Narrative:

After rolling out on a 10 mi final for what was going to be the ILS runway 36R at tulsa; we both noticed off flags for the GS. When the captain asked approach about this; they said they had been having problems with it lately. We quickly briefed up the necessary items for the localizer runway 36R; company procedures with myself accomplishing the landing. Visibility was at the approach minimums with moderate snowfall. After the FAF; I began a descent to the step-down altitude of 1300 ft MSL (MDA was 1060 ft). I forgot about the 1000 FPM descent rate restr below 1000 ft and continued to descend to the step-down altitude at 1200 FPM. As I began to leveloff; passing through about 1500 ft MSL; we received an 'obstacle; obstacle' caution from the GPWS. Since we were IMC I began to advance the thrust levers to go around when we received a 'pull up; pull up' warning. At this point I accomplished the terrain avoidance maneuver. I climbed about 1500 ft; no further warnings were received so I reduced my pitch and continued with normal go around procedures. At this point we had no contingency fuel left for another approach so we diverted to mci. After landing; we took a hard look at the approach plate; thinking maybe we had made a major mistake (ie; wrong altimeter settings; misread altitude restrs) but could find none. However; we did find the obstacle. It was a tower of 954 ft MSL just below and to the right of the final approach course. On our second attempt into tulsa about 2 hours later; I flew the same approach; but used about a 700 FPM descent rate so as to arrive at a point just prior to the step-down fix at 1300 ft MSL. We also wondered why there was about a 2 second gap between the 2 callouts made by the GPWS. We weren't sure whether we had received an obstacle caution and then an obstacle warning; or whether it was a warning with a long delay in the middle. This was my first time hearing the GPWS speak in flight; so I'm not sure if that is normal to have a delay between the 2 statements. First; it's possible that my descent rate of 1200 FPM below 1000 ft was just enough of a closure rate to set off the GPWS. Second; when briefing a non-precision approach; look at the obstacles that are causing you to have an altitude restr before descending to the MDA. Third; look at the descent rate necessary to arrive at your step-down altitude in a timely manner. It may be much less than our usual 1200 FPM. Supplemental information from acn 719052: I was focused on making the step-down fix and do not recall verbally calling the 1000 ft call.

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Original NASA ASRS Text

Title: B737-300 MAKING LOC APCH TO RWY 36R AT TUL MAKES GAR AFTER RECEIVING EGPWS OBSTACLE WARNING.

Narrative: AFTER ROLLING OUT ON A 10 MI FINAL FOR WHAT WAS GOING TO BE THE ILS RWY 36R AT TULSA; WE BOTH NOTICED OFF FLAGS FOR THE GS. WHEN THE CAPT ASKED APCH ABOUT THIS; THEY SAID THEY HAD BEEN HAVING PROBS WITH IT LATELY. WE QUICKLY BRIEFED UP THE NECESSARY ITEMS FOR THE LOC RWY 36R; COMPANY PROCS WITH MYSELF ACCOMPLISHING THE LNDG. VISIBILITY WAS AT THE APCH MINIMUMS WITH MODERATE SNOWFALL. AFTER THE FAF; I BEGAN A DSCNT TO THE STEP-DOWN ALT OF 1300 FT MSL (MDA WAS 1060 FT). I FORGOT ABOUT THE 1000 FPM DSCNT RATE RESTR BELOW 1000 FT AND CONTINUED TO DSND TO THE STEP-DOWN ALT AT 1200 FPM. AS I BEGAN TO LEVELOFF; PASSING THROUGH ABOUT 1500 FT MSL; WE RECEIVED AN 'OBSTACLE; OBSTACLE' CAUTION FROM THE GPWS. SINCE WE WERE IMC I BEGAN TO ADVANCE THE THRUST LEVERS TO GO AROUND WHEN WE RECEIVED A 'PULL UP; PULL UP' WARNING. AT THIS POINT I ACCOMPLISHED THE TERRAIN AVOIDANCE MANEUVER. I CLBED ABOUT 1500 FT; NO FURTHER WARNINGS WERE RECEIVED SO I REDUCED MY PITCH AND CONTINUED WITH NORMAL GAR PROCS. AT THIS POINT WE HAD NO CONTINGENCY FUEL LEFT FOR ANOTHER APCH SO WE DIVERTED TO MCI. AFTER LNDG; WE TOOK A HARD LOOK AT THE APCH PLATE; THINKING MAYBE WE HAD MADE A MAJOR MISTAKE (IE; WRONG ALTIMETER SETTINGS; MISREAD ALT RESTRS) BUT COULD FIND NONE. HOWEVER; WE DID FIND THE OBSTACLE. IT WAS A TWR OF 954 FT MSL JUST BELOW AND TO THE R OF THE FINAL APCH COURSE. ON OUR SECOND ATTEMPT INTO TULSA ABOUT 2 HRS LATER; I FLEW THE SAME APCH; BUT USED ABOUT A 700 FPM DSCNT RATE SO AS TO ARRIVE AT A POINT JUST PRIOR TO THE STEP-DOWN FIX AT 1300 FT MSL. WE ALSO WONDERED WHY THERE WAS ABOUT A 2 SECOND GAP BTWN THE 2 CALLOUTS MADE BY THE GPWS. WE WEREN'T SURE WHETHER WE HAD RECEIVED AN OBSTACLE CAUTION AND THEN AN OBSTACLE WARNING; OR WHETHER IT WAS A WARNING WITH A LONG DELAY IN THE MIDDLE. THIS WAS MY FIRST TIME HEARING THE GPWS SPEAK IN FLT; SO I'M NOT SURE IF THAT IS NORMAL TO HAVE A DELAY BTWN THE 2 STATEMENTS. FIRST; IT'S POSSIBLE THAT MY DSCNT RATE OF 1200 FPM BELOW 1000 FT WAS JUST ENOUGH OF A CLOSURE RATE TO SET OFF THE GPWS. SECOND; WHEN BRIEFING A NON-PRECISION APCH; LOOK AT THE OBSTACLES THAT ARE CAUSING YOU TO HAVE AN ALT RESTR BEFORE DSNDING TO THE MDA. THIRD; LOOK AT THE DSCNT RATE NECESSARY TO ARRIVE AT YOUR STEP-DOWN ALT IN A TIMELY MANNER. IT MAY BE MUCH LESS THAN OUR USUAL 1200 FPM. SUPPLEMENTAL INFO FROM ACN 719052: I WAS FOCUSED ON MAKING THE STEP-DOWN FIX AND DO NOT RECALL VERBALLY CALLING THE 1000 FT CALL.

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.