A B757-200 FLC EXPERIENCES A TRAILING EDGE FLAP DISAGREEMENT WARNING. AFTER A GAR AND CHKLIST USE; THE CREW (WHEN ON THE GND) FINDS THAT THEY USED A 30 DEG FLAP SETTING FOR LNDG VERSUS THE 20 DEG FLAP SETTING AS REQUIRED BY THE CHKLIST. SNA. CA.

Narrative

ON FINAL APCH WHEN SELECTING FLAP SETTINGS; EXPERIENCED A FLAP PROB (FLAP DISAGREEMENT WARNING). MADE GAR AND COMPLETED FLAP DISAGREEMENT ABNORMAL PROC. APCH AND NEXT LNDG NORMAL. UPON REVIEW; ONCE ON THE GND; WE DISCOVERED THAT WE MISREAD THE ABNORMAL PROC AND LANDED WITH WRONG FLAP SETTING. THE REASON WE MISREAD THE PROC WAS DUE TO RUSHING THE PROC BECAUSE OF LOW FUEL RESERVES AND LEVEL 4 TSTMS AT NIGHT; IN TURB; WITH HVY RAIN AND LIGHTNING; HVY WORKLOAD WITH ATC WHICH WAS SATURATED WITH ACFT; AND THE STRONG URGE TO GET THE ACFT ON THE GND BEFORE THE WX GOT WORSE. NEXT TIME I'LL TAKE MORE TIME AND MORE FUEL. SUPPLEMENTAL INFO FROM ACN 465170: DURING FINAL APCH PHASE OF FLT; 'TRAILING EDGE FLAP DISAGREEMENT' EICAS MESSAGE PRESENTED AT APPROX 2500 FT AGL. MISSED APCH WAS EXECUTED WITH SUBSEQUENT VECTORING AND REF TO ABNORMAL CHKLIST PROCS. ALTERNATE FLAP SYS WAS SELECTED. WHILE HOLDING FOR CLRNC TO GATE; CHKLIST FOR FLAP PROC WAS REVIEWED AND DISCOVERED TO HAVE BEEN MISREAD. THE PROPER PROC WAS TO LAND WITH FLAPS 20 DEGS; NOT 30 DEGS AS WE HAD. THIS IS TO PROVIDE A BETTER MISSED APCH ENVELOPE IN THE EVENT OF AN ENG FAILURE AND GAR ON SHORT FINAL. THE POORLY WRITTEN CHKLIST; WITH REF TO FLAPS 20 DEG LNDG BURIED IN THE CONTEXT OF THE ABNORMAL PROC; CAUSED BOTH PLTS TO MISS FLAPS 20 DEG REF. CORRECTIVE ACTION WOULD BE TO REWRITE ABNORMAL FLAP PROC IN A MORE BOLD FACE FORMAT; AS WELL AS CAREFUL AND DILIGENT REF TO ABNORMAL PROCS.