Discussion
What prior AD action did FAA take on this subject? In 1980, FAA issued AD 80-26-05, Amendment 39-3994, in order to detect and correct cracked main landing gear (MLG) inboard door hinge assemblies on certain Piper PA-31 series airplanes. AD 80-26-05 currently requires you to repetitively inspect the MLG inboard door hinges and attachment angles for cracks; and requires you to replace any cracked MLG inboard door hinge or attachment angle.
On December 1, 1995, 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 Piper PA-31 series airplanes. This proposal was published in the Federal Register as a notice of proposed rulemaking (NPRM) on December 7, 1995 (60 FR 62774), and proposed to supersede AD 80-26-05, Amendment 39-3994.
The NPRM proposed to:
- retain the requirement of repetitively inspecting the MLG inboard door hinge assemblies for cracks, and replacing any cracked MLG inboard door hinge assembly; and
- require incorporating a MLG inboard door hinge assembly of improved design (part number (P/N) 47529-32) or FAA-approved equivalent part number, as terminating action for the repetitive inspection requirement.
Accomplishment of the proposed inspections would have been required in accordance with Piper Service Bulletin (SB) No. 682, dated July 24, 1980.
This NPRM was consistent with FAA's aging commuter-class aircraft policy, which briefly states that, when a modification exists that could eliminate or reduce the number of required critical inspections, the modification should be incorporated. This policy is based on FAA's determination that reliance on critical repetitive inspections on aging commuter-class airplanes carries an unnecessary safety risk when a design change exists that could eliminate or, in certain instances, reduce the number of those critical inspections. The alternative to installing the improved design hinge assemblies on the affected airplanes would be to rely on the repetitive inspections required by AD 80-26-05 to detect cracks in these areas.
Was the public invited to comment on the NPRM? The FAA invited interested persons to participate in the making of this amendment. Due consideration was given to the one comment received.
What issue did this comment address? The comment received on the NPRM contained information that the improved design MLG inboard door hinge assemblies, P/N 47529-32, are also susceptible to fatigue cracking, and that installing this assembly should not eliminate the need for the repetitive inspections currently required by AD 80-26-05. The commenter stated that its airplane fleet has experienced three failures and three incidents related to fatigue cracking of the P/N 47529-32 hinge assemblies.
What action did FAA take? We conducted a review of the manufacturer's service history and service difficulty reports in FAA's database associated with the P/N 47529-32 MLG inboard door hinge assembly. Based on a review of this information, including the information received from the commenter, we determined that more information and analysis were needed before mandating MLG inboard door hinge assembly replacements through an AD.
We then issued an advance notice of proposed rulemaking (ANPRM) on February 11, 1997. The ANPRM was published in the Federal Register on February 19, 1997 (62 FR 7375). The purpose of the ANPRM was to encourage interested persons to provide information that describes what they consider the best action (if any) for FAA to take regarding the P/N 47529-32 MLG inboard door hinge assembly issue. The FAA also withdrew the NPRM. We received no information or comments regarding the ANPRM.
We then re-evaluated the information in our service difficulty database. The database, at that time, contained 10 reports of failure or cracks found in the MLG inboard door hinge assembly on the affected airplanes. The commenter to the original NPRM had submitted six of these reports. Three of these six incident reports were specifically attributed to the original MLG inboard door hinge assemblies and three to the improved design MLG inboard door hinge assemblies. The four reports that others submitted do not specifically identify whether the original MLG inboard door hinge assemblies were installed or the improved design assemblies were installed. Since the incidents occurred on high service time airplanes and since there is no AD action mandating the installation of the improved-design MLG inboard door hinge assemblies, we presumed that the original hinge assemblies were installed.
The FAA then reviewed the three incident reports on the improved design MLG inboard door hinge assemblies and, along with the National Transportation Safety Board (NTSB), performed extensive testing and analysis of the improved design MLG inboard door hinge assemblies. Based on this review, testing,and analysis, we determined that:
- the incidents were isolated and that mandating repetitive inspections was not needed when the P/N 47529-32 MLG inboard door hinge assemblies are installed; and
- AD action should be taken to eliminate the repetitive short-interval inspections that AD 80-26-05 requires and to prevent separation of a MLG door from the airplane caused by a cracked inboard door hinge assembly.
On October 14, 1997, FAA issued an NPRM to address these issues. The NPRM was published in the Federal Register on October 21, 1997 (62 FR 54595).
What has happened to justify this AD action? Since issuance of the NPRM, we have received additional reports of cracks in the MLG inboard door hinge assemblies. The reports reference incidents on both the original design assemblies and the improved design hinges. As of the issue date of this document, we have reports of the following:
- 27 reports of cracked improved design MLG inboard door hinge assemblies; and- 41 reports of cracked original design MLG inboard door hinge assemblies.
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 Piper PA-31 series airplanes. This proposal was published in the Federal Register as a supplemental NPRM on July 21, 2000 (65 FR 45323). The supplemental NPRM proposed to supersede AD 80-26-05, Amendment 39-3994, with a new AD that proposed to require:
- repetitively inspecting the MLG inboard door hinge assemblies (regardless of part number); and
- immediately replacing any cracked MLG inboard door hinge assembly with a new MLG inboard door hinge assembly, Piper part number (P/N) 47529-32 (or FAA-approved equivalent part number).
What is the potential impact if FAA took no action? These actions are necessary to detect and correct cracked MLG inboard door hinge assemblies. These cracked door hinge assemblies could result in the MLG becoming jammed with consequent loss of control of the airplane during landing operations.
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 proposal and FAA's response to each comment:
Comment Issue No. 1: Piper Part Number (P/N) 47529-32 MLG Door Hinge Assemblies Are Not Made of Steel
What is the commenter's concern? The commenter states that the NPRM incorrectly identifies the Piper P/N 47529-32 MLG door hinge assemblies as parts made of steel. The commenter explains that these assemblies are made of aluminum.
What is FAA s response to the concern? We concur that the Piper P/N 47529-32 MLG door hinge assemblies are made of aluminum. We inadvertently referenced these parts as steel parts in the supplemental NPRM.
We are changing the final rule AD accordingly.
Comment Issue No. 2: All MLG Door Hinge Assemblies Should be Inspected at 100-Hour TIS Intervals
What is the commenter's concern? The commenter expresses doubt that the Piper P/N 47529-32 MLG door hinge assemblies can go as long as 2,000-hour TIS intervals between inspections before cracking. The commenter recommends 100-hour TIS interval inspections for these assemblies.
What is FAA s response to the concern? We determined that the 2,000-hour TIS interval was an adequate compliance time for these parts based on our conservative estimate of all quantitative information available. The service reports indicate failures on airplanes ranging from a low of 3,615 total hours TIS to a high of 14,852 total hours TIS.
We are not changing the final rule AD as a result of this comment.
Comment Issue No. 3: FAA Underestimated the Cost Impact
What is the commenter's concern? The commenter states that the cost impact presented in the supplemental NPRM is incorrect because:
- removal of the hinges provides the most practical method of fluorescent dye-penetrant inspections and this would raise the inspections costs from $120 to $500; and
- the cost of Piper P/N 47-528-32 MLG door hinge assemblies is approximately $465 instead of $270 as specified in the supplemental NPRM.
What is FAA s response to the concern? We do not concur with changing the cost to accomplish the inspection. While removing the hinges from the airplane to accomplish the inspection is an option, FAA has determined that you can adequately accomplish the inspections without removing the hinges.
After checking with the manufacturer, we concur that the cost for the replacement MLG door hinge assemblies is approximately $465.
We are changing the Cost Impact section of this document accordingly.
Comment Issue No. 4: AD Should Not Apply to MLG Door Hinge Assemblies That Are Made of Steel
What is the commenter's concern? The commenter states that the AD should follow Piper Service Bulletin No. 682 and not require inspections on airplanes that have MLG door hinge assemblies that are made of steel. The commenter also requests that FAA include a list of the two outside sources that currently provide assemblies made of steel.
What is FAA s response to the concern? We concur that the AD should not apply to MLG door hinge assemblies that are made of steel and we are changing the final rule accordingly.
However, FAA is not including the list of those outside sources that currently provide assemblies made of steel. If we did include this list, out of fairness, we would feel obligated to revise the AD anytime an outside source developed and received approval for installation of MLG door hinge assemblies made of steel on the affected airplanes.
A list of outside vendors with FAA-approved assemblies made of steel is always available from the FAA address included in the AD.
The FAA's Determination
What is FAA's final determination on this issue? We carefully reviewed all available information related to the subject presented above anddetermined that air safety and the public interest require the adoption of the rule as proposed except for the changes discussed above and editorial corrections. These changes and corrections provide the intent that was proposed in the supplemental NPRM for correcting the unsafe condition and do not impose any additional burden than what was intended in the supplemental NPRM.
Cost Impact
How many airplanes does this AD impact? We estimate that this AD affects 2,344 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 accomplish the initial inspection:
Labor Cost
Parts Cost
Total Cost Per Airplane
Total Cost on U.S. Airplane Operators
2 workhours X $60 per hour = $120.
No parts required for the inspection.
$120 per airplane.
$281,280.
We estimate the following costs to accomplish the replacement, if necessary:
Labor Cost
Parts Cost
Total Cost Per Airplane
2workhours X $60 per hour = $120.
$465 per airplane.
$585 per airplane.
Regulatory Impact
Does this AD impact various entities? The regulations adopted herein 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. Therefore, it is determined that this final 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. A copy of thefinal 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, 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 removing Airworthiness Directive (AD) 80-26-05, Amendment 39-3994, and by adding a new AD to read as follows: