Event Overview
On 23 October 2013 at 0540 hrs, a DHC-8-402 Dash 8, registered G-JECJ, experienced a number of cautions and warnings on the Central Warning Panel (CWP) while en-route. The number of these increased, and cabin and cockpit lights also started to fail. The aircraft diverted to Manchester Airport, where an uneventful landing was made.
Manufacturer Findings
Subsequent to the initial bulletin, the aircraft manufacturer provided findings from their examination of components:
- The brushes and collector of the DC generator were found severely worn and damaged.
- No fault was found with the Generator Line Contactor (GLC) K2.
- No fault was found with the DC Generator Control Unit (GCU).
Conclusion from Manufacturer
The report concluded that the loss of contact between the brushes and armature, while backed up by the battery, allowed the condition to be undetected by normal generator power quality protection circuits. In the absence of detection, the GCU and EPCU do not reconfigure the system as would be the case for a power quality failure.
Pilot Detection and Remedial Action
The manufacturer noted that this failure mode is detectable by the pilot through observation of zero generator output current on the electrical load meter page. Additionally, abnormal positive discharge current from the battery when the generator is believed to be on-line is an indication of impending battery depletion. Resumption of DC power to the right DC buses could be accomplished by turning off the DC Generator switch to the faulty side, which will enable cross tying of the opposite side to supply the load as well as charging the battery.
Proposed AFM Amendment
Bombardier advised that they propose an amendment to the Aircraft Flight Manual (AFM) to address this condition.