Small aircraft observed another aircraft in close proximity while in the traffic pattern.

Attributes
ACN	109646
Time
Date	198904
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : rhv
State Reference	CA
Altitude	msl bound lower : 700 msl bound upper : 700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : rhv
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	other
Flight Plan	None
Aircraft 2
Operator	general aviation : personal
Make Model Name	Helicopter
Flight Phase	cruise other
Flight Plan	None
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 35 flight time total : 1025 flight time type : 1000
ASRS Report	109646
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private
Events
Anomaly	conflict : nmac non adherence : far
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 100
Supplementary
Primary Problem	Flight Crew Human Performance

Narrative:

Clearance from controller was: 'cleared to left base, #2 cleared to land runway 13L.' additional traffic, a helicopter transiting to south along highway 680. During descent on left base, I saw flash of stripes on rotor below and at my 2-3 O'clock position, converging with my aircraft from right to left. I flattened (leveled off) my descent and lost sight of the helicopter. I next saw the helicopter flash by immediately below and to my left. I landed routinely and after some thought, contacted tower personnel. They stated they did not see helicopter and that he was routed '680-101' for transition. Subsequent tape examination showed that controller erred in not specifically routing helicopter as he had stated. Primary cause, I believe to be, controller error, compounded by helicopter operator's failure to challenge a vague transition clearance and further to negligently enter the air traffic area in opp direction on the downwind for runway 13L.

Original NASA ASRS Text

Title: SMA OBSERVED ANOTHER ACFT IN CLOSE PROX WHILE IN THE TRAFFIC PATTERN.

Narrative: CLRNC FROM CTLR WAS: 'CLRED TO LEFT BASE, #2 CLRED TO LAND RWY 13L.' ADDITIONAL TFC, A HELI TRANSITING TO S ALONG HWY 680. DURING DSCNT ON LEFT BASE, I SAW FLASH OF STRIPES ON ROTOR BELOW AND AT MY 2-3 O'CLOCK POS, CONVERGING WITH MY ACFT FROM RIGHT TO LEFT. I FLATTENED (LEVELED OFF) MY DSCNT AND LOST SIGHT OF THE HELI. I NEXT SAW THE HELI FLASH BY IMMEDIATELY BELOW AND TO MY LEFT. I LANDED ROUTINELY AND AFTER SOME THOUGHT, CONTACTED TWR PERSONNEL. THEY STATED THEY DID NOT SEE HELI AND THAT HE WAS ROUTED '680-101' FOR TRANSITION. SUBSEQUENT TAPE EXAMINATION SHOWED THAT CTLR ERRED IN NOT SPECIFICALLY ROUTING HELI AS HE HAD STATED. PRIMARY CAUSE, I BELIEVE TO BE, CTLR ERROR, COMPOUNDED BY HELI OPERATOR'S FAILURE TO CHALLENGE A VAGUE TRANSITION CLRNC AND FURTHER TO NEGLIGENTLY ENTER THE ATA IN OPP DIRECTION ON THE DOWNWIND FOR RWY 13L.

Data retrieved from NASA's ASRS site as of August 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.