CAPT OF AN MLG ON A 'PROVING TEST' FLT; WITH THE FAA INSPECTORS ABOARD; TOOK EVASIVE ACTION IN RESPONSE TO A TCASII RA DURING FINAL ON SIDE BY SIDE VISUAL APCH TO PARALLEL RWYS.

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DURING THE EVENT DESCRIBED BELOW I WAS PIC; OCCUPYING THE L SEAT AND FLYING THE ACFT; WHILE A COMPANY CHK AIRMAN WAS IN THE R SEAT. AN FAA OBSERVER WAS SITTING IN 1 OF THE COCKPIT JUMPSEATS AND A COMPANY FO WAS IN THE OTHER. 3 COMPANY FLT ATTENDANTS WERE IN THE CABIN WITH MORE FAA OBSERVERS. THE PURPOSE OF THE FLT WAS A COMPANY PROVING RUN. WHILE INBOUND TO STAPLETON INTL ARPT; DENVER FROM THE NW ON THE DEN R313 DEGS; SOMEWHERE INSIDE OF DRAKO INTXN (DEN 313033); DENVER APCH VECTORED US TO THE NE OF THE ARPT. WE WERE TOLD TO EXPECT A VISUAL APCH TO RWY 26L AND BEGAN CONFIGURING TO FLAPS 5; 170 KIAS (APPROX); AS WE CONTINUED OUR DSCNT TO AN ASSIGNED ALT OF 8000 FT. WHILE STILL MANEUVERING TO THE NE OF THE FIELD ON ESSENTIALLY AN EXTENDED R BASE TO RWY 26L; DENVER APCH TOLD US TO NOW EXPECT A VISUAL APCH TO RWY 26R; INFORMING US THAT A (ACR Y) ACFT WOULD BE LNDG RWY 26L. I VISUALLY LOCATED THE (ACR Y) TFC IN THE DISTANCE; APPROX 10 O'CLOCK; APPEARING TO MANEUVER ON EXTENDED FINAL. TO THE BEST OF MY RECOLLECTION WE RELAYED THIS TFC IN SIGHT; WERE TOLD THAT THE (ACR Y) TFC ALSO HAD US IN SIGHT; AND WHILE STILL WELL OUTSIDE OF ALTUR WERE CLRED FOR THE VISUAL APCH TO RWY 26R. THE (ACR Y) TFC WAS STILL IN SIGHT (NOW APPROX 11:30 O'CLOCK) WHEN I BEGAN A R HAND DSNDING TURN FROM BASE/DOGLEG ONTO THE VISUAL EXTENDED CTRLINE OF RWY 26R. IT APPEARED TO ME THAT WHEN WE ROLLED OUT ON FINAL WE WOULD BE NEARLY ABEAM OUR TFC ON PARALLEL APCHS. DURING OUR TURN TO FINAL THE (ACR Y) TFC WAS MOMENTARILY OUT OF SIGHT (STILL TO OUR L AND BELOW US) WHEN OUR TCASII GAVE US A TA. MY FO AND I WERE REASONABLY SURE THAT IT WAS THE PRESENCE OF THE (ACR Y) TFC THAT TRIGGERED THE TA; AND I WAS NOT OVERLY CONCERNED AT THIS POINT. NEVERTHELESS; IN AGREEMENT WITH MY FO; I INCREASED THE BANK ANGLE OF MY R HAND TURN TO FINAL TO ENSURE GREATER SEPARATION WITH OUR PARALLELING (ACR Y) TFC. I ATTEMPTED TO REACQUIRE VISUAL CONTACT WITH THE TARGET AND PREPARED TO MANEUVER IF THE TA WERE TO CHANGE INTO A RA. SECONDS AFTER THE TA ALERT; AND NEARING ROLLOUT ON FINAL TO RWY 26R; OUR TCASII ISSUED AN RA COMMANDING A CLB. I IMMEDIATELY INITIATED THE VERT MANEUVER DIRECTED BY THE RA/VSI; SMOOTHLY BUT FIRMLY ARRESTING OUR SHALLOW DSCNT AND ESTABLISHING THE REQUIRED CLB. DURING THIS MANEUVER PRECIPITATED BY THE RA; THE FAA JUMPSEAT OBSERVER BECAME BELLIGERENT AND BEGAN SHOUTING LOUD OBSCENITIES. HIS EXTREMELY DISRUPTIVE OUTBURST DURING NOT ONLY THE 'STERILE COCKPIT' ENVIRONMENT BUT DURING A SENSITIVE RA DIRECTED MANEUVER POSED A SIGNIFICANT AND DANGEROUS DISTR AND WAS DETRIMENTAL TO SAFETY OF FLT. I GLANCED BACK BRIEFLY TO DETERMINE IF HE NEEDED TO BE RESTRAINED. NEVERTHELESS; I MAINTAINED ACFT CTL AND AFTER NO MORE THAN 200 FT OF CLB THE RA ADVISED 'CLR OF CONFLICT.' I NOW VISUALLY ACQUIRED THE PARALLELING TFC AHEAD OF US; LATERALLY SEPARATED TO OUR L; AND BELOW US. A NORMAL VISUAL APCH TO RWY 26R WAS RESUMED TO AN UNEVENTFUL LNDG. ALTHOUGH MY FO AND I WERE MONITORING BOTH THE ALTUR NDB AND DEN VOR; THERE IS NO PRECISION COURSE GUIDANCE TO RWY 26R. PRECISE VISUAL EXTENDED CTRLINE LINEUP ESPECIALLY AT NIGHT IS DIFFICULT. WITH RWY 26L AND RWY 26R SEPARATED BY LESS THAN 800 FT; EVEN MINOR DEVS R OR L OF CTRLINE ON FINAL BECOME SIGNIFICANT ESPECIALLY WHEN PARALLEL TFC ROLLS OUT ABEAM. IN MY OPINION; I DID NOT DEV S OF THE RWY 26R VISUAL FINAL GND TRACK PARAMETERS AT ANY TIME DURING THE APCH. AT NO TIME DID THE COMPANY JUMPSEAT OBSERVER NOR THE COMPANY CHK AIRMAN ACTING AS FO BELIEVE THAT A DANGEROUS TCASII THREAT EXISTED. AT NO TIME DURING THIS MANEUVER DID THE COMPANY CHK AIRMAN TAKE CTL OF THE ACFT.