AN IMPROPERLY DEACTIVATED LIFT DUMPER ON A FOKKER 100 CAUSES A TKOF WARNING THAT IS IGNORED BY THE CREW; WHO COMPLETED THE TKOF ONLY TO FIND DURING A REVIEW INFLT; THAT THE PLACARD ISSUED BY MAINT WAS INCORRECT FOR THE ACTUAL PROB.

Narrative

DELAYED DEP FROM CYYZ. INFORMED DELAY WAS CANCELLED UPON GATE ARR. HURRYING TO GET STATION OUT TIME AND PAX TO ORD. ACFT WAS ON PLACARD FOR LIFT DUMPER UNSAFE MESSAGE. REVIEWED LOG AND MEL AND MPM FOR PROPER MAINT ACTION BASED ON THE ORIGINAL WRITE UP;'U-LIFT DUMPER UNSAFE' MESSAGE. AT DEP END OF RWY DURING TKOF; WARNING TEST TKOF WARNING SOUNDED; AND LIFT DUMPER UNSAFE MESSAGE DISPLAYED MFDU. SINCE ALL MAINT PROCS CHKED AND COMPLIED WITH; ASSUMED THIS CONDITION WAS NORMAL. TOOK OFF WITH TKOF WARNING AND LIFT DUMPER UNSAFE HORN ACTIVE. DETAILED REVIEW OF MEL; AFTER AIRBORNE; REVEALED MAINT PLACARDED ACFT IN ACCORDANCE WITH LIFT DUMPER FAULT MESSAGE 27-09B; INSTEAD OF LIFT DUMPER UNSAFE MESSAGE 27-09C. SHOULD NOT HAVE CONTINUED TKOF WITH TKOF WARNING HORN ON. LIFT DUMPER SYS WAS DEACTIVATED; SWITCH TURNED OFF; AND LNDG DISTANCE CORRECTIONS APPLIED FOR THE LNDG AT ORD. DUMPERS DID NOT DEPLOY. HAD MAINT MEET ACFT. COMPLETE DUMPER SYS DEACTIVATION REQUIRED AS PER MEL 27-09A. ORD SAID CYYZ MAINT SHOULD HAVE DISCONNECTED A COUPLE OF WARNING SYS CANNON PLUGS; BUT DID NOT. OTHERWISE; MAINT ACTION WAS CORRECT FOR ACTUAL PROB -- ACCORDING TO ORD MECHS. LESSONS: 1) DON'T TAKE OFF WITH TKOF WARNING HORN ON. 2) CHK THAT MEL CITATION IN MAINT BLOCK OF LOG MATCHES ORIGINAL DESCRIPTION OF PROB IN WRITE-UP. 3) DON'T TAKE OFF WITH TKOF WARNING HORN ON.