Discussion
What events have caused this AD? In December 1985, Snow Engineering Co. issued Service Letter 62 to recommend the inspection of eyebolts. This was in response to several reports of eyebolt failures on Models AT-301 and AT-400 airplanes.
In response to another failure of an eyebolt on an AT-400 airplane, Snow Engineering Co. issued Service Letter 129 in September 1994. This service letter recommended eyebolt replacement every 2,000 hours time-in-service (TIS) for Models AT-301 and AT-400 airplanes. After a report of an eyebolt failure on a Model AT-602 airplane, Snow Engineering Co. revised Service Letter 129 in November 2003 to recommend replacing eyebolts for Models AT-602, AT-802, and AT-802A airplanes every 1,350 hours TIS.
In December 2003, FAA issued Special Airworthiness Information Bulletin (SAIB) CE-04-23. This SAIB recommended periodic eyebolt replacement following Snow Engineering Co. Service Letter 129.
In April 2004, we received a report of both eyebolts that attach the left hand stabilizer failing in flight on a Model AT-602 airplane. These eyebolts had accumulated 1,675 hours TIS.
Engineering analysis concludes that the eyebolts failed as a result of high-cycle, low-nominal stress. This is most likely due to the loss of torque during service.
Air Tractor has since redesigned the horizontal stabilizer structure for Models AT-802 and AT-602 airplanes to accommodate a new, stronger eyebolt.
Snow Engineering Co. also revised Service Letter 129 with new eyebolt replacement intervals and issued Service Letter 129A to include procedures for optional replacement of the steel brace assembly inside the stabilizer with a new steel brace assembly with larger bushings to accommodate new stronger eyebolts on existing Models AT-602, AT-802, and AT-802A airplanes. This modification provides for increased safety and extends eyebolt replacement intervals.
What is the potential impact if FAA took no action? Failure of an eyebolt could lead to an abrupt change or complete loss of pitch control and/or aircraft departure from controlled flight.
Has FAA taken any action to this point? We issued a proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that would apply to certain Air Tractor, Inc. (Air Tractor) Models AT-300, AT-301, AT-302, AT-400, AT-400A, AT-401, AT- 402, AT-602, AT-802, and AT-802A airplanes. This proposal was published in the Federal Register as a notice of proposed rulemaking (NPRM) on March 4, 2005 (70 FR 10513). The NPRM proposed to require you to repetitively tighten the four eyebolts that attach the front and rear spar of the horizontal stabilizer to the respective stabilizer strut to the specified torque, and repetitively replace at specified intervals any eyebolts that attach the front and rear spar of the horizontal stabilizer to the respective stabilizer strut. An option for replacing the steel braceassembly inside the stabilizer with a new steel brace assembly with larger bushings and stronger eyebolts that increases the interval for replacement of eyebolts for AT-602, AT-802, and AT-802A airplanes was also included in this proposed AD.
Comments
Was the public invited to comment? We provided the public the opportunity to participate in developing this AD. The following presents the comments received on the proposal and FAA's response to each comment:
Comment Issue No. 1: Correct the Date for Service Letter 129 in Discussion
What is the commenter's concern? One commenter writes that the original date of Snow Engineering Co. Service Letter 129 is September 1994 (not September 1995) and requests use of the correct date in the Discussion section.
What is FAA's response to the concern? We concur. We will correct all reference in the final rule of the service letter to read, "Snow Engineering Co. issued Service Letter 129 in September 1994."
Comment Issue No.2: Cases of Cracks in Model AT-802 Airplane Eyebolts
What is the commenter's concern? Mr. Leland Snow, Air Tractor, Inc., writes that the Discussion section of the NPRM is incorrect in reporting, "The FAA also received two service difficulty reports (SDRs) in November 2003. Both SDRs referenced Model AT-802 airplane eyebolt cracks." Also, Mr. Snow notes that Air Tractor inspected eyebolts that were reported to be cracked and found that the eyebolts were not cracked but instead had a groove caused by washer edge contact.
What is FAA's response to the concern? The FAA is not able to verify with certainty that the eyebolts that Air Tractor inspected are the same or not as those eyebolts identified in the two SDRs. However, both the eyebolts Air Tractor inspected and the eyebolts reported to FAA were from the same sources, making Air Tractor's claim a strong possibility.
We have deleted the reference to the two SDRs from the Discussion section of the final rule.
CommentIssue No. 3: Initial and Repetitive Tightening of the Eyebolts
What is the commenter's concern? Mr. Leland Snow, Air Tractor, requests that the compliance times for initial and repetitive tightening of the eyebolts follow the times required in Snow Engineering Service Letter 129, initial inspection and tightening of the eyebolts within 100 hours TIS, and repetitively tighten the eyebolts every 12 calendar months thereafter.
What is FAA's response to the concern? We agree to add the requirement to initially inspect within 100 hours TIS after the effective date of the AD. However, we will retain the initial 12 calendar months requirement with whichever occurs first as the prevalent time. We agree the repetitive inspections should remain every 12 calendar months thereafter.
Conclusion
What is FAA's final determination on this issue? We have carefully reviewed the available data and determined that air safety and the public interest require adopting the AD as proposed except for the changes discussed above and minor editorial corrections. We have determined that these changes and minor corrections:
--Are consistent with the intent that was proposed in the NPRM for correcting the unsafe condition; and
--Do not add any additional burden upon the public than was already proposed in the NPRM.
Changes to 14 CFR Part 39--Effect on the AD
How does the revision to 14 CFR part 39 affect this AD? On July 10, 2002, the FAA published a new version of 14 CFR part 39 (67 FR 47997, July 22, 2002), which governs the FAA's AD system. This regulation now includes material that relates to altered products, special flight permits, and alternative methods of compliance. This material previously was included in each individual AD. Since this material is included in 14 CFR part 39, we will not include it in future AD actions.
Costs of Compliance
How many airplanes does this AD impact? We estimate that this AD affects 1,011 airplanes in the U.S. registry.
What is the cost impact of this AD on owners/operators of the affected airplanes? We estimate the following costs to do the tightening of the four eyebolt nuts to the specified torque:
Labor cost
Parts cost
Total cost per airplane
Total cost on U.S. operators
1 workhour $65 per hour = $65
No parts required
$65
$65 1,011= $65,715
We estimate the following costs to do any necessary replacement of the four eyebolts for the Models AT-300, AT-301, AT-302, AT-400, AT- 400A, AT-401, AT-402 AT-602, AT-802, and AT-802A airplanes:
Average labor cost
Average parts cost
Average total cost per air-plane
Average total cost on U.S. operators
1 workhour $65 per hour = $65
$186.30
$251.30
1,011 $251.30 = $254,064.30
We estimate the following costs to do any necessary replacement of the steel brace assembly inside the stabilizer with a new steel brace assembly with larger bushings on existing Models AT-602, AT-802, and AT-802A airplanes:
Average labor cost
Average parts cost
Average total cost per air-plane
Average total cost on U.S. operators
22 workhours $65 per hour = $1,430
$901.65
$2,331.65
312 $2,331.65 = $727,474.80
Authority for This Rulemaking
What authority does FAA have for issuing this rulemaking action? Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, Section 106 describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the agency's authority.
We are issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701, "General requirements." Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within thescope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this AD.
Regulatory Findings
Will this AD impact various entities? We have determined that this AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect 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.
Will this AD involve a significant rule or regulatory action? For the reasons discussed above, I certify that this AD:
1. Is not a "significant regulatory action" under Executive Order 12866;
2. Is not a "significant rule" under the 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.
We prepared a summary of the costs to comply with this AD (and other information as included in the Regulatory Evaluation) and placed it in the AD Docket. You may get a copy of this summary by sending a request to us at the address listed under ADDRESSES. Include "Docket No. FAA-2004-19837; Directorate Identifier 2004-CE-43-AD" in your request.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, under 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.
Sec. 39.13 [Amended]
2. FAA amends Sec. 39.13 by adding a new AD to read as follows: