Aircraft descended below assigned altitude.

Attributes
ACN	134797
Time
Date	199001
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : san
State Reference	CA
Altitude	msl bound lower : 4000 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : san
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 180 flight time total : 16000 flight time type : 2100
ASRS Report	134797
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

While en route from lax to san we received a clearance to descend to 8000'. This was acknowledged and indicated. At approximately 10,000' (after sometime during which ATC had conversations with other aircraft) we received a call to 'continue descent at our discretion to plan the visual approach to 27.' I responded that we would continue our descent and keep it coming on down. At approximately 4000' we were asked to confirm our altitude. I did and was told that our last clearance was to 8000'. My reply was that our last clearance was to 'continue our descent at our discretion.' ATC disputed this and gave us a clearance to climb to 5000' and if there need be further discussion to call on the ground. We complied and landed normally. Feeling we did not do anything wrong I did call approach for clarification. After I explained my understanding, I, in turn, was told that the instructions to continue descent at our discretion (no altitude restrictions) 'implied' that we did not have to slow to 250 KTS below 10,000' because we were more than 3 mi off shore. A clearance with that kind of thinking under the circumstances should have never been given. The supervisor on duty agreed totally saying he would talk to his controller. I was assured by him that we had no conflict and in fact was sorry for the situation.

Original NASA ASRS Text

Title: ACFT DESCENDED BELOW ASSIGNED ALT.

Narrative: WHILE ENRTE FROM LAX TO SAN WE RECEIVED A CLRNC TO DSND TO 8000'. THIS WAS ACKNOWLEDGED AND INDICATED. AT APPROX 10,000' (AFTER SOMETIME DURING WHICH ATC HAD CONVERSATIONS WITH OTHER ACFT) WE RECEIVED A CALL TO 'CONTINUE DSCNT AT OUR DISCRETION TO PLAN THE VISUAL APCH TO 27.' I RESPONDED THAT WE WOULD CONTINUE OUR DSCNT AND KEEP IT COMING ON DOWN. AT APPROX 4000' WE WERE ASKED TO CONFIRM OUR ALT. I DID AND WAS TOLD THAT OUR LAST CLRNC WAS TO 8000'. MY REPLY WAS THAT OUR LAST CLRNC WAS TO 'CONTINUE OUR DSCNT AT OUR DISCRETION.' ATC DISPUTED THIS AND GAVE US A CLRNC TO CLIMB TO 5000' AND IF THERE NEED BE FURTHER DISCUSSION TO CALL ON THE GND. WE COMPLIED AND LANDED NORMALLY. FEELING WE DID NOT DO ANYTHING WRONG I DID CALL APCH FOR CLARIFICATION. AFTER I EXPLAINED MY UNDERSTANDING, I, IN TURN, WAS TOLD THAT THE INSTRUCTIONS TO CONTINUE DSCNT AT OUR DISCRETION (NO ALT RESTRICTIONS) 'IMPLIED' THAT WE DID NOT HAVE TO SLOW TO 250 KTS BELOW 10,000' BECAUSE WE WERE MORE THAN 3 MI OFF SHORE. A CLRNC WITH THAT KIND OF THINKING UNDER THE CIRCUMSTANCES SHOULD HAVE NEVER BEEN GIVEN. THE SUPVR ON DUTY AGREED TOTALLY SAYING HE WOULD TALK TO HIS CTLR. I WAS ASSURED BY HIM THAT WE HAD NO CONFLICT AND IN FACT WAS SORRY FOR THE SITUATION.

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.