AN LJ-25 PILOT REPORTS THAT A SPOILER WAS DAMAGED BY THE AIRFLOW WHEN IT WAS DEPLOYED IN FLIGHT.

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ON MAR/WED/07 I WAS PF AND PIC OF A LEAR 25 GOING TO MFE. DURING DSCNT THROUGH APPROX FL200; I EXTENDED THE SPOILERS. SPDS AND G FORCES WERE NORMAL. ABOUT 6 SECONDS LATER THERE WAS A PERCEPTIBLE CHANGE IN THE FLT CHARACTERISTICS AS IF SOMETHING HAD 'LET GO.' THE ACFT HAD A SLIGHT R ROLLING TENDENCY EQUIVALENT TO ABOUT FULL R ROLL TRIM DEFLECTION. I RETRACTED THE SPOILERS AND THE ACFT FLEW NORMALLY. I EXTENDED THEM AGAIN AND GOT THE SAME R ROLLING TENDENCY. THE FO AND I BRIEFED THAT WE WOULD DELAY SPOILER DEPLOYMENT ON LNDG TO ENSURE CTL THROUGHOUT THE ROLLOUT. A FEW MINS LATER ON ABOUT 2 MI FINAL; THE SPOILER DEPLOYED LIGHT ILLUMINATED EVEN THOUGH WE HAD SELECTED STOW. THE AIRPLANE AGAIN HAD A R ROLLING TENDENCY; WHICH I WAS EASILY ABLE TO OVERCOME WITH AILERON INPUTS. WE LANDED NORMALLY WITHOUT FURTHER INCIDENT. AFTER LNDG INSPECTION REVEALED THE L SPOILER WAS MISSING RIVETS AND HAD CRACKED IN THE MIDDLE. THE OUTBOARD HALF WAS BENT AFT AT THE CRACK. I COMPLETED THE NORMAL MAINT AND DISPATCH NOTIFICATIONS AND NOTIFIED MY CHIEF PLT OF THE MALFUNCTION BY TELEPHONE.