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.