Small transport took evasive action to avoid an small aircraft due to clearance problem.

Attributes
ACN	105656
Time
Date	198903
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : pom
State Reference	CA
Altitude	msl bound lower : 4300 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa
Operator	common carrier : air carrier
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent other
Route In Use	enroute airway : ont
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 3300 flight time type : 1500
ASRS Report	105656
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 2050 flight time type : 300
ASRS Report	106191
Events
Anomaly	conflict : nmac non adherence : published procedure non adherence : required legal separation
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 400 vertical : 300
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

We had been cleared to descend to 4000' from 6000' MSL. At about 4300' and 4 east of pom 070 degree right we encountered a wbound airplane (small aircraft) at approximately our altitude. After initiating a slight descending right turn, we asked the ont approach controller if he saw any traffic there. He told us we had been cleared to descend to 4000' and then he had cleared us to climb and maintain 5000' due to that traffic. Neither myself nor the first officer heard him give us the amended clearance to climb back to 5000', and neither of us acknowledged receiving such a clearance. We told the controller this, and he said to climb and maintain 5000', which we did. However by now, this traffic was no longer a factor. If in fact the controller did issue the amended clearance, neither crew member heard it, nor acknowledged on the radio, its receipt.

Original NASA ASRS Text

Title: SMT TOOK EVASIVE ACTION TO AVOID AN SMA DUE TO CLRNC PROBLEM.

Narrative: WE HAD BEEN CLRED TO DSND TO 4000' FROM 6000' MSL. AT ABOUT 4300' AND 4 E OF POM 070 DEG R WE ENCOUNTERED A WBOUND AIRPLANE (SMA) AT APPROX OUR ALT. AFTER INITIATING A SLIGHT DSNDING RIGHT TURN, WE ASKED THE ONT APCH CTLR IF HE SAW ANY TFC THERE. HE TOLD US WE HAD BEEN CLRED TO DSND TO 4000' AND THEN HE HAD CLRED US TO CLB AND MAINTAIN 5000' DUE TO THAT TFC. NEITHER MYSELF NOR THE F/O HEARD HIM GIVE US THE AMENDED CLRNC TO CLB BACK TO 5000', AND NEITHER OF US ACKNOWLEDGED RECEIVING SUCH A CLRNC. WE TOLD THE CTLR THIS, AND HE SAID TO CLB AND MAINTAIN 5000', WHICH WE DID. HOWEVER BY NOW, THIS TFC WAS NO LONGER A FACTOR. IF IN FACT THE CTLR DID ISSUE THE AMENDED CLRNC, NEITHER CREW MEMBER HEARD IT, NOR ACKNOWLEDGED ON THE RADIO, ITS RECEIPT.

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.