What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
(-23) The aircraft was being used for a local part 91 orientation flight and touch & go landing practice. After the flight, the crew noticed a jagged hole in the wing skin, on the bottom of the right wing just forward of the right aileron. A semi-circular indentation was also found in the leading edge of one of the rear propeller blades. Subsequent investigation by company maintenance personnel revealed that a bolt (AN4-16A) and nut (MS21042L4) used to secure the rear engine muffler to a brace assembly were missing. Review of the airframe log revealed that the rear muffler had been replaced during a 100 hour inspection, the day before the flight, and about two flight hours earlier. The mechanic who signed the logbook entry was interviewed regarding the work. He reported that he had reinstalled the exising bolt with a new MS21042L4 self-locking nut, torqued it to "standard proper torque" and rechecked it for proper installation.
As the FAA filed it
(-23) THE AIRCRAFT WAS BEING USED FOR A LOCAL PART 91 ORIENTATION FLIGHT AND TOUCH & GO LANDING PRACTICE. AFTER THE FLIGHT, THE CREW NOTICED A JAGGED HOLE IN THE WING SKIN, ON THE BOTTOM OF THE RIGHT WING JUST FORWARD OF THE RIGHT AILERON. A SEMI-CIRCULAR INDENTATION WAS ALSO FOUND IN THE LEADING EDGE OF ONE OF THE REAR PROPELLER BLADES. SUBSEQUENT INVESTIGATION BY COMPANY MAINTENANCE PERSONNEL REVEALED THAT A BOLT (AN4-16A) AND NUT (MS21042L4) USED TO SECURE THE REAR ENGINE MUFFLER TO A BRACE ASSEMBLY WERE MISSING. REVIEW OF THE AIRFRAME LOG REVEALED THAT THE REAR MUFFLER HAD BEEN REPLACED DURING A 100 HOUR INSPECTION, THE DAY BEFORE THE FLIGHT, AND ABOUT TWO FLIGHT HOURS EARLIER. THE MECHANIC WHO SIGNED THE LOGBOOK ENTRY WAS INTERVIEWED REGARDING THE WORK. HE REPORTED THAT HE HAD REINSTALLED THE EXISING BOLT WITH A NEW MS21042L4 SELF-LOCKING NUT, TORQUED IT TO "STANDARD PROPER TORQUE" AND RECHECKED IT FOR PROPER INSTALLATION.