Events Leading to the Issuance of This AD
A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to supersede AD 96-09-08 R1, Amendment 39-9690 (61 FR 35936, No. 132, July 9, 1996), that applies to Aviat Models S-2A, S-2B, and S-2S airplanes (formerly Pitts Models S-2A, S-2B, and S-2S), was published in the Federal Register on May 30, 1997 (62 FR 29309). AD 96-09-08 R1 currently requires repetitively inspecting the longerons around the rear cabane struts for cracks on Aviat Models S-2A (all serial numbers (S/N)), S-2B (S/N 5000 through 5350), and S-2S (all S/N), and repairing and reinforcing any crack found during the inspections. The proposed AD would supersede AD 96-09-08 R1 with a new AD that would require:
(1) Repetitively inspecting the upper longerons aft of the rear cabane struts and forward of the instrument panel for cracks;
(2) Modifying any cracked longeron found during any inspection required by the proposed AD by incorporating Aviat Kit No. S-2-513;
(3) Inserting the revisions referenced in the Aviat SB No. 24, Revised: November 22, 1996 into the AFM; and
(4) Accomplishing one of the following:
-- Installing a redlined accelerometer marked at the +6g and -3g hash marks indicating the acrobatic "g" force limitations and a placard (part number 2-7604-47) stating the "g" force limitations; or
-- Fabricating and installing a placard in the pilot s clear view using at least 1/8-inch letters that incorporate the words:
"ACROBATIC MANEUVERS
PROHIBITED."
Accomplishment of this action would be in accordance with the Aviat Aircraft Inc. Service Bulletin No. 24, Revised: November 22, 1996, and Aviat Aircraft Inc. Installation Instructions to Kit No. S-2-513, dated August 26, 1996; Revised May 9, 1997.
Comments
Interested persons have been afforded an opportunity to participate in the making of this amendment. Several comments were received on the proposed rule.Due consideration has been given to the following comments.
A commenter suggested that the Aviat Pitts Model S-2A be eliminated from the applicability of the action because the aircraft does not have enough horsepower to sustain airspeeds that will damage the airframe structure.
The FAA does not concur. The FAA is obligated to address the whole fleet (all models) since it is possible to exceed the fatigue limits on all models regardless of horsepower. The aircraft weight and maneuver entry speed is the factor that drives the resultant gravity ("g") load. All of the Aviat models addressed can enter a snap roll while in a dive with the airspeed higher than the recommended entry speed. The final rule will not be changed as a result of this comment.
A commenter wanted the FAA to withdraw the NPRM because no fleet-wide problem exists.
The FAA does not concur. The reason this action was taken is because of four known incidents where cracked longerons were the cause. After additional investigation, tests showed that exceeding the "g" force limitations causes stress to the longerons, thus producing cracks. Therefore, the FAA is requiring additional measures to assure that the operation of the affected airplanes does not exceed the certification limits. The FAA also wants to assure that the affected airplanes are flying without cracks. If the upper longerons are not repetitively inspected for cracks, then the airplane is susceptible to an unsafe condition. The final rule will not be changed as a result of this comment.
One commenter suggested that the frequency of the longeron inspection occur at every 100-hour time-in-service (TIS) intervals.
The FAA concurs and notes that a 100 hour TIS interval for repetitive inspections of the upper longeron area was proposed in the NPRM. The final rule will not be changed as a result of this comment.
A commenter wants the "g" limitation placard to read "+4.5g and -2.5g while performing a snap rollmaneuver" because the twisting forces imposed on the airframe by snap rolls are more likely to cause structural failure than straight positive "g" force.
The FAA does not concur. There has been no convincing analysis to indicate that anything less than the original certificated maximum "g" force levels of +6 and -3 should not be the airplane operating limits. The final rule will not be changed as a result of this comment.
Another commenter suggested inspecting the fuselage for structural damage if a "g" factor of +6 is exceeded during landing. The commenter did not provide any justification to support this argument. As a result, this comment will not change the final rule.
One commenter wanted a requirement to mark the accelerometers at the operating limitations. The FAA agrees. This requirement was proposed in the NPRM. The final rule will not change as a result of this comment.
A commenter suggested delaying the final rule pending further study of the effect of snap roll maneuvers because the AD does not recognize or discuss the twisting forces imposed on the airframe by snap rolling maneuvers, and that the snap roll maneuvers result in a higher "g" force than straight positive "g" forces.
The FAA does not concur. Flight test analysis shows that the original operating limits that were determined during certification of these airplanes are adequate as long as the operator flies the airplane within the "g" force limits. The final rule will not change as a result of this comment.
Another comment requested that the FAA delete the requirement for the placard on the accelerometer. No justification was presented for this request. The FAA has determined that this placard is necessary to fully address the unsafe condition. The final rule will not change as a result of this comment.
One comment recommended amending the aircraft documents to reflect a mandatory VNE (never exceed speed) for snap roll maneuvers to limit the "g" force loads. The commenter presented no justification for this recommendation.
The FAA does not concur. This recommendation offers no benefit over the already proposed placard placed near the accelerometer because the flight manual already states the certificated operating "g" limits and entry speeds for maneuvers.
Aviat Aircraft Inc. commented that they agree with the need for the AD, but Aviat felt that the general theme of the preamble to the NPRM was degrading and made hostile references to the Aviat airplanes. Aviat submitted a re-written preamble to NPRM. The FAA did not re-print this submission as part of the final rule comments because the comments made did not speak to the AD only to the discussion in the preamble of the NPRM. The preamble to the NPRM is not published as part of the final rule. Therefore, this final rule is not changed as a result of this comment. The document submitted can be obtained by written request to the Office of the Regional Counsel s Rules Docket found in the ADDRESSES section of this AD.
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 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 500 airplanes in the U.S. registry will be affected by this AD, that it will take approximately 8 workhours per airplane to accomplish the initial inspection and modification, and that the average labor rate is approximately $60 an hour. The installation of the revisions to the AFM and the placard may be performed by the owner/operator holding at least a private pilot certificate as authorized by section 43.7 and 43.9 of the Federal Aviation Regulations (14 CFR 43.7 and 43.9). Therefore, the only labor cost associated with this step is the time of the owner/operator. Parts costs are estimated to be approximately $400 for Aviat Kit No. S-2-513 and $10 for the placard. Based on these figures, the total cost impact of this AD on U.S. operators is estimated to be $445,000 or $890 per airplane. The estimated cost does not account for the repetitive inspections because the FAA has no way to determine the number of repetitive inspections that might be incurred over the life of the airplane. The manufacturer has informed the FAA that they have distributed kits to reinforce 4 airplanes. With this in mind, the approximate cost for this AD on U.S. operators will be reduced from $445,000 to $441,440.
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 ofgovernment. 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 USC 106(g), 40113, 44701.
39.13 [Amended]
2. Section 39.13 is amended by removing airworthiness directive (AD) 96-09-08 R1, Amendment No. 39-9690 and by adding a new AD to read as follows: