A DC9-30 IN CRUISE AT FL330 DIVERTED DUE TO FROZEN AILERONS CAUSED BY WATER PENETRATING THE AILERON SPOILER MIXERS THEN FREEZING AT ALTITUDE.

Narrative

DURING CRUISE FLT FROM ZZZ TO BOS THE CAPT NOTICED THE AILERON SERVO INDICATOR ON THE AUTOPLT WAS AT FULL RIGHT DEFLECTION. THE CTL YOKE WAS AT ALMOST NEUTRAL SO THE CAPT DISENGAGED THE AUTOPLT TO TROUBLESHOOT THE SERVO PROB. AT THIS TIME HE DISCOVERED THAT THE AILERONS WERE FROZEN IN PLACE. WITH MODERATE FORCE WE WERE ABLE TO FREE UP THE AILERONS BUT THEY STILL HAD A 'HEAVY RATCHETY' FEEL TO THEM. AFTER TALKING WITH OUR COMPANY MAINT ON THE RADIO WE DECIDED TO DIVERT TO ZZZ1. THE REMAINDER OF THE FLT WAS UNEVENTFUL EXCEPT FOR THE 'HEAVY' FEEL OF THE AILERONS. AFTER LNDG COMPANY MAINT FOUND EVIDENCE OF ICE AND WATER ON THE AILERON CTL CABLES AND MIXING ASSEMBLY. PRIOR TO OUR DEP OUT OF ZZZ; THE ACFT SAT IN HEAVY RAIN OVERNIGHT. THE WATER IN THE CABLE AREA WAS BELIEVED TO BE THE CAUSE OF THE PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AIRPLANE WAS PARKED OVERNIGHT IN ZZZ IN A HEAVY RAIN STORM. THE RPTR SAID WATER ENTERED THE OVERWING EMER EXIT AND FLOWED DOWN INTO THE MAIN WHEEL WELL AND POOLED ON THE SLANT PANEL COVERING THE AILERON-SPOILER MIXERS. THE RPTR STATED THE PROTECTIVE SLANT PANEL HAD A DEFECTIVE SEAL WHICH ALLOWED THE WATER TO SOAK THE L AND R AILERON-SPOILER MIXERS. THE RPTR SAID AT ALTITUDE THE WATER FROZE AND LOCKED UP THE AILERONS. THE RPTR STATED THAT AFTER CLEARING THE WATER AND ICE ON THE GND THE AIRPLANE OPERATED NORMALLY THE REMAINDER OF THE DAY.