Narrative:

The captain and I started our day 4 of a 4-DAY trip. We configured for off gate deicing; engines shut down and flaps set at 5 degrees for takeoff. The flaps were up when we arrived at the aircraft and indicated up; both inside on the gauge and externally; on walkaround. Deicing and flight to city was uneventful; my first officer leg. On next flight (captain's leg); upon leveloff; yoke was tilted to the right of center and the captain put in 1 1/2-2 units of right rudder to center yoke; not overly unusual. Power and fuel was in balance and all flap/slat indications normal. Centered rudder trim on approach and uneventful landing. Last leg of the trip (first officer leg out). Off the gate 2 mins late (blocked pushback from other aircraft); and blocked in 1 min late (WX holding going into our destination city). Takeoff flaps 5 degrees; uneventful. After final flap retraction; the aircraft wanted to roll to the left. I was hand flying the aircraft. We continued our climb to altitude; hand flying all the way up and I trimmed the aircraft before autoplt engagement. Again we needed 2 units right rudder to keep yoke centered. Power and fuel in balance and all flap/slat indications normal; full up. Upon confign for landing I noticed that I could center the rudder trim and the aircraft and yoke tracked straight. Uneventful flaps 40 degrees landing (RVR 5000 ft) in destination and maintenance was called to take a look at our rigging problem. We suspected rigging; because of no other indications; and we had not oversped the flaps at any time. Oncoming pm first officer noticed right inboard flap extended about 10 degrees with flaps up; during his walkaround. All other flaps up. The captain and I went outside with maintenance and we were told what was causing the problem. A metal roundstock rod that pulls the inboard flaps up had pulled out from its anchor point; for the right inboard flap. The rod was resting in the flap track and canoe; as it was only attached to the flap and not its forward anchor point (2 bolts). We believe that we followed all guidelines and don't know if this could have been prevented. We don't know if the inbound crew the night before had put the flaps all the way up or to flaps 15 degrees; during the snowstorm. We were not present for the first deicing and never had any indications of a flap hanging problem. We suspected rigging on the flight from ZZZ1 because of no roll control problems on the 2 previous flts. In hindsight; I would have gone outside in ZZZ1 since the captain had used up to 2 units of rudder trim on his leg; and looked at the flaps and entire wing area. Maintenance said sometimes ice; water; and snow can get in those flap tracks and then freeze; causing problems later? We all know this and that is why we have the flaps 15 degree procedure; with clutter present; but was this the cause? We don't know. We referenced the QRH during climb out of ZZZ1 and found nothing that applied to our problem. After speaking with maintenance control; it was the right flap retract rod (linkage rod) that pulls up the aft flap section. The fore flap section is where the flap gauge gets its input from; therefore we had no indication in the cockpit. They said this has happened in the past and will happen again and there is no procedure for it in our QRH. Maintenance control told me we did not overspeed that section (aft) of the right inboard flap in that situation and they do not consider that an overspeed. If we are not required to do a walkaround after each flight; then maybe the ground crew can take a quick look and let us know if anything is unusual. I know they normally will do this and they have found many problems in the past; but they might require a little extra training; on their part. I should have gone out and looked externally for myself as we needed zero rudder trim on the first leg and 2 units on the second leg; even though no roll was noticed. The rod may have broken at altitude on the second leg and was never noticed; because we configured for the second approach into ZZZ1 with the autoplt on. Do we need to address this; from a crew procedure; when this happens again? There is no procedure that we know of. We have no indicators in the cockpit; for this particular problem. Supplemental information from acn 728705: itis not unusual to fly an older B737 (this one is approximately 6 yrs old) and require 2 units of rudder trim. My suspicion is that the flaps were not inspected before being fully retracted the previous evening with ice and snow present. 2 things: I will now make a serious note of the actual trim position on acceptance of an aircraft for a useful reference point for any flight control problems. Second; if there is any future roll or yaw questions of any sort; I will first perform a walkaround or call maintenance. Since the cockpit indications were all normal; I would also like the company to seriously consider any checklist additions or procedures to help identify these problems. Callback conversation with reporter revealed the following information: reporter stated that maintenance had found the inboard aft flap extend/retract control rod was bent to the point of breaking. This same rod was not disconnected nor separated from the flap; but bent in the middle. This contributed to the need for rudder trim.

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Original NASA ASRS Text

Title: A B737-700 ACFT HAD SUSPECTED FLT CONTROL RIGGING PROBS DUE TO ACFT REQUIRED 1.5 TO 2 UNITS OF R RUDDER TRIM WHEN NOT IN CRUISE.

Narrative: THE CAPT AND I STARTED OUR DAY 4 OF A 4-DAY TRIP. WE CONFIGURED FOR OFF GATE DEICING; ENGS SHUT DOWN AND FLAPS SET AT 5 DEGS FOR TKOF. THE FLAPS WERE UP WHEN WE ARRIVED AT THE ACFT AND INDICATED UP; BOTH INSIDE ON THE GAUGE AND EXTERNALLY; ON WALKAROUND. DEICING AND FLT TO CITY WAS UNEVENTFUL; MY FO LEG. ON NEXT FLT (CAPT'S LEG); UPON LEVELOFF; YOKE WAS TILTED TO THE R OF CTR AND THE CAPT PUT IN 1 1/2-2 UNITS OF R RUDDER TO CTR YOKE; NOT OVERLY UNUSUAL. PWR AND FUEL WAS IN BAL AND ALL FLAP/SLAT INDICATIONS NORMAL. CTRED RUDDER TRIM ON APCH AND UNEVENTFUL LNDG. LAST LEG OF THE TRIP (FO LEG OUT). OFF THE GATE 2 MINS LATE (BLOCKED PUSHBACK FROM OTHER ACFT); AND BLOCKED IN 1 MIN LATE (WX HOLDING GOING INTO OUR DEST CITY). TKOF FLAPS 5 DEGS; UNEVENTFUL. AFTER FINAL FLAP RETRACTION; THE ACFT WANTED TO ROLL TO THE L. I WAS HAND FLYING THE ACFT. WE CONTINUED OUR CLB TO ALT; HAND FLYING ALL THE WAY UP AND I TRIMMED THE ACFT BEFORE AUTOPLT ENGAGEMENT. AGAIN WE NEEDED 2 UNITS R RUDDER TO KEEP YOKE CTRED. PWR AND FUEL IN BAL AND ALL FLAP/SLAT INDICATIONS NORMAL; FULL UP. UPON CONFIGN FOR LNDG I NOTICED THAT I COULD CTR THE RUDDER TRIM AND THE ACFT AND YOKE TRACKED STRAIGHT. UNEVENTFUL FLAPS 40 DEGS LNDG (RVR 5000 FT) IN DEST AND MAINT WAS CALLED TO TAKE A LOOK AT OUR RIGGING PROB. WE SUSPECTED RIGGING; BECAUSE OF NO OTHER INDICATIONS; AND WE HAD NOT OVERSPED THE FLAPS AT ANY TIME. ONCOMING PM FO NOTICED R INBOARD FLAP EXTENDED ABOUT 10 DEGS WITH FLAPS UP; DURING HIS WALKAROUND. ALL OTHER FLAPS UP. THE CAPT AND I WENT OUTSIDE WITH MAINT AND WE WERE TOLD WHAT WAS CAUSING THE PROB. A METAL ROUNDSTOCK ROD THAT PULLS THE INBOARD FLAPS UP HAD PULLED OUT FROM ITS ANCHOR POINT; FOR THE R INBOARD FLAP. THE ROD WAS RESTING IN THE FLAP TRACK AND CANOE; AS IT WAS ONLY ATTACHED TO THE FLAP AND NOT ITS FORWARD ANCHOR POINT (2 BOLTS). WE BELIEVE THAT WE FOLLOWED ALL GUIDELINES AND DON'T KNOW IF THIS COULD HAVE BEEN PREVENTED. WE DON'T KNOW IF THE INBOUND CREW THE NIGHT BEFORE HAD PUT THE FLAPS ALL THE WAY UP OR TO FLAPS 15 DEGS; DURING THE SNOWSTORM. WE WERE NOT PRESENT FOR THE FIRST DEICING AND NEVER HAD ANY INDICATIONS OF A FLAP HANGING PROB. WE SUSPECTED RIGGING ON THE FLT FROM ZZZ1 BECAUSE OF NO ROLL CTL PROBS ON THE 2 PREVIOUS FLTS. IN HINDSIGHT; I WOULD HAVE GONE OUTSIDE IN ZZZ1 SINCE THE CAPT HAD USED UP TO 2 UNITS OF RUDDER TRIM ON HIS LEG; AND LOOKED AT THE FLAPS AND ENTIRE WING AREA. MAINT SAID SOMETIMES ICE; WATER; AND SNOW CAN GET IN THOSE FLAP TRACKS AND THEN FREEZE; CAUSING PROBS LATER? WE ALL KNOW THIS AND THAT IS WHY WE HAVE THE FLAPS 15 DEG PROC; WITH CLUTTER PRESENT; BUT WAS THIS THE CAUSE? WE DON'T KNOW. WE REFED THE QRH DURING CLBOUT OF ZZZ1 AND FOUND NOTHING THAT APPLIED TO OUR PROB. AFTER SPEAKING WITH MAINT CTL; IT WAS THE R FLAP RETRACT ROD (LINKAGE ROD) THAT PULLS UP THE AFT FLAP SECTION. THE FORE FLAP SECTION IS WHERE THE FLAP GAUGE GETS ITS INPUT FROM; THEREFORE WE HAD NO INDICATION IN THE COCKPIT. THEY SAID THIS HAS HAPPENED IN THE PAST AND WILL HAPPEN AGAIN AND THERE IS NO PROC FOR IT IN OUR QRH. MAINT CTL TOLD ME WE DID NOT OVERSPEED THAT SECTION (AFT) OF THE R INBOARD FLAP IN THAT SITUATION AND THEY DO NOT CONSIDER THAT AN OVERSPEED. IF WE ARE NOT REQUIRED TO DO A WALKAROUND AFTER EACH FLT; THEN MAYBE THE GND CREW CAN TAKE A QUICK LOOK AND LET US KNOW IF ANYTHING IS UNUSUAL. I KNOW THEY NORMALLY WILL DO THIS AND THEY HAVE FOUND MANY PROBS IN THE PAST; BUT THEY MIGHT REQUIRE A LITTLE EXTRA TRAINING; ON THEIR PART. I SHOULD HAVE GONE OUT AND LOOKED EXTERNALLY FOR MYSELF AS WE NEEDED ZERO RUDDER TRIM ON THE FIRST LEG AND 2 UNITS ON THE SECOND LEG; EVEN THOUGH NO ROLL WAS NOTICED. THE ROD MAY HAVE BROKEN AT ALT ON THE SECOND LEG AND WAS NEVER NOTICED; BECAUSE WE CONFIGURED FOR THE SECOND APCH INTO ZZZ1 WITH THE AUTOPLT ON. DO WE NEED TO ADDRESS THIS; FROM A CREW PROC; WHEN THIS HAPPENS AGAIN? THERE IS NO PROC THAT WE KNOW OF. WE HAVE NO INDICATORS IN THE COCKPIT; FOR THIS PARTICULAR PROB. SUPPLEMENTAL INFO FROM ACN 728705: ITIS NOT UNUSUAL TO FLY AN OLDER B737 (THIS ONE IS APPROX 6 YRS OLD) AND REQUIRE 2 UNITS OF RUDDER TRIM. MY SUSPICION IS THAT THE FLAPS WERE NOT INSPECTED BEFORE BEING FULLY RETRACTED THE PREVIOUS EVENING WITH ICE AND SNOW PRESENT. 2 THINGS: I WILL NOW MAKE A SERIOUS NOTE OF THE ACTUAL TRIM POS ON ACCEPTANCE OF AN ACFT FOR A USEFUL REF POINT FOR ANY FLT CTL PROBS. SECOND; IF THERE IS ANY FUTURE ROLL OR YAW QUESTIONS OF ANY SORT; I WILL FIRST PERFORM A WALKAROUND OR CALL MAINT. SINCE THE COCKPIT INDICATIONS WERE ALL NORMAL; I WOULD ALSO LIKE THE COMPANY TO SERIOUSLY CONSIDER ANY CHKLIST ADDITIONS OR PROCS TO HELP IDENT THESE PROBS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT MAINT HAD FOUND THE INBOARD AFT FLAP EXTEND/RETRACT CONTROL ROD WAS BENT TO THE POINT OF BREAKING. THIS SAME ROD WAS NOT DISCONNECTED NOR SEPARATED FROM THE FLAP; BUT BENT IN THE MIDDLE. THIS CONTRIBUTED TO THE NEED FOR RUDDER TRIM.

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.