A B737 captain reported a 'pop' sound accompanied with a left roll as flaps 25 were selected for lan...

Narrative:

Configuring to land flaps 30. When flaps 25 was selected; both pilots heard a pop and the aircraft began to roll left. Opposite aileron by the first officer (pilot flying) countered the roll. Captain stated flaps were being returned to 15 degrees and then selected flaps 15. Roll inclination improved; but was still present. V-speeds for flaps 15 landing were set and landing was made without incident and minimal braking. Passengers were never aware of any problems. Made write-up in logbook and called maintenance control as well as local maintenance. Waited for inbound crew and relayed experience to them. I have never experienced this in my career. I have no idea what happened and only associate it as a flap abnormality because the pop occurred while flaps were being selected.

Original NASA ASRS Text

Title: A B737 Captain reported a 'pop' sound accompanied with a left roll as flaps 25 were selected for landing. The flaps were selected to 15; the V speed reset; and the landing completed with aileron input required.

Narrative: Configuring to land flaps 30. When flaps 25 was selected; both pilots heard a pop and the aircraft began to roll left. Opposite aileron by the First Officer (pilot flying) countered the roll. Captain stated flaps were being returned to 15 degrees and then selected flaps 15. Roll inclination improved; but was still present. V-speeds for flaps 15 landing were set and landing was made without incident and minimal braking. Passengers were never aware of any problems. Made write-up in logbook and called Maintenance Control as well as Local Maintenance. Waited for inbound crew and relayed experience to them. I have never experienced this in my career. I have no idea what happened and only associate it as a flap abnormality because the pop occurred while flaps were being selected.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	996752
Time
Date	201202
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Component
Aircraft Component	Trailing Edge Flap
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical

A B737 captain reported a 'pop' sound accompanied with a left roll as flaps 25 were selected for landing. The flaps were selected to 15; the V speed reset; and the landing completed with aileron input required.