LGT EXPERIENCES VIBRATION WHEN SPD BRAKES STOWED.

Narrative

A VERY NOTICEABLE VIBRATION OCCURRED DURING CRUISE. VIBRATION STOPPED WHEN SPD BRAKES WERE EXTENDED EVEN A VERY SMALL AMOUNT FROM THE STOWED POS. VIBRATION BEGAN AGAIN WHEN SPD BRAKE LEVER STOWED. SO CHKED WINGS FOR SPOILER CAUSING THE VIBRATION BUT COULD NOT SEE THE CAUSE. I ADVISED OUR DISPATCHER AND MAINT COORDINATOR OF THE DISCREPANCY AND THAT WE WERE GOING TO FOLLOW A SPOILER FLOAT CHKLIST WHICH CALLED FOR A FLAPS 15 DEG LNDG. I ALSO ADVISED THEM WE WOULD DECLARE AN EMER WITH APCH CTL. THE DISPATCHER SAID HE WOULD CALL CVG APCH CTL AND ADVISE THEM TO EXPECT THE SIT. THE SPOILER FLOAT CHKLIST CALLED FOR US TO ISOLATE (STOP HYD PRESSURE TO) THE SPOILERS CAUSING THE PROB BUT WE WERE NEVER ABLE TO DO THIS AS WE COULD NOT VISUALLY IDENT THEM AND ALSO THE VIBRATION STOPPED DURING DSCNT. WE CONTINUED TO USE THE SPOILER FLOAT CHKLIST AS MUCH AS WE COULD AND MADE A FLAPS 15 DEG LNDG. WE ALSO DECLARED AN EMER WITH APCH CTL. FO FLEW THE APCH AND LNDG WHICH WERE UNEVENTFUL. EMER TERMINATED AFTER LNDG. I WAS READY TO ISOLATE THE SPOILERS SHOULD A CTL PROB DEVELOP; WHICH IT NEVER DID. THIS COULD HAVE BEEN CALLED A 'PRECAUTIONARY EMER' IF THERE WERE SUCH AN OCCASION AS WE COULD HAVE USED A NORMAL CHKLIST AND APCH ETC; SINCE THE VIBRATION STOPPED DURING DSCNT AND WE NEVER HAD UNCOMMANDED CTL INPUTS. HOWEVER I FELT TO BE ON THE SAFE SIDE IT WAS BETTER TO CONDUCT THE FLT AS WE DID.