William Davis

Subject: Docket No. FAA?2006?24825; Directorate Identifier 2006?NE?17?AD Sirs, Regarding the recent notice of proposed rulemaking (NPRM) proposing to supersede an existing airworthiness directive (AD): The "Costs of Compliance" paragraph - "We estimate that this proposed AD would affect 30 RRD Dart 528, 529, 532, 535, 542, and 552 series turbofan engines installed on airplanes of U.S. registry." appears to be in error. These are turboprop engines. The "Applicability" paragraph, (c), of the proposed airworthiness directive appears to have omitted some models. STC SA1054WE modified General Dynamics Convair Model 240 aircraft for installation of Rolls Royce Dart RDa 10 Mark 542-4 engines (GD/Convair 240D or Model 600 or 600-240D) and STC SA1096WE modified General Dynamics Convair Model 340/440 aircraft for installation of Rolls Royce Dart RDa 10 Mark 542-4 engines (GD/Convair 340D/440D or Model 640 or 640-340D and 640-440D). These aircraft can still be found in the FAA's registry database.