As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAILED TO START. FAULT LIGHT ILLUM AND EICAS MSG. APU FAULT DISPLAYED. SECOND ATTEMPT INDICATES (SLOW ACCEL, HUNG START). FOUND MISSING HARDWARE SENSOR ON LT SIDE OF APU PLENNUM. NONE STOCKED AT IAD. UNABLE TO DETERMINE IF THE LISTED PARTS WILL COMPLETE THE REPAIR AS IPC DOES NOT SHOW VIEW INSIDE THE PLENUM. THE APU WAS REPLACED.