FAA PROPOSES AIRWORTHINESS DIRECTIVE ON PIPER WING SPARS requiring the inspection for metal fatigue of main wing spars on numerous Piper PA–28 and PA–32 single-engine airplanes that have reached a certain factored time-in-service level. The FAA estimated that two hours of work would be required to comply with the mandate to calculate the factored service hours of an airplane. Conditional costs to perform an inspection and to replace nuts and bolts were estimated at $147.50 per wing spar. The cos