Narrative:

Aircraft was a 737-400 (which requires flaps 5 only takeoffs). On taxi out the first officer stated that due to weight and balance requirements we could only accomplish a flaps 1 takeoff. I looked down to the weight and balance screen on the ACARS and saw all blanks where the takeoff data should have been for flaps 5. It did not occur to me at that time we were on a 400 and what I was looking at was the flaps 15 section. During the normal taxi checks, I checked the takeoff warning horn and it sounded. We recycled everything (speed brake/flaps/slats and even parking brake). Obviously the horn continued to sound. I could not think of anything else so I returned to the gate. Maintenance worked on the aircraft for an hour and a half. They told us nothing. They signed the book off that the system checked out. At this point it still had not occurred to me the problem was that the aircraft was a 400. I told maintenance that after pushback I would start both engines and select flaps and see if we still had the horn. Obviously we still had the horn so I taxied back into the gate. The maintenance line crew stated that everything checked out normal for a 400. As soon as he said that both the first officer and myself realized what the problem was and continued on the trip. I contacted system dispatched en route and informed her what happened and said that I would call her on the ground in phoenix. As soon as we landed in phoenix, I called system and explained the entire situation to them. There was no damage to any equipment and no violations of any regulations or I would have contacted the chief pilot's office. That morning we departed denver airport in a 737- 300 bound for pittsburgh. The weight and balance required a flaps 1 takeoff. I never do flaps 1 takeoffs, unless required by the weight and balance, just to avoid this problem of confusion between the 300 and the 400. This was another heavy weight takeoff for a long flight. When I glanced down to the weight and balance screen, the area where the normal flaps 5 section was, was blank. (This was the flaps 15 section on the 400). Whenever there is confusion it is always best to analyze your assumptions. I should have taken the time to review the basic assumption that the first officer put to me which was that the weight and balance required a flaps 1 takeoff. The second thing I could have done was get the book and that might have triggered the realization as to what type of aircraft I was in. Supplemental information from acn 283597: our 737-300 and 737-400 cockpits look exactly the same from the pilot's seat. If the #300 (or 400 as appropriate) appeared on the flap handle of each aircraft, it would eliminate any possible confusion as to which model 737 a pilot is sitting in. I also think something could be done about the format of the ACARS weight and balance information. Presently, 300 takeoff page information lists flaps 1 information towards the top of the page with flaps 5 at the bottom of the page. The 400 takeoff page lists 5 information towards the top of the page and flaps 15 at the bottom of the page. As we fly 300's most of the time, it's not too difficult to be sitting in a 400 and mistake the takeoff information towards the top of the page for flaps 1 information. This problem could be eliminated by placing a statement just above the flaps 5 information on the 400 takeoff page that states 'flaps not authority/authorized.' implementing these 2 suggestions would do a lot to reduce potential confusion between the 2 737 models.

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Original NASA ASRS Text

Title: TKOF WARNING HORN ASSOCIATED WITH FLAP SETTING UNIQUE TO 737-400 MODEL HAD TO BE RESOLVED BY MAINT AFTER TAXI BACK TO GATE. PROB WITH FLC'S AWARENESS AND NOT WITH AIRPLANE. EMBARRASSING!

Narrative: ACFT WAS A 737-400 (WHICH REQUIRES FLAPS 5 ONLY TKOFS). ON TAXI OUT THE FO STATED THAT DUE TO WT AND BAL REQUIREMENTS WE COULD ONLY ACCOMPLISH A FLAPS 1 TKOF. I LOOKED DOWN TO THE WT AND BAL SCREEN ON THE ACARS AND SAW ALL BLANKS WHERE THE TKOF DATA SHOULD HAVE BEEN FOR FLAPS 5. IT DID NOT OCCUR TO ME AT THAT TIME WE WERE ON A 400 AND WHAT I WAS LOOKING AT WAS THE FLAPS 15 SECTION. DURING THE NORMAL TAXI CHKS, I CHKED THE TKOF WARNING HORN AND IT SOUNDED. WE RECYCLED EVERYTHING (SPD BRAKE/FLAPS/SLATS AND EVEN PARKING BRAKE). OBVIOUSLY THE HORN CONTINUED TO SOUND. I COULD NOT THINK OF ANYTHING ELSE SO I RETURNED TO THE GATE. MAINT WORKED ON THE ACFT FOR AN HR AND A HALF. THEY TOLD US NOTHING. THEY SIGNED THE BOOK OFF THAT THE SYS CHKED OUT. AT THIS POINT IT STILL HAD NOT OCCURRED TO ME THE PROB WAS THAT THE ACFT WAS A 400. I TOLD MAINT THAT AFTER PUSHBACK I WOULD START BOTH ENGS AND SELECT FLAPS AND SEE IF WE STILL HAD THE HORN. OBVIOUSLY WE STILL HAD THE HORN SO I TAXIED BACK INTO THE GATE. THE MAINT LINE CREW STATED THAT EVERYTHING CHKED OUT NORMAL FOR A 400. AS SOON AS HE SAID THAT BOTH THE FO AND MYSELF REALIZED WHAT THE PROB WAS AND CONTINUED ON THE TRIP. I CONTACTED SYS DISPATCHED ENRTE AND INFORMED HER WHAT HAPPENED AND SAID THAT I WOULD CALL HER ON THE GND IN PHOENIX. AS SOON AS WE LANDED IN PHOENIX, I CALLED SYS AND EXPLAINED THE ENTIRE SIT TO THEM. THERE WAS NO DAMAGE TO ANY EQUIP AND NO VIOLATIONS OF ANY REGS OR I WOULD HAVE CONTACTED THE CHIEF PLT'S OFFICE. THAT MORNING WE DEPARTED DENVER ARPT IN A 737- 300 BOUND FOR PITTSBURGH. THE WT AND BAL REQUIRED A FLAPS 1 TKOF. I NEVER DO FLAPS 1 TKOFS, UNLESS REQUIRED BY THE WT AND BAL, JUST TO AVOID THIS PROB OF CONFUSION BTWN THE 300 AND THE 400. THIS WAS ANOTHER HVY WT TKOF FOR A LONG FLT. WHEN I GLANCED DOWN TO THE WT AND BAL SCREEN, THE AREA WHERE THE NORMAL FLAPS 5 SECTION WAS, WAS BLANK. (THIS WAS THE FLAPS 15 SECTION ON THE 400). WHENEVER THERE IS CONFUSION IT IS ALWAYS BEST TO ANALYZE YOUR ASSUMPTIONS. I SHOULD HAVE TAKEN THE TIME TO REVIEW THE BASIC ASSUMPTION THAT THE FO PUT TO ME WHICH WAS THAT THE WT AND BAL REQUIRED A FLAPS 1 TKOF. THE SECOND THING I COULD HAVE DONE WAS GET THE BOOK AND THAT MIGHT HAVE TRIGGERED THE REALIZATION AS TO WHAT TYPE OF ACFT I WAS IN. SUPPLEMENTAL INFO FROM ACN 283597: OUR 737-300 AND 737-400 COCKPITS LOOK EXACTLY THE SAME FROM THE PLT'S SEAT. IF THE #300 (OR 400 AS APPROPRIATE) APPEARED ON THE FLAP HANDLE OF EACH ACFT, IT WOULD ELIMINATE ANY POSSIBLE CONFUSION AS TO WHICH MODEL 737 A PLT IS SITTING IN. I ALSO THINK SOMETHING COULD BE DONE ABOUT THE FORMAT OF THE ACARS WT AND BAL INFO. PRESENTLY, 300 TKOF PAGE INFO LISTS FLAPS 1 INFO TOWARDS THE TOP OF THE PAGE WITH FLAPS 5 AT THE BOTTOM OF THE PAGE. THE 400 TKOF PAGE LISTS 5 INFO TOWARDS THE TOP OF THE PAGE AND FLAPS 15 AT THE BOTTOM OF THE PAGE. AS WE FLY 300'S MOST OF THE TIME, IT'S NOT TOO DIFFICULT TO BE SITTING IN A 400 AND MISTAKE THE TKOF INFO TOWARDS THE TOP OF THE PAGE FOR FLAPS 1 INFO. THIS PROB COULD BE ELIMINATED BY PLACING A STATEMENT JUST ABOVE THE FLAPS 5 INFO ON THE 400 TKOF PAGE THAT STATES 'FLAPS NOT AUTH.' IMPLEMENTING THESE 2 SUGGESTIONS WOULD DO A LOT TO REDUCE POTENTIAL CONFUSION BTWN THE 2 737 MODELS.

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.