AD 97-23-04

Discussion The Federal Office for Civil Aviation (FOCA), which is the airworthiness authority for Switzerland, recently notified the FAA that an unsafe condition may exist on Pilatus Models PC-12 and PC-12/45 airplanes. The FOCA reports an instance of abnormal automatic engagement of the fuel booster pumps during normal operation of a Pilatus Model PC-12 airplane. The FOCA's investigation reveals that the fuel tank inward vent valves may fail in the closed position under certain conditions. Moisture ingestion, followed by cold soak, can lead to the fuel tank inward vent valve freezing. This condition, if not corrected, could result in wing airfoil distortion and structural damage with consequent degradation of the airplane's handling qualities.

Relevant Service Information Pilatus issued Service Bulletin No. 28-003, Revision 1, dated September 30, 1997, which specifies procedures for replacing the fuel tank vent valves with modified fuel tankvent valves.

The FOCA of Switzerland classified this service bulletin as mandatory and issued Swiss AD HB 97-432A, dated October 3, 1997, in order to assure the continued airworthiness of these airplanes in Switzerland.

The FAA's Determination This airplane model is manufactured in Switzerland and is type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the FOCA of Switzerland has kept the FAA informed of the situation described above.

The FAA has examined the findings of the FOCA of Switzerland; reviewed all available information, including the service bulletin referenced in this document; and determined that AD action is necessary for products of this type design that are certificated for operation in the United States.

Explanation of the Provisions of This AD Since anunsafe condition has been identified that is likely to exist or develop in other Pilatus Models PC-12 and PC-12/45 airplanes of the same type design registered for operation in the United States, the FAA is issuing an AD. This AD requires replacing the fuel tank vent valves with modified fuel tank vent valves. Accomplishment of the replacement is required in accordance with Pilatus Service Bulletin No. 28-003, Revision 1, dated September 30, 1997.

Determination of the Effective Date of the AD Since a situation exists (possible wing airfoil distortion and structural damage with consequent degradation of the airplane's handling qualities) that requires the immediate adoption of this regulation, it is found that notice and opportunity for public prior comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.

Comments Invited Although this action is in the form of a final rule that involves requirements affectingimmediate flight safety and, thus, was not preceded by notice and opportunity to comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications should identify the Rules Docket number and be submitted in triplicate to the address specified above. All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket No. 97-CE-95-AD." The postcard will be date stamped and returned to the commenter.

Regulatory Impact The regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

The FAA has determined that thisregulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and is not a significant regulatory action under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket (otherwise, an evaluation is not required). A copy of it, if filed, may be obtained from the Rules Docket.

List of Subjects in 14 CFR Part 39 Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

Adoption of the Amendment Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39)as follows:

PART 39 - AIRWORTHINESS DIRECTIVES 1. The authority citation for part 39 continues to read as follows: Authority: 49 USC 106(g), 40113, 44701.

39.13 [Amended] 2. Section 39.13 is amended by adding a new airworthiness directive (AD) to read as follows: