Discussion
The FAA has received many service difficulty reports of failures of pivot assemblies on Cessna Model 172RG airplanes. Failure of the main landing gear pivots has resulted in gear-up landings or loss of braking. The end of the pivot experiences overload stress because of improper bushing clearance. This stress can produce fatigue cracks that spread until the pivot fitting fails, preventing the landing gear from extending. In other cases, brake fluid leaks through the fatigue crack resulting in loss of braking action.
Original design landing gear pivots (with the original design bushings) could crack, fail, and result in gear-up landings or loss of braking.
Cessna has issued Service Bulletin SEB90-1, Revision 3, dated March 15, 1999. The service bulletin contains procedures for:
- inspecting the main landing gear pivot assemblies for cracks,
- replacing any cracked main landing gear pivot assemblies, and
- installingnew bushings on the pivot assembly shaft.
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 Cessna Aircraft Company (Cessna) Model 172 airplanes. This proposal was published in the Federal Register as a notice of proposed rulemaking (NPRM) on October 30, 2000 (65 FR 64640). The NPRM proposed to require you to inspect the main landing gear pivot assemblies for cracks, replace any cracked main landing gear pivot assemblies, and install new bushings on the pivot assembly shaft.
What is the potential impact if FAA took no action? Original design landing gear pivots (with the original design bushings) could crack, fail, and result in gear-up landings or loss of braking.
Was the public invited to comment? The FAA encouraged interested persons to participate in the making of this amendment. The following presents the comments received on the proposaland FAA's response to each comment:
Comment Issue No. 1: Why Apply the AD Action Since it is Not Cost Effective?
What is the commenter's concern? One commenter states that this action is not cost effective because the cost of a gear up landing would be less than compliance with the AD. We infer that the commenter wants the NPRM withdrawn.
What is FAA's response to the concern? The FAA disagrees. The cost of a repair because of a gear up landing would be substantially more than compliance with the AD. The failed pivot would have to be replaced as well as repairs made for damage to the skin, antennas, propeller, wingtip, and other parts. The most important aspect is the safety issue. The passenger injuries that could be prevented through compliance with this AD outweigh the cost of compliance with this AD.
We are not changing the AD based on these comments.
Comment Issue No. 2: Why Not Apply the AD Only to Airplanes That Have Experienced Hard Landings?
Whatis the commenter's concern? Two commenters recommend that the AD only apply to airplanes that have experienced hard landings. The service bulletin recommends doing this inspection after hard landings.
What is FAA's response to the concern? We disagree. The pivot is improperly loaded during any landing because the small bushing on the pivot allows the small part of the pivot to be loaded before the main bearing is loaded. The installation of the service kit removes this problem.
We are not changing the AD based on these comments.
Comment Issue No. 3: Why Not Require the AD Only on High Time Training Airplanes Where the Landing Gear Has Experienced Many Landings?
What is the commenter's concern? Three commenters recommend that the AD only be required on high time training airplanes where the landing gear has experienced many landings.
What is FAA's response to the concern? The FAA agrees that the reported failures are probably related to the number of landingsexperienced by the pivot. However, there is no way of determining the number of landings on these airplanes and failures have happened before reaching 2,000 hours time-in-service.
We are not changing the AD based on these comments.
Comment Issue No. 4: Why Not Wait on Taking Action Until a Leak in the Brake System is Detected?
What is the commenter's concern? Two commenters state that action should not be taken unless a leak in the brake system is detected. This is because brake fluid can leak out through cracks in the pivot fitting.
What is FAA's response to the concern? The FAA disagrees. Leaking brake fluid has not preceded all reported failures. A crack would have to be nearly half way through the pivot fitting before any brake fluid would leak.
We are not changing the AD based on these comments.
Comment Issue No. 5: What is the Provision for Airplanes Already in Compliance With Cessna Service Bulletin SEB90-1, Revision 3, Dated March 15, 1999?
What is the commenter's concern? One commenter states that FAA should make a provision for airplanes already complying with the service bulletin.
What is FAA's response to the concern? The FAA agrees and we are changing the final rule AD to provide for airplanes that already meet the requirements of the service bulletin.
Comment Issue No. 6: Why Require an AD Because the Condition Rarely Results in Injury to Occupants and Airframes Are Usually Repairable?
What is the commenter's concern? Three commenters feel that an AD is not required because the condition rarely results in injury to occupants and airframes are usually repairable. Two of the commenters used the risk assessment from the Small Airplane Directorate Airworthiness Concern Process Guide to conclude that a Special Airworthiness Information Bulletin (SAIB) or General Aviation Alert (GAA) would be appropriate instead of the proposed AD. They state that a landing gear failure is not a hazardous event, and should not be considered a major or minor event when using the risk assessment.
What is FAA's response to the concern? We disagree that an SAIB or GAA would be appropriate. Although injuries in landing gear accidents involving the Cessna 172RG are rare, FAA's risk assessment shows that an airworthiness directive is required because landing gear failure is listed as hazardous in the guide.
We are not changing the final rule as a result of these comments.
FAA's Determination
What is FAA's Final Determination on this Issue? We carefully reviewed all available information related to the subject presented above and determined that air safety and the public interest require the adoption of the rule as proposed except for the changes discussed above and minor editorial corrections. These changes and corrections provide the intent that was proposed in the NPRM for correcting the unsafe condition and do not impose any additional burden than what was intended in the NPRM.
Cost Impact
How many airplanes does this AD impact? We estimate that this AD affects 766 airplanes in the U.S. registry.
What is the cost impact of this AD on owners/operators of the affected airplanes? We estimate that it would take about 20 workhours for each airplane to do both proposed pivot assembly inspections, at an average labor rate of $60 an hour. Based on the figures presented above, we estimate the total cost impact of the inspection on U.S. operators is $919,200, or $1,200 for each airplane.
We estimate that it would take about 5 workhours for each airplane, to do both bushing replacements, at an average labor rate of $60 an hour. Parts cost about $200 for each airplane. Based on the figures presented above, we estimate the total cost impact of the bushing replacement on U.S. operators is $500 for each airplane.
If a crack is found during the pivot assembly inspection, the pivot assembly must be replaced. We estimate that it would take about 3 workhours to do each pivot assembly replacement, at an average labor rate of $60 an hour. Parts cost about $2,783 for each pivot assembly. Based on the figures presented above, we estimate the total cost impact of the pivot assembly replacement on U.S. operators is $2,963 for each pivot assembly.
We have no way of knowing how many airplanes will require replacement pivot assemblies. The total cost for each airplane for this AD depends on whether a crack is found during the inspection of the pivot assembly. We estimate the total cost impact of this AD for each airplane to U.S. operators is:
Neither pivot cracked
One pivot cracked
Both pivots cracked
$1,700
$4,663
$7,626
Regulatory Impact
Does this AD impact various entities? The regulations adopted 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. We have determined that this rule does not have federalism implications under Executive Order 13132.
Does this AD involve a significant rule or regulatory action? 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. We have placed a copy of the regulatory evaluation prepared for this action in the Rules Docket. You may get a copy of it 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, 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. 39.13 [Amended]
2. FAA amends 39.13 by adding a new AD to read as follows: