B777 in ZOA's airspace begins descent issued to company aircraft with similar call sign.

Attributes
ACN	613021
Time
Date	200404
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : oal.vortac
State Reference	NV
Altitude	msl single value : 31000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa.artcc tower : smf.tower
Operator	common carrier : air carrier
Make Model Name	B777-200
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level descent : vacating altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise : level descent : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 200 flight time total : 16000 flight time type : 2000
ASRS Report	613021
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : published procedure non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	controller : separated traffic controller : issued advisory controller : issued new clearance
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

As captain, I was making a PA announcement and off the radio. First officer was taking ATC calls. When I finished and told the first officer that I was back with him, he said that we had been cleared to FL240. Just then, ATC called and asked what altitude we were descending to. First officer said FL240 and ATC said that was for another aircraft, but no problem, descend now to FL280. We did and there were no further problems. First officer told me he had read back FL240 with our call sign and that ATC had not corrected anything at that time. There was another company flight with a similar call sign on the air at that time and this was no doubt part of the problem.

Original NASA ASRS Text

Title: B777 IN ZOA'S AIRSPACE BEGINS DSCNT ISSUED TO COMPANY ACFT WITH SIMILAR CALL SIGN.

Narrative: AS CAPT, I WAS MAKING A PA ANNOUNCEMENT AND OFF THE RADIO. FO WAS TAKING ATC CALLS. WHEN I FINISHED AND TOLD THE FO THAT I WAS BACK WITH HIM, HE SAID THAT WE HAD BEEN CLRED TO FL240. JUST THEN, ATC CALLED AND ASKED WHAT ALT WE WERE DSNDING TO. FO SAID FL240 AND ATC SAID THAT WAS FOR ANOTHER ACFT, BUT NO PROB, DSND NOW TO FL280. WE DID AND THERE WERE NO FURTHER PROBS. FO TOLD ME HE HAD READ BACK FL240 WITH OUR CALL SIGN AND THAT ATC HAD NOT CORRECTED ANYTHING AT THAT TIME. THERE WAS ANOTHER COMPANY FLT WITH A SIMILAR CALL SIGN ON THE AIR AT THAT TIME AND THIS WAS NO DOUBT PART OF THE PROB.

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.