What was found
AN APU TAILPIPE FIRE OCCURRED DURING APU STARTUP. THE APU HAD HEAT DAMAGE. THE AFT AND LT SIDE OF THE FUSELAGE TAIL CONE INSTALLATION (P/N 65-46577-569) ALSO SUFFERED HEAT DAMAGE, AS WELL AS THE LWR I/B 2 FT OF THE LT ELEVATOR (P/N 65C25746-131) & LOWER I/B 2 FT OF THE LT ELEVATOR TAB (P/N 65C26384-23). *S/D* REPLACED THE APU, APU TAILPIPE, FUSELAGE TAIL CONE SECTION, LT ELEVATOR AND ELEVATOR TAB ASSEMBLIES. APU QUILL SHAFT FAILURE WAS CAUSE OF THE INCIDENT. APIC S/B 170101-49-82 & 170101-49-85 ADDRESS THE QUILL SHAFT FAILURE AND HAVE BEEN APPROVED FOR USE ON UAL APU'S. FADEC SOFTWARE V16.1 S/B 171254-49-8 HAS BEEN RELEASED BY BOEING AND SUNDSTRAND ON 12-7-98 AND WILL BE IMPLEMENTED IN THE UAL FLEET.