Narrative:

In final stages of 3 plus hour flight received series of descents from approach. During descent to 9;000 MSL; approach directed a speed of 210 KIAS; then continued descent from 9;000 to 8;000. During slowdown; I directed the first officer to select flaps 1 and all le and te devices deployed normally. Calling for flaps 5 resulted in flap indications stopping at about 2. No change in flight characteristics were noted confirming flap indications. Abnormal checklist for te flap disagree was initiated. As per the checklist; attempt to extend flaps via alternate flap motor to flaps 15 was unsuccessful as flap indications stayed symmetrical but no more than about 4.7 degrees. Emergency was declared with approach and landing/rollout otherwise uneventful. After deplaning passengers; maintenance began troubleshooting and all te and le flaps/slats operated normally. Alternate flap motor also operated the flaps normally. Maintenance and I suspected ice as being a potential factor; especially considering the additional air loads on the te flaps during extension in flight. During troubleshooting; maintenance reported to me that they had discovered 4 over torque indicators had popped in the locations that would indicate an over torque situation had been present in flight. As a precaution; they were going to take the aircraft out of service to the hangar for further troubleshooting. Airport temperature was plus 1 centigrade on landing. Inflight temperatures: FL290 initial altitude for ride (approximately 1 hour duration): sat -43 to -47 in cloud with subsequent climb to 370 much colder. Icing conditions during climbout requiring use of engine anti ice but no cockpit indications of airframe icing. Wing anti-ice not used at any time during flight. Just by chance; my next arrival into this airport was the next evening. Also by chance; one of the lead mechanics that had worked on the flap problem the night before was at the gate for a normal logbook check. We discussed the malfunction from the previous night and he informed me that they had pulled the aircraft into the hangar and had found water in the drive mechanism (dumb pilot note: not sure where since I'm a pilot and I can't remember exactly where he told me it occurred) but in my mind positively confirming the diagnosis of ice. He also mentioned that the buildup of water should be cleared on normal periodic maintenance checks which apparently had not happened. If our assumptions are correct; more diligent normal maintenance practices would most likely have precluded this event. My experience with my airline is that the maintenance is normally excellent; but complacency and/or time constraints can and do occur. Including incidents such as these into a periodic 'awareness' program may just be the incentive for the individual to do the check properly.

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Original NASA ASRS Text

Title: A B737 trailing edge flap drive motor had accumulated moisture which froze in flight and caused a flap asymmetry as the flaps were extended beyond flaps 1.

Narrative: In final stages of 3 plus hour flight received series of descents from Approach. During descent to 9;000 MSL; Approach directed a speed of 210 KIAS; then continued descent from 9;000 to 8;000. During slowdown; I directed the First Officer to select flaps 1 and all LE and TE devices deployed normally. Calling for flaps 5 resulted in flap indications stopping at about 2. No change in flight characteristics were noted confirming flap indications. Abnormal checklist for TE flap disagree was initiated. As per the checklist; attempt to extend flaps via alternate flap motor to flaps 15 was unsuccessful as flap indications stayed symmetrical but no more than about 4.7 degrees. Emergency was declared with Approach and landing/rollout otherwise uneventful. After deplaning passengers; Maintenance began troubleshooting and all TE and LE flaps/slats operated normally. Alternate flap motor also operated the flaps normally. Maintenance and I suspected ice as being a potential factor; especially considering the additional air loads on the TE flaps during extension in flight. During troubleshooting; Maintenance reported to me that they had discovered 4 over torque indicators had popped in the locations that would indicate an over torque situation had been present in flight. As a precaution; they were going to take the aircraft out of service to the hangar for further troubleshooting. Airport temperature was plus 1 centigrade on landing. Inflight temperatures: FL290 initial altitude for ride (approximately 1 hour duration): SAT -43 to -47 in cloud with subsequent climb to 370 much colder. Icing conditions during climbout requiring use of Engine Anti Ice but no cockpit indications of airframe icing. Wing anti-ice not used at any time during flight. Just by chance; my next arrival into this airport was the next evening. Also by chance; one of the lead mechanics that had worked on the flap problem the night before was at the gate for a normal logbook check. We discussed the malfunction from the previous night and he informed me that they had pulled the aircraft into the hangar and had found water in the drive mechanism (dumb pilot note: not sure where since I'm a pilot and I can't remember exactly where he told me it occurred) but in my mind positively confirming the diagnosis of ice. He also mentioned that the buildup of water should be cleared on normal periodic maintenance checks which apparently had not happened. If our assumptions are correct; more diligent normal maintenance practices would most likely have precluded this event. My experience with my airline is that the maintenance is normally excellent; but complacency and/or time constraints can and do occur. Including incidents such as these into a periodic 'awareness' program may just be the incentive for the individual to do the check properly.

Data retrieved from NASA's ASRS site as of April 2012 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.