B727-200 AILERON CTLS LOCK UP AFTER FLYING THROUGH HVY TURB DURING DSCNT FOR LNDG. FLC DECLARED AN EMER AND AFTER A HARD LNDG; THE AILERONS WERE FREE.

Narrative

SHORTLY AFTER STARTING DSCNT FROM FL240; WE ENCOUNTERED 2 SHARP JOLTS OF HVY CHOP. THE SECOND ONE HAD A LOUD BANG WITH IT INSIDE THE AIRPLANE. AS WE BEGAN TO MANEUVER FOR LNDG; THERE WAS A RACHETING SOUND AND THE AILERONS WERE NOT FUNCTIONING. WE DECLARED AN EMER AND REQUESTED EQUIP AND MADE A NORMAL LNDG. THE LNDG WAS FIRM BECAUSE OF A LIGHT TAILWIND AND THIS APPARENTLY JARRED WHATEVER WAS BINDING THE AILERONS LOOSE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE ACFT AILERON ASSEMBLY WAS TAKEN APART IN AN EFFORT TO FIND THE PROB; BUT NONE WAS FOUND. HE THEN TEST FLEW THE ACFT AND FOUND THAT THE AILERON AUTOPLT SERVO WOULD SOMETIMES NOT DISENGAGE WHEN SHUTTING OFF THE AUTOPLT. WHEN THIS HAPPENED; THE AILERONS COULD ONLY BE MOVED A SMALL AMOUNT; MAKING BANKS VERY DIFFICULT. FOR THIS REASON; HE CHOSE TO LAND STRAIGHT AHEAD WITH A TAILWIND INSTEAD OF CIRCLE-TO-LAND. HOWEVER; THE JAR OF THE LNDG TOUCHDOWN MUST HAVE CAUSED THE ELECTRICAL SOLENOID TO BE ACTIVATED IN THE CLOSED POS AND SHUT OFF THE AILERON SERVO.