Suspected Unapproved Parts Details
On July 25, 2013, an inadvertent feather event occurred shortly after takeoff on a DeHavilland DHC-8-100 series aircraft. Flight data records indicated that the #1 PCU beta switch was closed and lit during takeoff when a beta condition did not exist. During this event, the switch remained closed as the propeller transitioned above the ground handling range during takeoff. This condition resulted in a propeller over-torque when the aircraft’s beta backup system became active and commanded the propeller to feather while the engine was in a high-power condition. Examination of the subject PCU revealed that the beta light assembly was installed incorrectly, deforming the switch case. A deformed switch case can adversely affect switch function reliability and cause the switch mechanism to malfunction. The malfunction could manifest as a failed closed switch or by an intermittent delayed opening of the switch. Group of units that was discovered after the issue of SAFO 13009 that had been repaired/overhauled by PPI between June 4, 2001 and July 11, 2003. This group of units PPI is unable to identify the specific customers who may have these units installed and in service, thus the need to recommunicate to the aviation community the broader scope of the safety matter.
