DHC-8-400 FLT CREW REPORTS UNCOMMANDED RAPID LANDING GEAR CYCLING DURING DESCENT FROM FL240 AT 280 KNOTS. GEAR DOORS NEVER ACTUALLY OPEN.

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JUST AFTER STARTING OUR DSCNT; I NOTICED THAT BOTH MAIN LNDG GEAR DOOR LIGHTS CAME ON THEN OFF; THEN BOTH MAIN LNDG GEAR IN TRANSIT LIGHTS CAME ON THEN OFF; THEN BOTH MAIN LNDG GEAR DOOR LIGHTS CAME ON THEN OFF AGAIN. THIS SEQUENCE HAPPENED VERY QUICKLY; AS I JUST HAPPENED TO BE LOOKING AT THEM WHEN IT HAPPENED. THE CAPT DID NOT SEE THE LIGHTS BUT HAD HEARD THE NOISE FOR THE GEAR CYCLING. AT NO TIME DID EITHER OF US TOUCH THE GEAR HANDLE. THE CAPT THEN CONFERRED WITH MAINT CTL AND CONFERRED WITH ME AS TO AN APPROPRIATE COURSE OF ACTION. WE BOTH AGREED THAT WE WOULD PERFORM AN ALTERNATE GEAR EXTENSION AND THAT WE WOULD NOT DECLARE AN EMER UNLESS WE GOT AN UNSAFE INDICATION AFTER WE ATTEMPTED THE PROC. ALSO WE AGREED THAT IT WOULD BE PRUDENT TO HAVE EMER SVCS ON STANDBY. THE CAPT THEN CONTACTED ATC WITH OUR REQUESTS AND MADE ANNOUNCEMENTS TO THE FLT ATTENDANTS AND PAX. WE THEN PERFORMED THE ALTERNATE GEAR EXTENSION PROC AND GOT 3 GREEN LIGHTS FOR THE GEAR AND LANDED WITHOUT INCIDENT. THE CAPT DID AN EXCELLENT JOB HANDLING THE SITUATION WITH EXCELLENT CRM. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER WAS UNABLE TO PROVIDE ANY ADDITIONAL INFORMATION CONCERNING THE CAUSE OF THIS INCIDENT. THE FLT CREW RECEIVED A LATE DESCENT CLEARANCE AND THE ACFT WAS AT MAXIMUM INDICATED AIRSPEED IN AN ATTEMPT TO GET BACK ON PROFILE.