What was found
ON APU START, FLAMES REPORTED COMING OUT OF REAR OF AIRCRAFT. APU SHUT DOWN WITH FAULT LIGHT. [07-06-07] REFERENCE SERVICE TIP 49-00-02 PG 200A. PROBABLE CAUSES ARE IF THE APU HAS BEEN SHUTDOWN FOR A TIME LESS THAN ONE HOUR OR IF THE PRE-START EXHAUST GAS TEMPERATURE (EGT) IS GREATER THAN 100 DEGREES F AND/OR RESIDUAL FUEL IN THE COMBUSTOR PRIOR TO STARTING. THE BRIEF FLAME DOES NOT POSE ANY OPERATIONAL RISK TO THE AIRCRAFT.