HELI ON TEST FLT HAS PLT DOOR POP OPEN. CLRED TO LAND AND RETURN TO FBO. CONCERNED REF DOOR TEARING OFF; TOUCHED DOWN ON RWY; CLOSED DOOR; THEN HOVER TAXIED TO FBO.

Narrative

I WAS PIC ON A ROUTINE MAINT FLT IN A HELI; FLYING OUT OF SEE IN EL CAJON; CA. ON BOARD THE ACFT WAS OUR CREW CHIEF; A LICENSED A AND P MECH; AS WE WERE CONDUCTING FORWARD FLT (MAIN ROTOR) TRACK AND BAL VIBRATION ANALYSIS; AND CREW CHIEF WAS OPERATING THE BALANCING EQUIP WHILE I WAS FLYING. WE HAD BEEN WORKING ON THIS PARTICULAR ACFT THE DAY BEFORE; AS WELL AS HAD MADE SEVERAL FLTS ON THIS PARTICULAR MORNING; WORKING TO FINISH THE HIGH-SPD TRACK AND BAL CHK. WE HAD REQUESTED THE USE OF RWY 17/35 (TO AVOID THE FLOW OF FIXED-WING TFC) AND REQUESTED OVERFLT OF THE ARPT AT 900 FT MSL; FOR N AND SBOUND PASSES. THE TWR ADVISED US TO RPT ON THE 180 TURN EACH PASS; AND THAT WE WERE CLRED TO PROCEED WITH OUR MAINT FLT. THIS WAS ONE OF MANY FLTS WE HAD MADE THAT MORNING; AND WE HAD BEEN USING THE 'NUMBERS XY' TO STAGE OUR DEPS AND ARRS FROM. (THE 'NUMBERS XY' IS NEAR THE FBO AND IS COMMONLY USED BY US FOR AN INGRESS AND EGRESS RTE TO THE FBO AS THERE ARE TIMES WE HAVE TO DO PROLONGED HOVER CHKS; AND THIS KEEPS ANY BLOWING DUST AWAY FROM OTHER FBO'S ON THE FIELD). WE WERE HEADED NBOUND AND AS WE WERE ABOUT TO TURN 180 SBOUND; MY PLT'S DOOR POPPED OPEN IN FLT. THE TWR FREQ WAS REALLY BUSY AT THAT POINT; AND WE PROCEEDED WITH OUR TURN AND FINALLY GOT THROUGH TO THE TWR AND ADVISED THEM THAT WE NEEDED TO CANCEL OUR OVERFLT REQUEST; AND WERE INSTEAD REQUESTING A RETURN FOR LNDG RIGHT AWAY. THE TWR CLRED US TO THE FBO (BY WAY OF 17/35) AND AS WE SLOWED AND APCHED A HOVER; MY PLT'S DOOR BEGAN TO FULLY OPEN FROM THE ROTOR DOWNWASH; AND BOTH ME AND MY CREW CHIEF'S CONCERN WAS THE DOOR WOULD OPEN 180 DEGS; AND TEAR OFF; OR DO DAMAGE TO THE MAIN WINDSHIELD; SO I ELECTED TO SET THE ACFT DOWN IMMEDIATELY ON RWY 17/35 (NEAR THE NUMBERS 35). I PULLED THE DOOR SHUT AND AGAIN SAFE-LOCKED IT; WITH REASSURANCE FROM MY CREW CHIEF THAT HE'D LOOK AT IT AS SOON AS WE GOT BACK TO THE FBO. WE CALLED THE TWR AND THEY ADVISED US THAT WE WERE CLRED TO LAND AT THE FBO AND I ADVISED THEM THAT WE HAD A DOOR POP OPEN ON THE LAST RUN THAT WE HAD TO SECURE IT IMMEDIATELY BEFORE PROCEEDING.