Narrative:

We were on the grandpa-one RNAV arrival. We were cleared to (if I remember right) 5100 ft. We had continuous moderate turbulence and very gusty winds. Around 5 mi out before trrop intersection; we broke out of the clouds and the captain wanted me to call the airport. I did; and we were 'cleared the visual approach to runway 19C; but keep tracking the grandpa-one arrival.' captain immediately dialed in 4100 ft on the altitude window. (By our company procedure; I; the PNF; should have dialed all new altitudes. But there are no IFR approachs to runway 19L or runway 19R. By doing what he did; and sticking in an altitude; he sort of took me by surprise. If he had let me do it; I would have used the class B chart altitudes.) anyway; he slowly descended to 4100 ft; and approach said 'low altitude alert; do you have the terrain in sight?' I said; 'we did;' and it was at our 2:30-3 O'clock position; about 3 mi away. I told the captain; you went below the class B airspace. From here; we made a normal approach and landing. No egpws went off. What caused this: 1) we were tired. Our 1ST day ended as a very late pm trip; and by day 3 (this day); this day turned into an early am trip. 2) captain should have let me dial in the altitudes; and say something if he is doing something non-standard. 3) I wished I had double-checked the altitude he threw in; with class B chart. Normally I religiously try to be very careful about the class B airspace. I forgot to challenge him on the altitude; and verify. Why? Tired. The constant moderate turbulence made me focus on the las airport. I will be very careful for this in the future.

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Original NASA ASRS Text

Title: B737-700 FLT WAS CLEARED FOR A VISUAL APCH. ATC ISSUED A LOW ALT ALERT AS THE FLT MANEUVERED FOR THE APCH.

Narrative: WE WERE ON THE GRANDPA-ONE RNAV ARR. WE WERE CLRED TO (IF I REMEMBER RIGHT) 5100 FT. WE HAD CONTINUOUS MODERATE TURB AND VERY GUSTY WINDS. AROUND 5 MI OUT BEFORE TRROP INTXN; WE BROKE OUT OF THE CLOUDS AND THE CAPT WANTED ME TO CALL THE ARPT. I DID; AND WE WERE 'CLRED THE VISUAL APCH TO RWY 19C; BUT KEEP TRACKING THE GRANDPA-ONE ARR.' CAPT IMMEDIATELY DIALED IN 4100 FT ON THE ALT WINDOW. (BY OUR COMPANY PROC; I; THE PNF; SHOULD HAVE DIALED ALL NEW ALTS. BUT THERE ARE NO IFR APCHS TO RWY 19L OR RWY 19R. BY DOING WHAT HE DID; AND STICKING IN AN ALT; HE SORT OF TOOK ME BY SURPRISE. IF HE HAD LET ME DO IT; I WOULD HAVE USED THE CLASS B CHART ALTS.) ANYWAY; HE SLOWLY DSNDED TO 4100 FT; AND APCH SAID 'LOW ALT ALERT; DO YOU HAVE THE TERRAIN IN SIGHT?' I SAID; 'WE DID;' AND IT WAS AT OUR 2:30-3 O'CLOCK POS; ABOUT 3 MI AWAY. I TOLD THE CAPT; YOU WENT BELOW THE CLASS B AIRSPACE. FROM HERE; WE MADE A NORMAL APCH AND LNDG. NO EGPWS WENT OFF. WHAT CAUSED THIS: 1) WE WERE TIRED. OUR 1ST DAY ENDED AS A VERY LATE PM TRIP; AND BY DAY 3 (THIS DAY); THIS DAY TURNED INTO AN EARLY AM TRIP. 2) CAPT SHOULD HAVE LET ME DIAL IN THE ALTS; AND SAY SOMETHING IF HE IS DOING SOMETHING NON-STANDARD. 3) I WISHED I HAD DOUBLE-CHKED THE ALT HE THREW IN; WITH CLASS B CHART. NORMALLY I RELIGIOUSLY TRY TO BE VERY CAREFUL ABOUT THE CLASS B AIRSPACE. I FORGOT TO CHALLENGE HIM ON THE ALT; AND VERIFY. WHY? TIRED. THE CONSTANT MODERATE TURB MADE ME FOCUS ON THE LAS ARPT. I WILL BE VERY CAREFUL FOR THIS IN THE FUTURE.

Data retrieved from NASA's ASRS site as of January 2009 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.