On north downwind vector to oak ILS runway 11 by nct approach control, a B737-300 flight crew read b...

Attributes
ACN	598640
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 : 3000
Environment
Flight Conditions	IMC
Weather Elements	Rain Turbulence
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
Navigation In Use	ils localizer & glide slope : 295
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 255 flight time total : 20000 flight time type : 10000
ASRS Report	598640
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : overshoot non adherence : clearance non adherence : published procedure other anomaly other other spatial deviation
Independent Detector	aircraft equipment : gpws other flight crewa
Resolutory Action	controller : issued new clearance flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were being vectored to runway 11 at oak. We were at 4000 ft on downwind to the ILS to runway 11 northeast of the field. We thought the controller said descend to 2100 ft. We were about abeam the OM for the approach. The first officer read back 2100 ft and I started to descend to 2100 ft. The minimum altitude for that area is about 3800 ft, but we were about to turn toward the FAF and we were under his control. At 2100 ft we received a 'terrain, terrain, pull up.' I immediately executed a climb and was climbing through 3000 ft when the controller asked us to confirm that we were at '3100 ft.' we told him that we were leveling off from a climb from 2100 ft and we understood that he had given us a descent to 2100 ft and had read that back to him. He told us to turn and descend to 2000 ft until localizer intercept and then intercept the GS at 1800 ft. Approach and landing was uneventful. This controller talked with a speech impediment and when he spoke fast it was difficult to understand him. Why he didn't correct us when we read back the wrong altitude, I don't know. He was busy. After we had our problem, he did slow his speech down and it was easier to understand. I should have questioned him further on the 2100 ft instruction because it was an odd altitude with that minimum sector altitude. Callback conversation with reporter revealed the following information: captain said that he waited a bit too long to challenge the descent clearance, especially knowing that he was heading for higher terrain. By the time it bothered him sufficiently to question ATC, the reporter advised the GPWS was alarming. The other principle problem was the controller's speech rate. It was very fast and appeared to have an impediment. After the controller questioned the flight crew's descent altitude, and the captain's challenge response, the controller's speech rate slowed down sufficiently to be understood.

Original NASA ASRS Text

Title: ON N DOWNWIND VECTOR TO OAK ILS RWY 11 BY NCT APCH CTL, A B737-300 FLT CREW READ BACK INCORRECT DSCNT ALT RESULTING IN A GPWS ALERT CLB.

Narrative: WE WERE BEING VECTORED TO RWY 11 AT OAK. WE WERE AT 4000 FT ON DOWNWIND TO THE ILS TO RWY 11 NE OF THE FIELD. WE THOUGHT THE CTLR SAID DSND TO 2100 FT. WE WERE ABOUT ABEAM THE OM FOR THE APCH. THE FO READ BACK 2100 FT AND I STARTED TO DSND TO 2100 FT. THE MINIMUM ALT FOR THAT AREA IS ABOUT 3800 FT, BUT WE WERE ABOUT TO TURN TOWARD THE FAF AND WE WERE UNDER HIS CTL. AT 2100 FT WE RECEIVED A 'TERRAIN, TERRAIN, PULL UP.' I IMMEDIATELY EXECUTED A CLB AND WAS CLBING THROUGH 3000 FT WHEN THE CTLR ASKED US TO CONFIRM THAT WE WERE AT '3100 FT.' WE TOLD HIM THAT WE WERE LEVELING OFF FROM A CLB FROM 2100 FT AND WE UNDERSTOOD THAT HE HAD GIVEN US A DSCNT TO 2100 FT AND HAD READ THAT BACK TO HIM. HE TOLD US TO TURN AND DSND TO 2000 FT UNTIL LOC INTERCEPT AND THEN INTERCEPT THE GS AT 1800 FT. APCH AND LNDG WAS UNEVENTFUL. THIS CTLR TALKED WITH A SPEECH IMPEDIMENT AND WHEN HE SPOKE FAST IT WAS DIFFICULT TO UNDERSTAND HIM. WHY HE DIDN'T CORRECT US WHEN WE READ BACK THE WRONG ALT, I DON'T KNOW. HE WAS BUSY. AFTER WE HAD OUR PROB, HE DID SLOW HIS SPEECH DOWN AND IT WAS EASIER TO UNDERSTAND. I SHOULD HAVE QUESTIONED HIM FURTHER ON THE 2100 FT INSTRUCTION BECAUSE IT WAS AN ODD ALT WITH THAT MINIMUM SECTOR ALT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CAPT SAID THAT HE WAITED A BIT TOO LONG TO CHALLENGE THE DSCNT CLRNC, ESPECIALLY KNOWING THAT HE WAS HEADING FOR HIGHER TERRAIN. BY THE TIME IT BOTHERED HIM SUFFICIENTLY TO QUESTION ATC, THE RPTR ADVISED THE GPWS WAS ALARMING. THE OTHER PRINCIPLE PROB WAS THE CTLR'S SPEECH RATE. IT WAS VERY FAST AND APPEARED TO HAVE AN IMPEDIMENT. AFTER THE CTLR QUESTIONED THE FLT CREW'S DSCNT ALT, AND THE CAPT'S CHALLENGE RESPONSE, THE CTLR'S SPEECH RATE SLOWED DOWN SUFFICIENTLY TO BE UNDERSTOOD.

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.

On north downwind vector to oak ILS runway 11 by nct approach control, a B737-300 flight crew read back incorrect descent altitude resulting in a GPWS alert climb.