Narrative:

This situation happened on an IFR flight from lax to oak. The aircraft was an large transport freighter on which I was the F/east. The captain was at the controls for this leg of the flight. The first officer was handling the communications. We were being vectored to the ILS 11 approach at oak. We were in IMC, moderate turbulence and rain. We had been cleared to 4000' MSL by the approach controller. Closer to the field we were cleared lower (I did not hear the altitude) and I heard the first officer read back our new vector and that we were out of 4000' for 2000'. At 3000' the first officer checked with the captain if 2000' was indeed the correct altitude (we were still about 14-15 mi from the field). The captain nodded 'yes.' the first officer then turned to me and asked if 2000' was what I had heard. I said, 'I don't know.' at this time we were passing approximately 2500'. At 2400' the ground proximity warning system activated, saying, 'terrain, pull up.' the captain applied climb power and immediately initiated a climb. We climbed to 3000', then told the controller that we were climbing back to 4000'. The controller asked if we had descended below 3000'. We said yes, that we had been assigned 2000' and that was what we had read back. The controller said ok, that we would be cleared to 2000' in a few more miles. Supplemental information from acn 105733: working on the back side of the clock is tough. Tough for the pilots and controllers. Everyone is tired. Mistakes will be made. Increased vigilance and communication is a must.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR LGT ALT DEVIATION OVERSHOT CFIT DURING DURING RADAR VECTOR FOR IAP ILS APCH INTO OAK RWY 11.

Narrative: THIS SITUATION HAPPENED ON AN IFR FLT FROM LAX TO OAK. THE ACFT WAS AN LGT FREIGHTER ON WHICH I WAS THE F/E. THE CAPT WAS AT THE CONTROLS FOR THIS LEG OF THE FLT. THE F/O WAS HANDLING THE COMS. WE WERE BEING VECTORED TO THE ILS 11 APCH AT OAK. WE WERE IN IMC, MODERATE TURB AND RAIN. WE HAD BEEN CLRED TO 4000' MSL BY THE APCH CTLR. CLOSER TO THE FIELD WE WERE CLRED LOWER (I DID NOT HEAR THE ALT) AND I HEARD THE F/O READ BACK OUR NEW VECTOR AND THAT WE WERE OUT OF 4000' FOR 2000'. AT 3000' THE F/O CHKED WITH THE CAPT IF 2000' WAS INDEED THE CORRECT ALT (WE WERE STILL ABOUT 14-15 MI FROM THE FIELD). THE CAPT NODDED 'YES.' THE F/O THEN TURNED TO ME AND ASKED IF 2000' WAS WHAT I HAD HEARD. I SAID, 'I DON'T KNOW.' AT THIS TIME WE WERE PASSING APPROX 2500'. AT 2400' THE GND PROX WARNING SYS ACTIVATED, SAYING, 'TERRAIN, PULL UP.' THE CAPT APPLIED CLB PWR AND IMMEDIATELY INITIATED A CLB. WE CLBED TO 3000', THEN TOLD THE CTLR THAT WE WERE CLBING BACK TO 4000'. THE CTLR ASKED IF WE HAD DSNDED BELOW 3000'. WE SAID YES, THAT WE HAD BEEN ASSIGNED 2000' AND THAT WAS WHAT WE HAD READ BACK. THE CTLR SAID OK, THAT WE WOULD BE CLRED TO 2000' IN A FEW MORE MILES. SUPPLEMENTAL INFO FROM ACN 105733: WORKING ON THE BACK SIDE OF THE CLOCK IS TOUGH. TOUGH FOR THE PLTS AND CTLRS. EVERYONE IS TIRED. MISTAKES WILL BE MADE. INCREASED VIGILANCE AND COM IS A MUST.

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.