Narrative:

The air intake filter assembly with landing light departed aircraft in flight. The bolt was found in its original hole location; the muffler assembly prevented it from moving. The bolt was secured with assembly with elastic nut plate. Threads showed evidence of proper tightening; no rust on threads. Aircraft sat dormant for a few months. No provisions for safety wire of bolt inside nose cowling. Backfire might have caused the elastic stop nut to fail; throwing the assembly into propeller and damaging left-hand side cowling fiberglass. Pilots reported pattern work; improper leaning of mixture and/or throttle jocking could have caused the backfire; a lean mixture and/or carburetor heat; maybe sudden throttle movements. Fiberglass a metal tab into nose cowl to secure a drilled head bolt; or an alternate means of safety wire for filter assembly attach bolt. Check security to filter assembly every pre-flight.

Related reports:

Google
 

Original NASA ASRS Text

Title: An Inspection Authority (IA) Rated Technician reports the air intake filter assembly with landing light departed a Piper-28 aircraft in flight. Backfire may have caused an elastic stop nut to fail; throwing the assembly into propeller and damaging left side cowling fiberglass.

Narrative: The air intake filter assembly with landing light departed aircraft in flight. The bolt was found in its original hole location; the muffler assembly prevented it from moving. The bolt was secured with assembly with elastic nut plate. Threads showed evidence of proper tightening; no rust on threads. Aircraft sat dormant for a few months. No provisions for safety wire of bolt inside nose cowling. Backfire might have caused the elastic stop nut to fail; throwing the assembly into propeller and damaging left-hand side cowling fiberglass. Pilots reported pattern work; improper leaning of mixture and/or throttle jocking could have caused the backfire; a lean mixture and/or carburetor heat; maybe sudden throttle movements. Fiberglass a metal tab into nose cowl to secure a drilled head bolt; or an alternate means of safety wire for filter assembly attach bolt. Check security to filter assembly every pre-flight.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.