Air carrier large transport misunderstood clearance and descended below assigned altitude.

Attributes
ACN	93250
Time
Date	198808
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ork
State Reference	AZ
Altitude	msl bound lower : 23100 msl bound upper : 24000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zab
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other descent 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 : 78 flight time total : 10000 flight time type : 750
ASRS Report	93250
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 17000 flight time type : 1000
ASRS Report	93598
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Were issued a descent to FL240 before reaching FL240, were issued a clearance to 17000' which we repeated back to center. Passing through approximately 23800' with a high rate of descent 2000 FPM to get through WX, we were told to turn and maintain FL240. We stopped descent at 23100' and climbed back to FL240. We questioned center about clearance to 17000' and he responded we were not cleared to that altitude but we had repeated the clearance to 17000' to center when it was issued west/O any response from center. No conflict was made known to us. The only comment from center was 'are you climbing back to FL240?' we were handed off to the next sector west/O further comment from center. Supplemental information from acn 93598: there was another aircraft with call sign similar to ours and we were in severe WX conditions navigation with radar and instrument.

Original NASA ASRS Text

Title: ACR LGT MISUNDERSTOOD CLRNC AND DESCENDED BELOW ASSIGNED ALT.

Narrative: WERE ISSUED A DSCNT TO FL240 BEFORE REACHING FL240, WERE ISSUED A CLRNC TO 17000' WHICH WE REPEATED BACK TO CENTER. PASSING THROUGH APPROX 23800' WITH A HIGH RATE OF DSCNT 2000 FPM TO GET THROUGH WX, WE WERE TOLD TO TURN AND MAINTAIN FL240. WE STOPPED DSCNT AT 23100' AND CLBED BACK TO FL240. WE QUESTIONED CENTER ABOUT CLRNC TO 17000' AND HE RESPONDED WE WERE NOT CLRED TO THAT ALT BUT WE HAD REPEATED THE CLRNC TO 17000' TO CENTER WHEN IT WAS ISSUED W/O ANY RESPONSE FROM CENTER. NO CONFLICT WAS MADE KNOWN TO US. THE ONLY COMMENT FROM CENTER WAS 'ARE YOU CLBING BACK TO FL240?' WE WERE HANDED OFF TO THE NEXT SECTOR W/O FURTHER COMMENT FROM CENTER. SUPPLEMENTAL INFO FROM ACN 93598: THERE WAS ANOTHER ACFT WITH CALL SIGN SIMILAR TO OURS AND WE WERE IN SEVERE WX CONDITIONS NAVIGATION WITH RADAR AND INSTRUMENT.

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.