The FAA published two airworthiness directives this week that affect the Piper general aviation fleet. According to a report at AVweb.com, a final rule published on Monday affects 3,100 Piper Comanches, requiring inspections of the stabilator horn assembly, at a cost of about $1,000 per airplane. If the assembly needs to be replaced, it would cost another $1,600. Failure of the stabilator horn could lead to a loss of pitch control in flight, the FAA said. A proposed rule published on Tuesday affects about 1,000 Piper twins, which supersedes an existing AD that requires repetitive inspections of the exhaust system.