As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAILED TO START - SMOKE OBSERVED FROM EXHAUST DURING START. PLACED ON MEL 49-00-1. CLEARED 8/27. INTERROGATED CDS, FOUND MULTIPLE HITS FOR FAULT "055/2 IGNITER PLUG B OPEN" IN FAULT HISTORY. REPLACED BOTH IGNITERS REF Q400 AMM 49-40-04-000-801 AND 49-40-04-400-801. OPS TEST GOOD. CLEARED MEL. RETURNED TO SERVICE.