Narrative:

During our descent into helena from the north on V21, we contacted helena tower and were cleared for a visual approach landing to runway 27. The tower asked us to report 10 mi north, which we did. They gave us a TA on a cessna which had departed runway 34 and was heading east. The advisory contained only a relative position (12 O'clock position), so we asked for his altitude. Since the cessna was not operating a transponder, he was not on our TCASII screen and the tower asked several times for more specific position and altitude information. He did not respond to several of these tower xmissions except to say his altitude was 5300 ft. So we leveled at 6000 ft and continued to search for him. The tower began to ask for his position relative to the smoke stacks 3 mi east of the runway 27 threshold. The cessna failed to respond to several of these requests, but then did give his position as '3 mi from the ridge line.' this ridge line is well east of the runway, so my copilot and I decided to continue our descent out of 6000 ft and begin our turn from a right base leg to final. As we did this, the copilot, who was flying, saw the cessna directly ahead approximately 1 mi, moving from right to left at or close to our altitude. He increased our angle of bank and our descent rate. We passed approximately 1/2 mi behind and 200 ft below the cessna and landed on runway 27. Supplemental information from acn 567257: I was on a return flight hln to M46. I received ATIS, then asked tower to taxi to active runway. Was told by tower that there was no wind or traffic and that I could take off on runway 34. I asked for a right turn after climb out, as I was eastbound. After climbing for 3 or 4 mins, I began getting a lot of popping, static, and parts of voice transmission from tower and other traffic, through my head phones. I wiggled the headphone cord where it goes into the ear cup and began to pick up parts of a conversation between hln tower and other traffic. Tower asked for my heading and elevation. I responded eastbound at 5300 ft. Tower then asked if I was north or south of extended centerline of runway 27. I responded that I was about on centerline, about 5 or 6 mi east of airport. Tower then said 'aircraft Y, turn right toward the south,' which I did. While in a right banked turn to the south, I first saw the air carrier flight, which was below and to the west of my position. The air carrier flight was in a r-hand descending turn to line up on final for runway 27. It should be noted that there was mist/haze in the area. Also, there was snow cover on the mountains and in the valley at the time. I did not, but should have had my transponder turned on so that the collision avoidance equipment on board the air carrier plane could have picked up my position. For corrective action, I intend to upgrade my radio gear by having a built-in intercom installed. Also, to purchase a new headset that has the latest active noise reduction features. I am not going to fly into any area requiring radio communication until the upgrades are complete.

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Original NASA ASRS Text

Title: A B737-300 CREW AND A C170 PLT HAD LESS THAN LEGAL SEPARATION IN HLN CLASS D AIRSPACE.

Narrative: DURING OUR DSCNT INTO HELENA FROM THE N ON V21, WE CONTACTED HELENA TWR AND WERE CLRED FOR A VISUAL APCH LNDG TO RWY 27. THE TWR ASKED US TO RPT 10 MI N, WHICH WE DID. THEY GAVE US A TA ON A CESSNA WHICH HAD DEPARTED RWY 34 AND WAS HEADING E. THE ADVISORY CONTAINED ONLY A RELATIVE POS (12 O'CLOCK POS), SO WE ASKED FOR HIS ALT. SINCE THE CESSNA WAS NOT OPERATING A XPONDER, HE WAS NOT ON OUR TCASII SCREEN AND THE TWR ASKED SEVERAL TIMES FOR MORE SPECIFIC POS AND ALT INFO. HE DID NOT RESPOND TO SEVERAL OF THESE TWR XMISSIONS EXCEPT TO SAY HIS ALT WAS 5300 FT. SO WE LEVELED AT 6000 FT AND CONTINUED TO SEARCH FOR HIM. THE TWR BEGAN TO ASK FOR HIS POS RELATIVE TO THE SMOKE STACKS 3 MI E OF THE RWY 27 THRESHOLD. THE CESSNA FAILED TO RESPOND TO SEVERAL OF THESE REQUESTS, BUT THEN DID GIVE HIS POS AS '3 MI FROM THE RIDGE LINE.' THIS RIDGE LINE IS WELL E OF THE RWY, SO MY COPLT AND I DECIDED TO CONTINUE OUR DSCNT OUT OF 6000 FT AND BEGIN OUR TURN FROM A R BASE LEG TO FINAL. AS WE DID THIS, THE COPLT, WHO WAS FLYING, SAW THE CESSNA DIRECTLY AHEAD APPROX 1 MI, MOVING FROM R TO L AT OR CLOSE TO OUR ALT. HE INCREASED OUR ANGLE OF BANK AND OUR DSCNT RATE. WE PASSED APPROX 1/2 MI BEHIND AND 200 FT BELOW THE CESSNA AND LANDED ON RWY 27. SUPPLEMENTAL INFO FROM ACN 567257: I WAS ON A RETURN FLT HLN TO M46. I RECEIVED ATIS, THEN ASKED TWR TO TAXI TO ACTIVE RWY. WAS TOLD BY TWR THAT THERE WAS NO WIND OR TFC AND THAT I COULD TAKE OFF ON RWY 34. I ASKED FOR A R TURN AFTER CLBOUT, AS I WAS EBOUND. AFTER CLBING FOR 3 OR 4 MINS, I BEGAN GETTING A LOT OF POPPING, STATIC, AND PARTS OF VOICE XMISSION FROM TWR AND OTHER TFC, THROUGH MY HEAD PHONES. I WIGGLED THE HEADPHONE CORD WHERE IT GOES INTO THE EAR CUP AND BEGAN TO PICK UP PARTS OF A CONVERSATION BTWN HLN TWR AND OTHER TFC. TWR ASKED FOR MY HDG AND ELEVATION. I RESPONDED EBOUND AT 5300 FT. TWR THEN ASKED IF I WAS N OR S OF EXTENDED CTRLINE OF RWY 27. I RESPONDED THAT I WAS ABOUT ON CTRLINE, ABOUT 5 OR 6 MI E OF ARPT. TWR THEN SAID 'ACFT Y, TURN R TOWARD THE S,' WHICH I DID. WHILE IN A R BANKED TURN TO THE S, I FIRST SAW THE ACR FLT, WHICH WAS BELOW AND TO THE W OF MY POS. THE ACR FLT WAS IN A R-HAND DSNDING TURN TO LINE UP ON FINAL FOR RWY 27. IT SHOULD BE NOTED THAT THERE WAS MIST/HAZE IN THE AREA. ALSO, THERE WAS SNOW COVER ON THE MOUNTAINS AND IN THE VALLEY AT THE TIME. I DID NOT, BUT SHOULD HAVE HAD MY XPONDER TURNED ON SO THAT THE COLLISION AVOIDANCE EQUIP ON BOARD THE ACR PLANE COULD HAVE PICKED UP MY POS. FOR CORRECTIVE ACTION, I INTEND TO UPGRADE MY RADIO GEAR BY HAVING A BUILT-IN INTERCOM INSTALLED. ALSO, TO PURCHASE A NEW HEADSET THAT HAS THE LATEST ACTIVE NOISE REDUCTION FEATURES. I AM NOT GOING TO FLY INTO ANY AREA REQUIRING RADIO COM UNTIL THE UPGRADES ARE COMPLETE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.