AD/BEECH 1900/12 - Pneumatic Air System Plumbing

This Directive supersedes and cancels AD/BEECH 1900/6 which mandated certain modification of the instrument/pneumatic air system. Following eight additional reports of moisture freezing in the pneumatic air system plumbing of Model 1900 and 1900C aircraft, fitted with the same modification as that required by AD/BEECH 1900/6, the FAA determined that further modifications were required. Recent testing of the Model 1900D by the FAA also indicates that the design of the pneumatic air system on these aircraft is also conducive to moisture freezing. Actions specified by this Directive are designed to prevent ice formation in the pneumatic air system, which, if not detected, could result in the vacuum for the deice boot operation being unavailable which could result in the subsequent loss of the aircraft.