A B737-700 INCURRED DAMAGE WHEN LEADING EDGE DEVICES WERE EXTENDED ON #1 ENG INBOARD CORE COWL OPEN FOR BORESCOPE INSPECTION.

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THE ASSIGNMENT FOR ACFT INCLUDED THE FOLLOWING TASKS: MAINT SVC; BIRD STRIKE BORESCOPE INSPECTION; FMC SOFTWARE UPLOADS; CABLE TENSION CHK OF THE LNDG GEAR CTL CABLE; A C-CHK CARRYOVER FOR THE #1 LEADING EDGE FLAP ICE SEAL; AND SEVERAL CABIN C-CHK CARRYOVER ITEMS. ANOTHER TECHNICIAN AND I WERE IN THE PROCESS OF COOLING THE #1 ENG FOR THE BIRD STRIKE BORESCOPE INSPECTION; WHILE ADDRESSING SOME OF THE OTHER WORK PACKAGE ITEMS. WE OPENED THE E1 OUTBOARD FAN AND CORE COWLS ONLY; FOR ENG COOLING PURPOSES. WE DISCUSSED THE NEED TO FULLY DEPLOY THE FLAPS FOR THE EXTERIOR PORTION OF THE MAINT WALK-AROUND INSPECTION AND REPLACEMENT OF THE #1 LEADING EDGE FLAP ICE-SEAL. I WAS TO CONTINUE THE EXTERIOR WALK-AROUND PORTION OF THE MAINT SVC; WHILE OTHER TECHNICIANS WERE LOADING SOFTWARE IN THE FMC'S. ACFT: I WAS LOWERING THE FLAPS; WHILE AT THE TIME; UNAWARE THAT THE #4 LEADING EDGE SLAT WOULD CONTACT THE OPENED OUTBOARD CORE COWL. THE #4 SLAT IMPACTED THE OUTBOARD CORE COWL AT THE SLAT FULL EXIT POS. I HEARD THE IMPACT AND IMMEDIATELY TURNED THE 'B' HYD SYS EMDP OFF. I INSPECTED THE DAMAGE AND NOTIFIED MY SUPVR. THE ACFT DID NOT FLY UNDER THIS CONDITION. WE TOWED THE ACFT TO THE HANGAR. THE E1 OUTBOARD THRUST REVERSER SLEEVE WAS REMOVED AND REPLACED PRIOR TO THE ACFT RETURNING TO SVC. SUPPLEMENTAL 591075: BOTH MECHS SHOULD HAVE FOLLOWED MAINT MANUAL AND ACR PROCS ON DEPLOYMENT OF FLAPS WITH CORE COWLS OPEN -- PERCEPTIONS -- MECH #2 THOUGHT MECH # 1 WAS ONLY GOING TO BRING FLAP DOWN TO 1 UNIT TO CHANGE ICE SEAL ON #1 KRUGGER FLAP.