Narrative:

On approach; EICAS messages le slat disagree and te flap asym posted after selection of flaps 25. Captain then moved the flap selector back to flaps 20. We initiated a go-around and received ATC instructions to continue track and maintain 2;000 ft. I asked for gear up. The captain elected to leave the gear in the down position because he was not sure if the gear horn would sound. The flap needles appeared to be aligned and in the white band at 20 degrees; but the needles appeared just beyond the center mark in the middle of the band. I agreed that we could leave the gear down if he wanted and noted the fuel remaining at 15;000 pounds. The captain then told me to continue flying the airplane and take over ATC communications and he would run through the QRH procedures and talk to the passengers and crew. I received a few ATC instructions while the captain began the first QRH checklist. Le slat disagree was posted at the top of the EICAS; so we started with this procedure. At some point he told me he was going to go to the other procedure; te flap asym; as it indicated to do so. I tried to pay attention to the QRH procedures as he read them aloud as much as I could; but I may have missed some information as I was receiving ATC instructions for a heading; altitude; and frequency changes. I confirmed these changes with the captain as I received them. I heard him read items from the checklist and saw him perform the instruction. We asked ATC to keep us fairly close to the airport because we believed that the checklist shouldn't take very long and didn't want to stray to far away with the higher fuel burn. After he finished the te abnormal; the captain went back to the le asym procedure to compete it. After a few minutes we completed the checklist and he took over the communications as I continued to fly the aircraft. He then declared an emergency and we were given a new runway assignment. I briefed the approached and we landed with flaps 20. Some additional thoughts: during the first approach while on the downwind portion; we noted a heavy 777 that we would be following for [our original runway]. That traffic was cleared for [the runway] and after we called him in sight; we were cleared for [the runway]. During the base turn and descent (I think out of 4;000 ft) we encountered light to moderate turbulence. It could have been wake turbulence or some turbulence due to winds. While on downwind I noted the wind was from a northerly direction around 35-40 KTS. We were at 210 KTS with flaps 5 and after we were given the lower altitude and told to slow to 170 KTS; I asked for flaps 15. As we descended and turned to base; the wind changed very quickly to around 15 KTS. In doing so; the indicated airspeed quickly ran up to the flap limit and it's possible it may have momentarily bumped past the limit speed. I'm not sure if this was a factor in the flap abnormal; as we were still able to go from flaps 15 to 20; but thought I would mention it. After talking with the maintenance technicians; they said they didn't see any indications of overspeed.

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Original NASA ASRS Text

Title: A B757 EICAS alerted LE SLAT DISAGREE and TE FLAP ASYM after flaps 25 was selected on approach at about the same time as a light to moderate turbulence event. A go-around was executed; the QRH completed and an uneventful landing followed.

Narrative: On approach; EICAS messages LE Slat Disagree and TE Flap ASYM posted after selection of flaps 25. Captain then moved the flap selector back to flaps 20. We initiated a go-around and received ATC instructions to continue track and maintain 2;000 FT. I asked for gear up. The Captain elected to leave the gear in the down position because he was not sure if the gear horn would sound. The flap needles appeared to be aligned and in the white band at 20 degrees; but the needles appeared just beyond the center mark in the middle of the band. I agreed that we could leave the gear down if he wanted and noted the fuel remaining at 15;000 LBS. The Captain then told me to continue flying the airplane and take over ATC communications and he would run through the QRH procedures and talk to the passengers and crew. I received a few ATC instructions while the Captain began the first QRH checklist. LE Slat Disagree was posted at the top of the EICAS; so we started with this procedure. At some point he told me he was going to go to the other procedure; TE Flap ASYM; as it indicated to do so. I tried to pay attention to the QRH procedures as he read them aloud as much as I could; but I may have missed some information as I was receiving ATC instructions for a heading; altitude; and frequency changes. I confirmed these changes with the Captain as I received them. I heard him read items from the checklist and saw him perform the instruction. We asked ATC to keep us fairly close to the airport because we believed that the checklist shouldn't take very long and didn't want to stray to far away with the higher fuel burn. After he finished the TE Abnormal; the Captain went back to the LE ASYM procedure to compete it. After a few minutes we completed the checklist and he took over the communications as I continued to fly the aircraft. He then declared an emergency and we were given a new runway assignment. I briefed the approached and we landed with flaps 20. Some additional thoughts: During the first approach while on the downwind portion; we noted a heavy 777 that we would be following for [our original runway]. That traffic was cleared for [the runway] and after we called him in sight; we were cleared for [the runway]. During the base turn and descent (I think out of 4;000 FT) we encountered light to moderate turbulence. It could have been wake turbulence or some turbulence due to winds. While on downwind I noted the wind was from a northerly direction around 35-40 KTS. We were at 210 KTS with flaps 5 and after we were given the lower altitude and told to slow to 170 KTS; I asked for flaps 15. As we descended and turned to base; the wind changed very quickly to around 15 KTS. In doing so; the indicated airspeed quickly ran up to the flap limit and it's possible it may have momentarily bumped past the limit speed. I'm not sure if this was a factor in the flap abnormal; as we were still able to go from flaps 15 to 20; but thought I would mention it. After talking with the maintenance technicians; they said they didn't see any indications of overspeed.

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.