Aircraft Mufflers

Pilot observed smoke in the cockpit, declared emergency and landed normally. Inspection of the right engine compartment revealed the mufflers 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.

Editorial Staff

Thursday, September 15, 2016 at 12:00 AM ET

Verified

Key Takeaways:

Aircraft exhaust systems, particularly mufflers, are prone to various failures including wall breaches, cracked welds, internal separations, and missing components.
These failures pose significant safety risks, leading to incidents such as smoke in the cockpit, carbon monoxide warnings, and extensive damage to critical adjacent aircraft systems like batteries and wiring.
Contributing factors to these failures include design flaws (e.g., insufficient clearance causing chafing), operational issues (e.g., engine backfiring during tests), and general material fatigue or issues stemming from previous repairs.

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Cessna Model 150E
Aft Muffler Wall Failure

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/n 04504004), causing the failure.