Mufflers

摘要

Pilot observed smoke in the cockpit, declared emergency and landed normally. Inspection of the right engine compartment revealed the muffler's aft wall was missing and exhaust was directed onto the battery box. Hot exhaust melted the battery and battery contactor, clock fuse holder, both battery cables and boots. The gascolator push/ pull control knob was melted. All electrical wiring in the engine compartment was destroyed. The owner recalls engine backfiring when a student performed the ignition test IAW AD 76-07-12 at too high an rpm, which likely aggravated an already weak muffler (p 04504004), causing the failure.