AD 98-09-25

Events Leading to the Issuance of This AD A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that would apply to certain Piper Models PA-31, PA-31-300, PA-31-325, and PA-31-350 airplanes was published in the Federal Register as a notice of proposed rulemaking (NPRM) on August 22, 1997 (62 FR 44597). The NPRM proposed to require replacing the lower spar splice plate and reworking the lower spar caps. Accomplishment of the proposed action as specified in the NPRM would be required in accordance with Piper Main Spar Splice Plate Replacement (Lower) Kit No. 766-641, Drawing 88255, Revision A, dated May 12, 1997; or Piper Main Spar Splice Plate Replacement (Lower) Kit No. 766-640, Drawing 88254, Revision A, dated May 12, 1997.

The NPRM was the result of numerous reports of fretting and cracking of the lower spar splice plates on Piper PA-31 series airplanes in Australia, and a report of one incident in the United States.

Interested persons have been afforded an opportunity to participate in the making of this amendment. No comments were received on the proposed rule or the FAA's determination of the cost to the public.

The FAA has received data from the Australian Civil Aviation Safety Authority (CASA), which was based on the analysis of 34 airplanes. This data shows the lower spar splice plate replacement threshold as the following:

- 6,000 hours time-in-service (TIS) for Models PA-31, PA-31-300, and PA-31-325 airplanes; and

- 13,000 hours TIS for Model PA-31-350 airplanes.

The lower spar splice plate replacement threshold was presented as 2,500 hours TIS in the NPRM. The FAA conducted statistical analysis on this data received from the Australian CASA. This analysis shows that the thresholds presented by the Australian CASA are reliable and accurate.

The FAA's Determination After careful review of all available information related to the subject presented above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed except for the change in the compliance time (from 2,500 hours TIS to 6,000 hours TIS or 13,000 hours TIS, as applicable) and minor editorial corrections. The FAA has determined that these minor corrections will not change the meaning of the AD and will not add any additional burden upon the public than was already proposed.

Cost Impact The FAA estimates that 1,700 airplanes in the U.S. registry will be affected by this AD, that it will take approximately 8 workhours per airplane to accomplish this replacement, and that the average labor rate is approximately $60 an hour. Parts cost approximately $210 per airplane. Based on these figures, the total cost impact of this AD on U.S. operators is estimated to be $1,173,000, or $690 per airplane.

Piper has informed the FAA that, as of August 22, 1997 (the publication date of the NPRM), parts have been distributed to equip 1 affected airplane. Presuming that this set of parts is installed on an affected airplane, the cost impact of this AD will be reduced by $690, from $1,173,000 to $1,172,310.

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.

For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A copy of the final evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting the Rules Docket at the location provided under the caption "ADDRESSES".

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 U.S.C. 106(g), 40113, 44701.

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