MIL HELI ON GCA APCH HAS NMAC WITH SMA.

Narrative

NAVY HELI WAS UNDER GCA CTL AT NAS WILLOW GROVE; PA. WE WERE ON BASE LEG HDG 060 AT 2000 FT MSL AT 90 KTS. GCA ADVISED US OF TFC AT 11 O'CLOCK AND 2 MI. WE NATURALLY LOOKED AND SAW NOTHING (WE DID NOTE TFC LATER AT 4000- 5000 FT OVER 3 MI IN THAT POS HDG AWAY). WE WERE TURNED ONTO 'FAC' AT 350 DEG HDG AND WERE STILL AT 2000 FT WHEN WE RECEIVED ANOTHER TFC CALL AT 9 O'CLOCK. I NOTED TFC AT 8-9 O'CLOCK AT 'ABOUT' OUR SAME ALT. WE WERE THEN 'ON GS' AND BEGAN DSCNT. WITH THE DISTR I MAY HAVE STAYED 'SLIGHTLY ABOVE GS' BUT WAS ABOUT 4 MI FROM LNDG AT 1700 FT WHEN GCA ASKED IF WE 'HAD THE TFC AT 9 O'CLOCK'. LOOKING L (I WAS IN THE L SEAT) I NOTED THAT TFC NOW AT LESS THAN A MI AT OUR ALT IN MY ESTIMATION. I LOWERED THE COLLECTIVE WATCHING THE TFC CLOSE US AND PASS OVER OUR POS WITH 300-400 FT OF CLRNC MAX (ACFT PASSED 50 FT BEHIND US). HAVING JUST COMPLETED A BAY FORMATION TRAINING FLT I FEEL CONFIDENT IN MY CLOSURE AND DISTANCE ESTIMATES. HAD I NOT REACTED; I FEEL THERE WOULD HAVE BEEN A MIDAIR ACCIDENT. AFTER LNDG I CONTACTED THE TCA CTLR AND TWR SUPVR. TWR INDICATED THE TFC WAS OUT OF NE PHILADELPHIA ARPT VFR AND HAD US 'IN SIGHT'. THEY NOTED NO MODE C ALT READOUT. IF THE SMA HAD US VISUALLY WHY DIDN'T THEY CLB? WHY DIDN'T THEY CHANGE HDGS TO PASS WELL BEHIND US SO AS NOT TO CONFLICT WITH OUR GND CTLED APCH? 1) ENSURE BETTER COORD BTWN NE PHILADELPHIA TWR AND NAS WILLOW GROVE TO ENSURE ADEQUATE SEPARATION WHEN OPERATING RWY 33 OPS. 2) REQUIRE ADEQUATE CHK OF MODE C IN TCA BY 'PLTS' PRIOR TO TKOF. 3) REQUIRE RADAR CTL OF ALL ACFT OUT OF NE PHILADELPHIA WHEN THEY LAUNCH N INTO RWY 33 AT NAS WILLOW GROVE. 4) A LOT OF TFC ON A CLR NIGHT CAN BECOME CONFUSING. THINGS FARTHER AWAY COULD BE CONFUSED WITH CLOSER TFC CALLS. CITY LIGHT CAN CONFUSE LOW TFC. I DON'T THINK THE SMA HAD US AT ALL.