B737 inbound to oak runway 11 experienced GPWS because of misunderstanding of ATC assigned altitude.

Attributes
ACN	598776
Time
Date	200311
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : oak.airport
State Reference	CA
Altitude	msl bound lower : 2100 msl bound upper : 3100
Environment
Flight Conditions	IMC
Weather Elements	Ice
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : nct.tracon
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	descent : approach descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 80 flight time total : 5000 flight time type : 3000
ASRS Report	598776
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : ground less severe non adherence : clearance
Independent Detector	aircraft equipment : gpws other controllera other flight crewa
Resolutory Action	controller : issued advisory flight crew : took evasive action
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	ATC Human Performance

Narrative:

On approach into oakland runway 11, base leg, 4000 ft MSL, talking to approach control. Captain and I noted the controller being hard to understand. The controller has an asian accent with a speech impediment. Soon after noting this, we were told to descend to 2100 ft MSL. We descended to this altitude. The altitude was read back to the controller as '2100.' after arriving at 2100 ft, a terrain warning from the GPWS went off. The captain took evasive action and climbed, at the same time the controller called to confirm that we were at 3100 ft. I told him we were in the climb to 3100 ft but were told 2100 ft and read back 2100 ft. The controller didn't make any comment after this, and sent us to tower. The remainder of this was uneventful. This controller may have said 3100 ft, but due to his speech, I had heard 2100. I would have verified, but in my mind there was no question as to what I heard. I have heard this controller several times, and have discussed this controller's speech with other capts as being difficult to understand.

Original NASA ASRS Text

Title: B737 INBOUND TO OAK RWY 11 EXPERIENCED GPWS BECAUSE OF MISUNDERSTANDING OF ATC ASSIGNED ALT.

Narrative: ON APCH INTO OAKLAND RWY 11, BASE LEG, 4000 FT MSL, TALKING TO APCH CTL. CAPT AND I NOTED THE CTLR BEING HARD TO UNDERSTAND. THE CTLR HAS AN ASIAN ACCENT WITH A SPEECH IMPEDIMENT. SOON AFTER NOTING THIS, WE WERE TOLD TO DSND TO 2100 FT MSL. WE DSNDED TO THIS ALT. THE ALT WAS READ BACK TO THE CTLR AS '2100.' AFTER ARRIVING AT 2100 FT, A TERRAIN WARNING FROM THE GPWS WENT OFF. THE CAPT TOOK EVASIVE ACTION AND CLBED, AT THE SAME TIME THE CTLR CALLED TO CONFIRM THAT WE WERE AT 3100 FT. I TOLD HIM WE WERE IN THE CLB TO 3100 FT BUT WERE TOLD 2100 FT AND READ BACK 2100 FT. THE CTLR DIDN'T MAKE ANY COMMENT AFTER THIS, AND SENT US TO TWR. THE REMAINDER OF THIS WAS UNEVENTFUL. THIS CTLR MAY HAVE SAID 3100 FT, BUT DUE TO HIS SPEECH, I HAD HEARD 2100. I WOULD HAVE VERIFIED, BUT IN MY MIND THERE WAS NO QUESTION AS TO WHAT I HEARD. I HAVE HEARD THIS CTLR SEVERAL TIMES, AND HAVE DISCUSSED THIS CTLR'S SPEECH WITH OTHER CAPTS AS BEING DIFFICULT TO UNDERSTAND.

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.