What Events Have Caused This AD?
Initial AD Action
Reports of fatigue cracks of the wing spar lower cap areas caused FAA to issue AD 79-10-15, Amendment 39-3711 against Cessna Models 401, 401A, 401B, 402, 402A, 402B, 411, and 411A airplanes. AD 79-10-15 currently requires repetitive inspections of the right and left wing spar lower cap areas for fatigue cracks and wing spar cap repair or replacement as necessary.
Accomplishment of the actions mandated by AD 79-10-15 currently requires following Cessna Service Bulletin ME79-16, Revision 3, dated February 8, 1980.
AD 79-10-15 allows for the incorporation of Cessna Service Kit SK402-36 or SK411-56 on the front wing spar lower cap as terminating action for the repetitive inspections on the applicable wing.
In addition to AD 79-10-15, FAA issued AD 99-11-13 (64 FR 29781, June 3, 1999), requiring inspections of the forward, aft, and auxiliary wing spars for cracks on Cessna Models 402C airplanes with repair or replacement as necessary. AD 99-11-13 also required the operator to report the results of the inspections to FAA. AD 99-11-13 resulted from an accident where the right wing of a Cessna 402C failed just inboard of the nacelle at Wing Station (WS) 87. Investigation revealed fatigue cracking of the forward main spar that initiated at the edge of the front spar forward lower spar cap. FAA determined the spar cap cracking could continue to develop over the life of the affected airplanes and issued AD 2000-23-01, Amendment 39-11971 (65 FR 70645, November 27, 2000), to require repetitive inspections of the forward, aft, and auxiliary wing spars for cracks on Cessna Models 402C airplanes with repair or replacement as necessary. The Model 402C airplanes have a similar type design to that of the Models 401, 401A, 401B, 402, 402A, 402B, 411, 411A, and 414A airplanes.
Wing Analysis
Cessna analyzed the wing, including fatigue and crack growth analyses, on the affected airplanes. Analysis included:
--A determination of the probable location and modes of damage based on analytical results, available test data, and service information;
--Classical fatigue analyses;
--Crack growth and residual strength analyses including use of linear elastic fracture mechanics methods; --Full-scale ground testing to validate analytical models; and
--A flight strain survey to develop stress spectra used in the analyses.
The inspections required by AD 79-10-15 following Cessna Service Bulletin ME79-16, Revision 3, use a nondestructive inspection (NDI) surface eddy current method.
Based on the analysis, Cessna found that the eddy current method will not find the crack until it is .03 inch longer than the critical crack length. When the crack reaches the critical length, it is not reliably detectable because it is under the head of the fastener. Once the main spar cap is severed, the remaining structure will no longer meet the residual strength requirements. Wing separation could then occur under loading conditions less than those established for the design limit load.
Cessna reported only one instance where use of the NDI eddy current procedure detected cracks. There are other reported instances where cracks were detected visually on the aft flange in the wheel well area. The access doubler flanges cover a large percentage of the forward spar flange, hampering the effectiveness of visual inspections.
To meet industry NDI standards, cracks need to be found on Cessna Models 401, 401A, 401B, 402, 402A, 402B, 411, and 411A airplanes through NDI inspection methods with a 90-percent probability of detection at a 95-percent confidence level.
Cessna's analysis indicates the probability and confidence levels are not being met. The FAA concurs.
Action Based on Cessna's Analysis
We issued proposals to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include two ADs that would apply to Cessna Models 401, 401A, 401B, 402, 402A, 402B, 402C, 411, 411A, and 414A airplanes. The proposals (Docket Nos. 2002-CE-05-AD and 2002-CE- 57-AD) published in the Federal Register as notices of proposed rulemaking (NPRMs) on May 15, 2003 (68 FR 26239 and 68 FR 26244). The NPRMs proposed the following:
Docket No. 2002-CE-05-AD: applied to Cessna Models 401, 401A, 401B, 402, 402A, 402B, 411, and 411A airplanes and proposed to supersede AD 79-10-15 with a new AD that would require one of the following (depending on the aircraft configuration):
PFor airplanes that do not incorporate one of the specified Cessna Service Kits: Repetitively inspect the wing spar caps for fatigue cracks and repair or replace the wing spar caps as necessary and incorporate a spar strap modification on each wing spar; or
PFor airplanes that incorporate one of the specified Cessna Service Kits: Repetitively inspect the wing spar caps and straps for fatigue cracks and repair or replace the wing spar caps and straps as necessary.
Docket No. 2002-CE-57-AD: applied to Cessna Models 402C and 414A airplanes and proposed to supersede AD 2000-23-01 with a new AD that would require you to:
PInspect the wing spar caps for fatigue cracks;
PRepair or replace the wing spar caps as necessary; and
PIncorporate a spar strap modification on each wing spar.
The FAA invited interested persons to participate in the development of these amendments during the original 75-day comment periods. We extended the comment periods for another 30 days and then reopened the comment periods for another 60 days. We received numerous comments on the NPRMs.
In addition, FAA held two public meetings: One on March 3 and 4, 2004, in Herndon, Virginia, and another on August 18, 2004, in Kansas City, Missouri. The public meetings allowed an open flow of communication among FAA, the public, and industry on issues related to the NPRMs.
After analyzing all information related to this subject, FAA decided not to issue the ADs as proposed, and that the best way to address the unsafe condition is for FAA, the public, and industry to develop alternative solutions to address the unsafe condition.
Therefore, FAA withdrew the two NPRMs and gathered the necessary information to address the situation. That information led to FAA's determination, at that time, to initiate AD action against the Models 401, 401A, 401B, 402, 402A, 402B, 411, and 411A airplanes; and not against the Models 402C and 414A airplanes. The plan was to address the action through the regular rulemaking process with a notice of proposed rulemaking.
Most Recent Service History
In 2005, the FAA received reports of (and analyzed data from) cracks found in the wings of two Cessna Model 402C airplanes. The Model 402C airplanes have a similar type design to that of the Models 401, 401A, 401B, 402, 402A, 402B, 411, 411A, and 414A airplanes.
On the first airplane, information indicated the airplane had severe cracking on its left wing in the vicinity of the forward spar and outboard engine beam. The main lower spar cap had completely failed at about WS 114. The airplane had cracks in the lower wing skin and the web splice doubler. Also found were two popped rivets: One
between the heat shield and the wing skin and another between the factory installed web splice doublers and web. The airplane had 20,355 total hours time-in-service (TIS).
During the airplane's most recent flights before the cracking was found, the pilot noticed that roll trim was required. The flights required the pilot to use aileron trim to maintain level flight. The airplane landed safely and inspection revealed the cracks.
On the second airplane, fatigue cracks were found at about WS 114 in the main lower spar cap of another Model 402C airplane that had over 20,000 total hours TIS. Fatigue analysis shows that similar fatigue cracks could also develop in the wings of the Model 414A airplanes.
Logbook records indicated that both airplanes with cracked spars were in compliance with AD 2000-23-01. The FAA received a third report of another cracked spar found at WS 114 on one of the two Model 402C incident airplanes.
Therefore, FAA issued Emergency AD 2005-05-51 to detect and correct cracking in the wing spars of the Cessna Models 402C and 414A airplanes before the cracks could grow to failure. Such a wing failure could result in the wing separating from the airplane with consequent loss of control of the airplane.
Emergency AD 2005-05-51 superseded AD 2000-23-01 and:
Required the visual inspections of the forward, aft, and auxiliary wing spars for cracks more frequently on Model 402C airplanes including special emphasis areas;
Added inspection requirements for the Model 414A airplanes; and
Included provisions to position the airplane to a home base, hangar, maintenance facility, etc.
Emergency AD 2005-05-51 did not affect those airplanes that incorporated a spar strap modification on each wing following the original release of (or a later FAA-approved revision to) Cessna Service Bulletin MEB02-5 and Cessna Service Kit SK402-47 (currently at MEB02-5 Revision 2 and SK402-47B).
Long-Term Continued Operational Safety
Emergency AD 2005-05-51 was considered an interim action to immediately require visual inspection of the forward, aft, and auxiliary wing spars for cracks. The intent was to immediately detect existing cracking before it grew to wing failure.
Cessna developed inspection techniques (eddy current) for the forward spar that are more effective at detecting cracks before the structural integrity of the wing is compromised. These inspection techniques allow for longer intervals between repetitive inspections than in emergency AD 2005-05-51. Based on this, FAA issued AD 2005-05- 52, Amendment 39-14022 (70 FR 13362, dated March 21, 2005). The inspection techniques addressed by AD 2005-05-52 for the Cessna Models 402C and 414A airplanes are similar to those required by AD 79-10-15 for the Models 401, 401A, 401B, 402, 402A, 402B, 411, and 411A airplanes.
However, based on the analysis and recent service history, the FAA has determined that the long-term operational safety of the Cessna airplanes addressed by both AD 2005-05-52 and AD 79-10-15 can only be assured through the incorporation of a spar strap modification and long-term repetitive inspections. Since Models 402, 401A, 401B, 402, 402A, 402B, 411, and 411A have a similar type design to that of Models 402C and 414A airplanes, FAA is also issuing AD 2005-12-13 to require the spar strap modification and long-term inspections on those airplanes.
What is the potential impact if FAA took no action? Wing spar cap failure caused by undetected fatigue cracks could result in loss of a wing with consequent loss of airplane control.
Is there service information that applies to this subject? Cessna has issued the following:
--Original issue dated September 24, 2001, and Revision 1, dated December 22, 2003, of both Cessna Multi-engine Service Bulletin MEB01- 06 and Service Kit SK402-46A; and
--Original issue dated September 24, 2001, of both Cessna Multi-engine Service Bulletin MEB01-07 and Service Kit SK411-59.
This service information includes procedures for inspecting lower wing spar caps and incorporating a spar strap modification.
FAA's Determination and Requirements of the AD
What has FAA decided? We have evaluated all pertinent information and identified an unsafe condition that is likely to exist or develop on other products of this same type design.
Since the unsafe condition described previously is likely to exist or develop on other Cessna Aircraft Company Models 401, 401A, 401B, 402, 402A, 402B, 411, and 411A airplanes of the same type design, we are issuing this AD to detect and correct wing spar cap failure caused by undetected fatigue cracks. Such failure could result in loss of a wing with consequent loss of airplane control.
What does this AD require? This AD supersedes AD 79-10-15 with a new AD that incorporates the actions in the previously referenced service bulletins.
Why do the compliance times of this AD range between 100 hours TIS and 800 hours TIS? We have established the compliance times based on risk analysis that also allows for compliance scheduling. Some of these airplanes utilize "for hire" operations and could accumulate as many as 200 hours TIS in a month. The compliance time range is based on total hours TIS, which will address those high-usage airplanes first.
We are issuing this AD as a final rule; request for comments instead of a notice of proposed rulemaking (NPRM). We have evaluated comments from the previous AD actions on this subject and the two public meetings as well as the incidents that have occurred since (e.g., the actions of Emergency AD 2005-05-52). Based on this, FAA has determined that addressing the unsafe condition with public comment prior to issuing this AD action is impracticable. The FAA will evaluate any new comments received and amend the AD as necessary.
How does the revision to 14 CFR part 39 affect this AD? On July 10, 2002, we published a new version of 14 CFR part 39 (67 FR 47997, July 22, 2002), which governs 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.
Comments Invited
Will I have the opportunity to comment before you issue the rule? This AD is a final rule that involves requirements affecting flight safety and was not preceded by notice and an opportunity for public comment; however, we invite you to submit any written relevant data, views, or arguments regarding this AD. Send your comments to an address listed underADDRESSES. Include "Docket No. FAA-05-21176; Directorate Identifier 2005-CE-25-AD" in the subject line of your comments. If you want us to acknowledge receipt of your mailed comments, send us a self- addressed, stamped postcard with the docket number written on it; we will date-stamp your postcard and mail it back to you. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify it. If a person contacts us through a nonwritten communication, and that contact relates to a substantive part of this AD, we will summarize the contact and place the summary in the docket. We will consider all comments received by the closing date and may amend the AD in light of those comments.
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 106describes 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 the scope 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 "AD Docket FAA-05-21176; Directorate Identifier 2005-CE-25-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. The FAA amends Sec. 39.13 by removing Airworthiness Directive (AD) 79-10-15, Amendment 39-3711, and by adding a new AD to read as follows: