Narrative:

Since nov/thur/02 aircraft X has had six occurrences of trailing edge flaps not extending properly. Five of these occurrences were during the approach phase of flight, the remaining single incident occurring during taxi for takeoff. Here is a brief description of the events as they occurred: nove/thur/02, during the approach, the flaps would not extend with normal flap handle movement. Using the alternate flap extension method, the leading edge flaps and slats extended normally, but the trailing edges flaps remained up. An emergency was declared by the captain and the landing was made with flaps 1 uneventfully. The alternate system overrides asymmetric indication, so we suspected there was a mechanical lockout condition. The flaps were inspected for obvious defects, along with the torque tubes and transfer gearboxes. The flap position transmitters were inspected and the position indicator was replaced as a precaution. Nov/fri/02, much like the previous day, the flaps would not extend when the flap handle was moved to position 1 during the approach. The flap handle was cycled back to 0 and again to 1, this time with normal results. Flaps 30 was selected and the landing was uneventful. Alternate flaps extension was not used and no emergency was declared. Again, the trailing edge flaps system was inspected for any visual binding or defects. The overhead P5 flight control panel was replaced (from where the alternate flaps are operated), along with the right flap position transmitter (though, as stated previously, an erroneous asymmetry indication is not likely to be the cause with the information known). The alternate flap drive motor was also replaced at this time for the following reason: if the cause of this problem was indeed asymmetry indication, then the alternate flap extension method should have driven the trailing edge flaps to the desired setting in on the earlier occasion, and a weak motor may have been the cause. Dec/sun/02, during taxi for takeoff, the flaps would not extend. The aircraft returned to the gate and mechanics replaced the trailing edge flap position indicator (the second in four days). An operational check was performed and the flaps worked normally. Flight approach phase again, flap extension failed in normal. Alternate procedures were used and the landing was uneventful with no emergency declared. After another visual inspection of the flap system, all jackscrew reservoirs were serviced with no reports of dry or low levels. The flap control cable tensions and tension loss switch were checked, along with the flap bypass shutoff valve (which supplies or removes hydraulic power from the flap drive motor in alternate operation or asymmetric conditions). The flap/slat indication module was replaced as a precaution (this unit was rts'd yesterday since it is not a part of the trailing edge flap asymmetry protection). The flaps were operated extensively and no further defects were found. Dec/mon/02, during approach the flaps would not extend normally. Alternate flaps were used and landed safely with flaps 15. An emergency was not declared. Field tech, was called in to assist with the troubleshooting efforts immediately identified a corroded connector for the right flap position transmitter as well as another at a junction box in the wheel well. Aside from the initial write-up in on thur, all other failures were overridden with use of alternate flaps. At this point, with the possibility that the flight crew may have made an error in the use of the alternate flaps procedure, and with this new finding, the focus was again shifted to the indication system and a subsequent erroneous asymmetry lockout condition. The two connectors were replaced and the system operationally checked satisfactorily. Due to the history over the holiday weekend, however, was requested to also check the fluid levels of all eight flap xmissions and jackscrews. The #5 and #6 xmissions were found to be under serviced, but with no evidence of past or present leakage. They were serviced to the proper level and the flaps were checked one last time with no defects. Only one flight was madebefore the flaps failed to extend, yet again, on approach to alternate flaps were again used to extend the flaps to 15 and landing was uneventful with no emergency declared. Field tech, was also called in to assist with the troubleshooting efforts. #5 and #6 flap xmissions were again checked and #5 was found to be low, in fact, at only 1/3 full. The #4 and #5 flap xmissions were replaced and the flap system was inspected and operationally checked again, with no defects found. A functional check flight was arranged and performed with several apches and flap cycles. The aircraft was returned to service this afternoon and has operated one revenue flight with no further problems reported.

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Original NASA ASRS Text

Title: A B737-300 HAD 6 OCCURRENCES OF TRAILING EDGE FLAPS FAILING TO EXTEND ON APCH. NUMEROUS PARTS REPLACED. FOUND FLAP #4 AND #5 FLAP JACKSCREW AND XMISSION TORQUE LIMITER FAILED.

Narrative: SINCE NOV/THUR/02 ACFT X HAS HAD SIX OCCURRENCES OF TRAILING EDGE FLAPS NOT EXTENDING PROPERLY. FIVE OF THESE OCCURRENCES WERE DURING THE APCH PHASE OF FLT, THE REMAINING SINGLE INCIDENT OCCURRING DURING TAXI FOR TKOF. HERE IS A BRIEF DESCRIPTION OF THE EVENTS AS THEY OCCURRED: NOVE/THUR/02, DURING THE APCH, THE FLAPS WOULD NOT EXTEND WITH NORMAL FLAP HANDLE MOVEMENT. USING THE ALTERNATE FLAP EXTENSION METHOD, THE LEADING EDGE FLAPS AND SLATS EXTENDED NORMALLY, BUT THE TRAILING EDGES FLAPS REMAINED UP. AN EMER WAS DECLARED BY THE CAPT AND THE LNDG WAS MADE WITH FLAPS 1 UNEVENTFULLY. THE ALTERNATE SYSTEM OVERRIDES ASYMMETRIC INDICATION, SO WE SUSPECTED THERE WAS A MECHANICAL LOCKOUT CONDITION. THE FLAPS WERE INSPECTED FOR OBVIOUS DEFECTS, ALONG WITH THE TORQUE TUBES AND TRANSFER GEARBOXES. THE FLAP POS XMITTERS WERE INSPECTED AND THE POS INDICATOR WAS REPLACED AS A PRECAUTION. NOV/FRI/02, MUCH LIKE THE PREVIOUS DAY, THE FLAPS WOULD NOT EXTEND WHEN THE FLAP HANDLE WAS MOVED TO POS 1 DURING THE APCH. THE FLAP HANDLE WAS CYCLED BACK TO 0 AND AGAIN TO 1, THIS TIME WITH NORMAL RESULTS. FLAPS 30 WAS SELECTED AND THE LNDG WAS UNEVENTFUL. ALTERNATE FLAPS EXTENSION WAS NOT USED AND NO EMER WAS DECLARED. AGAIN, THE TRAILING EDGE FLAPS SYSTEM WAS INSPECTED FOR ANY VISUAL BINDING OR DEFECTS. THE OVERHEAD P5 FLT CTL PANEL WAS REPLACED (FROM WHERE THE ALTERNATE FLAPS ARE OPERATED), ALONG WITH THE R FLAP POSITION XMITTER (THOUGH, AS STATED PREVIOUSLY, AN ERRONEOUS ASYMMETRY INDICATION IS NOT LIKELY TO BE THE CAUSE WITH THE INFO KNOWN). THE ALTERNATE FLAP DRIVE MOTOR WAS ALSO REPLACED AT THIS TIME FOR THE FOLLOWING REASON: IF THE CAUSE OF THIS PROB WAS INDEED ASYMMETRY INDICATION, THEN THE ALTERNATE FLAP EXTENSION METHOD SHOULD HAVE DRIVEN THE TRAILING EDGE FLAPS TO THE DESIRED SETTING IN ON THE EARLIER OCCASION, AND A WEAK MOTOR MAY HAVE BEEN THE CAUSE. DEC/SUN/02, DURING TAXI FOR TKOF, THE FLAPS WOULD NOT EXTEND. THE ACFT RETURNED TO THE GATE AND MECHANICS REPLACED THE TRAILING EDGE FLAP POS INDICATOR (THE SECOND IN FOUR DAYS). AN OPERATIONAL CHECK WAS PERFORMED AND THE FLAPS WORKED NORMALLY. FLT APCH PHASE AGAIN, FLAP EXTENSION FAILED IN NORMAL. ALTERNATE PROCS WERE USED AND THE LNDG WAS UNEVENTFUL WITH NO EMER DECLARED. AFTER ANOTHER VISUAL INSPECTION OF THE FLAP SYSTEM, ALL JACKSCREW RESERVOIRS WERE SERVICED WITH NO RPTS OF DRY OR LOW LEVELS. THE FLAP CTL CABLE TENSIONS AND TENSION LOSS SWITCH WERE CHECKED, ALONG WITH THE FLAP BYPASS SHUTOFF VALVE (WHICH SUPPLIES OR REMOVES HYDRAULIC POWER FROM THE FLAP DRIVE MOTOR IN ALTERNATE OPERATION OR ASYMMETRIC CONDITIONS). THE FLAP/SLAT INDICATION MODULE WAS REPLACED AS A PRECAUTION (THIS UNIT WAS RTS'D YESTERDAY SINCE IT IS NOT A PART OF THE TRAILING EDGE FLAP ASYMMETRY PROTECTION). THE FLAPS WERE OPERATED EXTENSIVELY AND NO FURTHER DEFECTS WERE FOUND. DEC/MON/02, DURING APCH THE FLAPS WOULD NOT EXTEND NORMALLY. ALTERNATE FLAPS WERE USED AND LANDED SAFELY WITH FLAPS 15. AN EMER WAS NOT DECLARED. FIELD TECH, WAS CALLED IN TO ASSIST WITH THE TROUBLESHOOTING EFFORTS IMMEDIATELY IDENTIFIED A CORRODED CONNECTOR FOR THE RIGHT FLAP POSITION XMITTER AS WELL AS ANOTHER AT A JUNCTION BOX IN THE WHEEL WELL. ASIDE FROM THE INITIAL WRITE-UP IN ON THUR, ALL OTHER FAILURES WERE OVERRIDDEN WITH USE OF ALTERNATE FLAPS. AT THIS POINT, WITH THE POSSIBILITY THAT THE FLT CREW MAY HAVE MADE AN ERROR IN THE USE OF THE ALTERNATE FLAPS PROC, AND WITH THIS NEW FINDING, THE FOCUS WAS AGAIN SHIFTED TO THE INDICATION SYSTEM AND A SUBSEQUENT ERRONEOUS ASYMMETRY LOCKOUT CONDITION. THE TWO CONNECTORS WERE REPLACED AND THE SYSTEM OPERATIONALLY CHECKED SATISFACTORILY. DUE TO THE HISTORY OVER THE HOLIDAY WEEKEND, HOWEVER, WAS REQUESTED TO ALSO CHECK THE FLUID LEVELS OF ALL EIGHT FLAP XMISSIONS AND JACKSCREWS. THE #5 AND #6 XMISSIONS WERE FOUND TO BE UNDER SERVICED, BUT WITH NO EVIDENCE OF PAST OR PRESENT LEAKAGE. THEY WERE SERVICED TO THE PROPER LEVEL AND THE FLAPS WERE CHECKED ONE LAST TIME WITH NO DEFECTS. ONLY ONE FLT WAS MADEBEFORE THE FLAPS FAILED TO EXTEND, YET AGAIN, ON APCH TO ALTERNATE FLAPS WERE AGAIN USED TO EXTEND THE FLAPS TO 15 AND LNDG WAS UNEVENTFUL WITH NO EMER DECLARED. FIELD TECH, WAS ALSO CALLED IN TO ASSIST WITH THE TROUBLESHOOTING EFFORTS. #5 AND #6 FLAP XMISSIONS WERE AGAIN CHECKED AND #5 WAS FOUND TO BE LOW, IN FACT, AT ONLY 1/3 FULL. THE #4 AND #5 FLAP XMISSIONS WERE REPLACED AND THE FLAP SYSTEM WAS INSPECTED AND OPERATIONALLY CHECKED AGAIN, WITH NO DEFECTS FOUND. A FUNCTIONAL CHECK FLT WAS ARRANGED AND PERFORMED WITH SEVERAL APCHES AND FLAP CYCLES. THE ACFT WAS RETURNED TO SVC THIS AFTERNOON AND HAS OPERATED ONE REVENUE FLT WITH NO FURTHER PROBS RPTED.

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.