Clearance for air carrier light transport disputed.

Attributes
ACN	149161
Time
Date	199006
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : oxr
State Reference	CA
Altitude	msl bound lower : 4000 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ntd
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 400 flight time total : 4300 flight time type : 700
ASRS Report	149161
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	conflict : airborne less severe
Independent Detector	other flight crewa
Resolutory Action	none taken : unable
Consequence	Other
Miss Distance	vertical : 1000
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	other

Narrative:

On a flight from oxr to sfo in light transport X, we were flying runway heading to maintain 4000'. Switched frequencys to 124.7, mugu approach. Once contacted. Mugu instructed us, 'at the shoreline turn left heading 180 degrees, maintain 5000, company traffic light transport Y 12 O'clock, 3 mi and 5000'.' at this point we maintained 4000' as originally cleared. Mugu then instructed several other aircraft. As we did not have a chance to acknowledge the clearance, the heading we were on brought us right under the company light transport Y at 5000'. When we were able to question the original clearance as to why he cleared us to maintain 5000', he insisted he did not clear us to maintain 5000'. There was no conflict or any violations. The potential for a conflict was ever present had we flown the altitude cleared. This controller was very, very busy with aircraft.

Original NASA ASRS Text

Title: CLRNC FOR ACR LTT DISPUTED.

Narrative: ON A FLT FROM OXR TO SFO IN LTT X, WE WERE FLYING RWY HDG TO MAINTAIN 4000'. SWITCHED FREQS TO 124.7, MUGU APCH. ONCE CONTACTED. MUGU INSTRUCTED US, 'AT THE SHORELINE TURN LEFT HDG 180 DEGS, MAINTAIN 5000, COMPANY TFC LTT Y 12 O'CLOCK, 3 MI AND 5000'.' AT THIS POINT WE MAINTAINED 4000' AS ORIGINALLY CLRED. MUGU THEN INSTRUCTED SEVERAL OTHER ACFT. AS WE DID NOT HAVE A CHANCE TO ACKNOWLEDGE THE CLRNC, THE HDG WE WERE ON BROUGHT US RIGHT UNDER THE COMPANY LTT Y AT 5000'. WHEN WE WERE ABLE TO QUESTION THE ORIGINAL CLRNC AS TO WHY HE CLRED US TO MAINTAIN 5000', HE INSISTED HE DID NOT CLR US TO MAINTAIN 5000'. THERE WAS NO CONFLICT OR ANY VIOLATIONS. THE POTENTIAL FOR A CONFLICT WAS EVER PRESENT HAD WE FLOWN THE ALT CLRED. THIS CTLR WAS VERY, VERY BUSY WITH ACFT.

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.