Airworthiness Directives; Aerospace Welding Minneapolis, Inc. Mufflers

We propose to adopt a new airworthiness directive (AD) for certain Aerospace Welding Minneapolis, Inc. mufflers, part numbers A1754001-23 and A1754001-25, installed on Textron Aviation Inc. (type certificate previously held by Cessna Aircraft Company) Models 172, 172R, 172S, and 177 airplanes. This proposed AD was prompted by occurrences of cracks or broken welds in the connecting weld of the muffler body to muffler cuff that may allow carbon monoxide exhaust fumes into the cockpit heating system. This proposed AD would require an inspection of the muffler for leaking to identify cracks and replacement of the muffler. We are proposing this AD to correct the unsafe condition on these products.