2011-03 · NASA ASRS report 938564
B737 flight crew discovers flap damage during post flight inspection after noting abnormal trim requirements during flight. The damage may have occurred earlier in the day after approach and landing in icing conditions; when the flaps were retracted after landing without being inspected.
We landed after an ILS approach. Weather was: 005BKN 3/4SM -SNBR temperature 01C. The braking action was reported good by Company aircraft approximately five minutes prior to our landing. There was light mixed icing on the arrival/approach. Upon exiting the runway; retracted flaps as normal and taxied to gate. There was some light; wet snow accumulation on the taxiway and ramp surfaces. A flaps 15 retraction after landing for flap inspection upon arrival was not considered; the conditions did not appear to warrant it. The focus was on a safe runway crossing and taxi in the reduced visibility conditions. When we pushed for the next leg we ended up with an approximately 90-minute delay for deicing. We configured for a flaps 5 departure just after pushback; as normal; and then joined the line for deice. When we finally deiced (Type I and IV); the engines were shut down. The Deice Crew was split between two trucks and said that they would remove some accumulation around our landing gear. The deice was routine other than the long delay. We departed and flew the next leg which was 4:10 block with a hold and a divert consideration due to thunderstorms. The next leg; while maneuvering around the weather on climbout; we noticed some unusual trim inputs were needed to coordinate the aircraft. The Captain (now the pilot flying) flew with both the autopilot on and off to evaluate the aircraft's handling. The autopilot appeared to handle the trim requirements when on; when off; the aircraft was somewhat awkward to coordinate with the trim. We had no cockpit indication of asymmetry due to either flight controls or engine thrust. We consulted the QRH and discussed any appropriate action that might be taken; and agreed that the aircraft was safe to fly; trimmed a little bit unusually; but we might investigate further upon arrival. Upon a normal arrival and visual approach; the post-flight inspection revealed a partially extended outer panel of the left wing inboard trailing edge flap. The flaps were selected up after landing as normal; and there had never been any cockpit indication of asymmetry other than the unusual trim.
Approach was uneventful. We landed and cleared the runway; at which point I called for 'flaps up.' It was actively snowing; but I did not believe the runway was cluttered. We gave a braking report to the Tower and Operations of 'fair' and at the gate sent an ACARS FCR stating 'FAIR; No clutter.'It continued to snow and; in fact; it got heavier and wetter. We had a normal turn and were then held on the gate for a deicing slot. As the snow increased to what I considered moderate I included the possibility of clutter into my planning. We ran the departure numbers for clutter and we were fine. Additionally; we briefed the passengers that we would be cycling the gear on departure to preclude the possibility of frozen contaminants adhering to the gear. When it did come time to deice; we did so with engines off (the normal procedure is to deice engines running) so that the underside of our wings and gear could be checked (the Deice Crew said they knocked off some slush from the gear). We finally departed 90 minutes after push. The next flight; which was blocked for 2:10 took 4:11 due to deicing and holding for weather over the field on arrival (we stayed busy with the possible divert). Otherwise the flight was normal.During the next flight; I noticed an odd trim condition. The aircraft did in fact trim but there was a small roll to the left. Again; I was able to trim this out. Just to be safe; the First Officer investigated. All indications were normal with flaps up and flaps down; no asymmetry; no unusual fuel usage; no strange noises and no word from the back. So; after an uneventful landing; I briefed the new Captain on the unusual trim. Then the new First Officer came back in from the walk around and asked if it was normal for the flaps to be hanging. I said no and went outside to check the flaps. The aft portion of the left inboard most trailing edge flap was hanging. The attach bracket (attaches the aft section to the forward section) had sheared. (Maintenance was there and said the flap gauge runs off the forward portion of that flap; so if the forward portion is retracted; and it was; then the gauge will show full up.)First; when I checked the field condition (ACARS); I was not triggered for clutter. The field report was wet/good; no clutter. Second; due to the conflicting braking action reports; I was very focused on a good approach and landing; and then stopping the aircraft. I did all that; and when I cleared the runway; I was still focused on 'cornering action' and I simply commanded 'flaps up. Third; my mental threshold for clutter was not reached. I was not landing in or taxiing in deep slush and gunk. I have reread the pertinent FOM section and it states 'If airframe icing is suspected during approach; after landing; and/or taxi through water or slush; do not retract the flaps beyond flaps 15....' This is a much bigger definition than my mental image of landing in significant slush.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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