NMAC.

Narrative

AFTER PERFORMING EXTENSIVE MAINT ON A PA28-140 WHICH INCLUDED AN ANNUAL INSPECTION AND THE INSTALLATION OF A HIGHER HORSEPWR ENG (STC APPROVED); A TEST FLT WAS MADE. WX WAS CLR; GOOD VISIBILITY; WITH A THIN BROKEN STRATUS LAYER BTWN 1100 FT AND 1300 FT W OF THE ARPT -- PALOMAR (CRQ). ACFT WAS THOROUGHLY CHKED IN THE RUN UP AREA AND NO DISCREPANCIES WERE NOTED. ACFT DEPARTED VFR ON RWY 24 AND MADE L TFC; CLBING OUT OF THE PATTERN AND LEVELING OFF AT 5000 FT (IN CLASS E AIRSPACE); BUT CONTINUING A L PATTERN OVER THE ARPT SO THAT PERFORMANCE AND RELIABILITY CHKS COULD BE MADE ON THE NEW ENG CLOSE TO THE ARPT. TWR FREQ WAS MONITORED. SEVERAL CIRCUITS WERE MADE AROUND THE PATTERN. AFTER A TURN TO THE L XWIND WAS STARTED; A REQUEST TO THE TWR TO DSND INTO THE PATTERN WAS INITIATED. AT THIS INSTANT A MIL HELI (POSSIBLY A HUEY OR SIMILAR SIZE HELI) WAS SPOTTED IN VERY CLOSE PROX TO ACFT. THE HELI'S POS RELATIVE TO ACFT APPEARED TO BE SLIGHTLY TO THE R AND MAYBE 40-50 FT HIGHER AT A DISTANCE OF 300-400 FT CONVERGING HEAD ON. AN IMMEDIATE INCREASE TO THE L AND AN IMMEDIATE DSCNT WERE EXECUTED. IT APPEARED THAT THE HELI PERFORMED A SIMILAR MANEUVER; POSSIBLY CLBING INSTEAD OF DSNDING. AFTER A TURN TO THE L DOWNWIND; NOW AT ABOUT 4700 FT THE TWR INQUIRED AS TO WHETHER OR NOT VISUAL CONTACT WAS ESTABLISHED WITH THE HELI. A SAFE RETURN TO THE ARPT IN A L HAND PATTERN WAS MADE FOLLOWING A DSNDING R 360 DEGS MADE FROM THE L DOWNWIND IN ORDER TO LOSE ALT. AFTER A NORMAL LNDG; A VISIT TO THE TWR WAS MADE. IT WAS DETERMINED THAT THE HELI WAS IN CONTACT WITH APCH CTL. TYPE OF FLT (VFR OR IFR) IS UNKNOWN AT THIS TIME SO IT IS UNKNOWN AS TO WHETHER OR NOT HE RECEIVED ANY TA'S. AFTER DISCUSSING THE MATTER WITH THE 3 AIR TFC CTLRS ON DUTY AT THE FIELD AND THE TWR SUPVR; AND REFING NTSB 830 WHICH DOES NOT REQUIRE ANY RPTS TO BE FILED FOR AN OCCURRENCE OF THIS SORT; IT WAS DETERMINED THAT THE BEST COURSE OF ACTION BASED ON THE INFO WAS TO MAKE A RPT THROUGH THIS FORUM AS A PUBLIC SVC TO THE AVIATION COMMUNITY. CONTRIBUTING FACTORS MAY BE: MONITORING ENG AND FLT INSTS DURING POST MAINT TEST FLT. TFC SCAN INTERRUPTION AS A RESULT OF ATTEMPTING TO MAINTAIN ACCURATE TFC PATTERN LEGS AT ALT BY USING GND REF POINTS. NOT MONITORING APCH CTLR FREQ AND REQUESTING TA'S (ALTHOUGH NOT REQUIRED IN CLASS E AIRSPACE). FAILURE OR INABILITY OF APCH CTL TO ISSUE TA TO PLT OF HELI. FAILURE ON THE PART OF BOTH PLTS TO ADEQUATELY 'SEE AND AVOID.'