDENT MY N NUMBER (PERHAPS NOT POSSIBLE BECAUSE OF 3 INCH NUMBERS ON THIS OLDER CESSNA). I WAS MAINTAINING A VIGILANT SCAN SO WAS SHOCKED BY THE UNEXPECTED ENCOUNTER. APPARENTLY; THE PLT ALSO FAILED TO SEE ME IN A TIMELY MANNER. THIS SEEMS TO BE SIMPLY AN UNFORTUNATE SIT IN WHICH THE HUMAN EYE MOMENTARILY FAILED BOTH OF US.