Narrative:

During the descent to ZZZ; the #4 leading edge flap in transit amber light on the overhead panel illuminated with an associated amber 'leading edge flaps transit' light on the forward panel. We began to slow the aircraft to 230 KTS and the light went out somewhere prior to 250 KTS. The captain wrote up the anomaly in ACARS. When on approach to ZZZ approach control slowed us to 170 KTS. We selected flaps 10 degrees. As the flaps passed through 5 degrees; the amber 'leading edge flaps transit' stayed illuminated. We looked at the leading edge flaps annunciator panel on the overhead and saw that all leading edge devices were fully retracted when they should have been in the 'full extend' position. We sped up; retracted the flaps and recycled them with the same result. We had approach vector us off the arrival and we consulted the flight manual. We found no irregular checklist for 'leading edge flaps not extended.' the captain called maintenance control. Maintenance control advised the captain to recycle a couple of breakers on the P6-2 panel. (I was flying the aircraft and didn't hear or see which ones.) we recycled the flaps again with no change in the situation. We consulted the flight manual and found the proper speed for landing with no leading edge devices (reference 15 + 5 KTS). We set up for another approach and landing. Everything on the approach was normal except for the slightly higher reference speed. Somewhere on the approach; the leading edge flap indictor on the overhead indicated that all the leading edge devices were 'in transit;' but they never moved to the extended position; rather they appeared to be about 1/2 way extended. We made a normal landing and made the turnoff with no excessive braking or reverse thrust. After landing; we elected to retract the flaps. The leading edge devices would not retract; they stayed in the same half-extended position as they were on final approach.

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Original NASA ASRS Text

Title: B737-500 EXPERIENCES FAILURE OF LEADING EDGE DEVICES TO FULLY EXTEND.

Narrative: DURING THE DSCNT TO ZZZ; THE #4 LEADING EDGE FLAP IN TRANSIT AMBER LIGHT ON THE OVERHEAD PANEL ILLUMINATED WITH AN ASSOCIATED AMBER 'LEADING EDGE FLAPS TRANSIT' LIGHT ON THE FORWARD PANEL. WE BEGAN TO SLOW THE ACFT TO 230 KTS AND THE LIGHT WENT OUT SOMEWHERE PRIOR TO 250 KTS. THE CAPT WROTE UP THE ANOMALY IN ACARS. WHEN ON APCH TO ZZZ APCH CTL SLOWED US TO 170 KTS. WE SELECTED FLAPS 10 DEGS. AS THE FLAPS PASSED THROUGH 5 DEGS; THE AMBER 'LEADING EDGE FLAPS TRANSIT' STAYED ILLUMINATED. WE LOOKED AT THE LEADING EDGE FLAPS ANNUNCIATOR PANEL ON THE OVERHEAD AND SAW THAT ALL LEADING EDGE DEVICES WERE FULLY RETRACTED WHEN THEY SHOULD HAVE BEEN IN THE 'FULL EXTEND' POS. WE SPED UP; RETRACTED THE FLAPS AND RECYCLED THEM WITH THE SAME RESULT. WE HAD APCH VECTOR US OFF THE ARR AND WE CONSULTED THE FLT MANUAL. WE FOUND NO IRREGULAR CHKLIST FOR 'LEADING EDGE FLAPS NOT EXTENDED.' THE CAPT CALLED MAINT CTL. MAINT CTL ADVISED THE CAPT TO RECYCLE A COUPLE OF BREAKERS ON THE P6-2 PANEL. (I WAS FLYING THE ACFT AND DIDN'T HEAR OR SEE WHICH ONES.) WE RECYCLED THE FLAPS AGAIN WITH NO CHANGE IN THE SITUATION. WE CONSULTED THE FLT MANUAL AND FOUND THE PROPER SPD FOR LNDG WITH NO LEADING EDGE DEVICES (REF 15 + 5 KTS). WE SET UP FOR ANOTHER APCH AND LNDG. EVERYTHING ON THE APCH WAS NORMAL EXCEPT FOR THE SLIGHTLY HIGHER REF SPD. SOMEWHERE ON THE APCH; THE LEADING EDGE FLAP INDICTOR ON THE OVERHEAD INDICATED THAT ALL THE LEADING EDGE DEVICES WERE 'IN TRANSIT;' BUT THEY NEVER MOVED TO THE EXTENDED POS; RATHER THEY APPEARED TO BE ABOUT 1/2 WAY EXTENDED. WE MADE A NORMAL LNDG AND MADE THE TURNOFF WITH NO EXCESSIVE BRAKING OR REVERSE THRUST. AFTER LNDG; WE ELECTED TO RETRACT THE FLAPS. THE LEADING EDGE DEVICES WOULD NOT RETRACT; THEY STAYED IN THE SAME HALF-EXTENDED POS AS THEY WERE ON FINAL APCH.

Data retrieved from NASA's ASRS site as of May 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.