Small aircraft entering traffic pattern with proper announcements has near midair collision on final...

Attributes
ACN	187987
Time
Date	199109
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : 2v2
State Reference	CO
Altitude	agl bound lower : 200 agl bound upper : 600
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	descent : approach landing : go around
Flight Plan	VFR
Aircraft 2
Make Model Name	Small Transport
Flight Phase	descent : approach landing : go around
Route In Use	approach : straight in approach : visual
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial
Experience	flight time last 90 days : 18 flight time total : 2355 flight time type : 18
ASRS Report	187987
Person 2
Affiliation	Other
Function	other personnel
Qualification	other other : other
Events
Anomaly	aircraft equipment problem : less severe conflict : nmac other spatial deviation
Independent Detector	other other : unspecified cockpit
Resolutory Action	flight crew : took evasive action none taken : insufficient time
Consequence	Other
Miss Distance	horizontal : 0 vertical : 250
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was returning from cross country. I had been released by denver departure controller after transiting the TCA. I tuned to longmont unicom and heard no traffic. I called longmont unicom for landing advisory and received same. I announced my turn to downwind. On downwind I noticed an aircraft that seemed to be over the cement plant in lyons, co, turning toward boulder, co. At this point my radio's became very noisy. I asked unicom if the aircraft over lyons was landing at longmont. I heard no reply (radios still very noisy). I announced my turn to base leg and to final. About 1000 ft from touchdown a twin engine airplane flew under me. I applied power and did a 360 degree turn (about 200 ft MSL). The twin retracted its gear and climbed out on runway heading. I completed my 360, announced on final and landed. I lost sight of the twin and have no idea where it went. I believe the contributing factors were: 1) the twin turned to final too far from the end of the runway. 2) my radios didn't allow me to hear the twin's transmissions.

Original NASA ASRS Text

Title: SMA ENTERING TFC PATTERN WITH PROPER ANNOUNCEMENTS HAS NMAC ON FINAL.

Narrative: I WAS RETURNING FROM XCOUNTRY. I HAD BEEN RELEASED BY DENVER DEP CTLR AFTER TRANSITING THE TCA. I TUNED TO LONGMONT UNICOM AND HEARD NO TFC. I CALLED LONGMONT UNICOM FOR LNDG ADVISORY AND RECEIVED SAME. I ANNOUNCED MY TURN TO DOWNWIND. ON DOWNWIND I NOTICED AN ACFT THAT SEEMED TO BE OVER THE CEMENT PLANT IN LYONS, CO, TURNING TOWARD BOULDER, CO. AT THIS POINT MY RADIO'S BECAME VERY NOISY. I ASKED UNICOM IF THE ACFT OVER LYONS WAS LNDG AT LONGMONT. I HEARD NO REPLY (RADIOS STILL VERY NOISY). I ANNOUNCED MY TURN TO BASE LEG AND TO FINAL. ABOUT 1000 FT FROM TOUCHDOWN A TWIN ENG AIRPLANE FLEW UNDER ME. I APPLIED PWR AND DID A 360 DEG TURN (ABOUT 200 FT MSL). THE TWIN RETRACTED ITS GEAR AND CLBED OUT ON RWY HDG. I COMPLETED MY 360, ANNOUNCED ON FINAL AND LANDED. I LOST SIGHT OF THE TWIN AND HAVE NO IDEA WHERE IT WENT. I BELIEVE THE CONTRIBUTING FACTORS WERE: 1) THE TWIN TURNED TO FINAL TOO FAR FROM THE END OF THE RWY. 2) MY RADIOS DIDN'T ALLOW ME TO HEAR THE TWIN'S TRANSMISSIONS.

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.