[Federal Register Volume 59, Number 35 (Tuesday, February 22, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-3841]


  Federal Register / Vol. 59, No. 35 / Tuesday, February 22, 1994 /
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[[Page Unknown]]

[Federal Register: February 22, 1994]


                                                    VOL. 59, NO. 35

                                         Tuesday, February 22, 1994
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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 92-CE-38-AD; Amdt. 39-8832; AD 94-04-12]

 

Airworthiness Directives: Twin Commander Aircraft Corporation 
Models 685, 690, 690A, and 690B Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD) that 
applies to certain Twin Commander Aircraft Corporation (Twin Commander) 
Models 685, 690, 690A, and 690B airplanes. This action requires 
modifying the wing ribs at Wing Station (WS) 39, inspecting (one-time) 
WS 39 for cracks or corrosion, treating any corrosion found, and 
replacing any cracked wing front spar lower cap (spar cap). Several 
reports of cracked spar caps and cracked and deformed wing ribs at WS 
39 on the affected airplanes prompted this action. The actions 
specified by this AD are intended to prevent failure of the wing 
structure caused by a cracked spar cap or cracked or deformed wing rib 
at WS 39.

DATES: Effective April 12, 1994. The incorporation by reference of Twin 
Commander Service Bulletin (SB) No. 211, Revision 1, dated July 7, 
1992, is approved by the Director of the Federal Register as of April 
12, 1994.
    The incorporation by reference of the instructions to Twin 
Commander Custom Kit No. CK-144, Revision A, dated November 12, 1992, 
was previously approved by the Director of the Federal Register as of 
April 11, 1994.

ADDRESSES: Service information that applies to this AD may be obtained 
from the Twin Commander Aircraft Corporation, 19003 59th Drive, NE., 
Arlington, Washington 98223. This information may also be examined at 
the Federal Aviation Administration (FAA), Central Region, Office of 
the Assistant Chief Counsel, room 1558, 601 E. 12th Street, Kansas 
City, Missouri 64106, or at the Office of the Federal Register, 800 
North Capitol Street, NW., suite 700, Washington, DC.

FOR FURTHER INFORMATION CONTACT: Mr. Mike Pasion, Aerospace Engineer, 
FAA, Northwest Mountain Region, 1601 Lind Avenue SW., Renton, 
Washington 98055-4056; telephone (206) 227-2594; facsimile (206) 227-
1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations to include an AD that would apply to certain Twin 
Commander Models 685, 690, 690A, and 690B airplanes was published in 
the Federal Register on June 30, 1993 (58 FR 34959). The proposed AD 
would require (1) modifying the wing ribs at Wing Station (WS) 39; (2) 
inspecting (one-time) the main spar lower cap and lower wing stringer 
No. 7 at WS 39 for cracks or corrosion; and (3) replacing the spar cap 
if any cracks are found and treating any corrosion found. The proposed 
inspections would be accomplished in accordance with the ACCOMPLISHMENT 
INSTRUCTIONS section of Twin Commander SB No. 211, Revision 1, dated 
July 7, 1992. Replacing the spar cap, if required, would be 
accomplished in accordance with Twin Commander Custom Kit 144, Revision 
A, dated November 12, 1992; or AVIADESIGN, Inc. Supplemental Type 
Certificate SA5740NM, dated July 16, 1992, as applicable.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the 10 comments received.
    Five commenters concur with the proposal as written.
    One commenter recommends excluding Model 685 airplanes that show no 
signs of corrosion based on the inspection required by AD 91-08-09. The 
commenter feels that the proposal is unreasonably burdensome to private 
aviation (i.e., 14 CFR part 91 operators) and should not be mandatory. 
The FAA does not concur. AD 91-08-09 requires inspecting for corrosion 
on the main wing spar lower cap, but the inspection procedure will not 
detect cracks in the wing front spar lower cap (spar cap). Even if the 
inspection required by AD 91-08-09 reveals corrosion, there is no 
assurance that cracks at WS 39 do not exist. The purpose of the 
proposal is to provide a way to detect and correct cracks at WS 39. The 
FAA has determined that these cracks or failures of the WS 39 wing rib 
can occur on airplanes in any type of operation, and that this action 
is the best course to achieve the safety objective of returning the 
airplane to its original certification level of safety. The proposed AD 
is unchanged as a result of this comment.
    Another commenter, the Civil Aviation Authority of Australia (CAA), 
recommends replacing the wing spar cap before the next 500 hours time-
in-service (TIS) if corrosion is found, instead of treating any 
corrosion found. The CAA states that, if a corroded spar is not 
replaced, then the small fatigue crack formed as a result of the 
corrosion will grow to weaken the spar to a level below its design 
strength. The FAA is currently conducting a study to determine the 
fatigue crack growth rates from irregular corroded surfaces. Part of 
this study includes the consideration of a replacement time period for 
spar caps found corroded. When this study is complete, the FAA will 
consider taking further AD action to cover this issue. The proposed AD 
is unchanged as a result of this comment.
    A third commenter states that the inspection should be repetitive. 
This is one of the items the FAA is considering in the current study to 
determine the fatigue crack growth rates from irregular corroded 
surfaces. When this study is complete, the FAA will consider taking 
further AD action to cover this issue. The proposed AD is unchanged as 
a result of this comment.
    A fourth commenter requests a change in the compliance time from 50 
hours TIS to 180 days. This commenter believes that there will be a jam 
of airplanes in service shops, causing a possible parts shortage or 
forcing airplane owners/operators to utilize less qualified shops in 
order to meet the deadline. The FAA does not concur. Twin Commander has 
assured the FAA that there are adequate parts available for all repairs 
that could be required. In addition, the FAA has determined that there 
is an adequate number of certified maintenance shops available to 
accomplish the actions on all airplanes within the proposed compliance 
time. The proposed AD is unchanged as a result of this comment.
    A fifth commenter, the Twin Commander Aircraft Corporation, 
requests that the preamble of the proposal change to reflect that, of 
the 13 airplanes reported to have cracked spar caps, 12 were examined 
in detail and none had cracks exceeding the specified limits. The FAA 
concurs, and, because the entire preamble of the proposal is not 
repeated in the final rule action, the FAA is so noting this fact.
    After careful review of all available information including the 
comments referenced 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 nor add any 
additional burden upon the public than was already proposed.
    The FAA estimates that 439 airplanes in the U.S. registry will be 
affected by this AD, that it will take approximately 168 workhours per 
airplane to accomplish the required action, and that the average labor 
rate is approximately $55 an hour (total labor cost of $9,240 per 
airplane). Parts cost approximately $1,300 per airplane. Based on these 
figures, the total cost impact of this AD on U.S. operators is 
estimated to be $4,627,060 ($10,540 per airplane). As previously 
discussed, 89 of the 439 affected airplanes have already accomplished 
the required actions. This reduces the cost impact of this AD upon U.S. 
operators from $4,627,060 to $3,689,000.
    In addition, if the required inspection reveals cracks or corrosion 
that exceeds a certain amount, replacing the spar cap will be required 
at a cost of approximately $100,000 per airplane, parts and labor 
included. An airplane affected by this AD could have a compliance cost 
as low as approximately $10,540 (labor + parts) if cracks or corrosion 
is not found during the inspection, and as high as approximately 
$110,540 (inspection and modification + spar cap replacement) if the 
operator replaces the spar cap.
    Based on an expected average remaining operating life of 30 years 
per affected airplane, the annualized compliance cost would be:
     If only inspecting the spar cap and wing rib at WS 39 and 
modifying at WS 39 are necessary: $10,540  x  0.8145 (capital recovery 
factor at a 7 percent interest rate) = $858 annualized cost; or
    A If replacing the spar cap is necessary: approximately 
$110,540  x  0.8145 (capital recovery factor at a 7 percent interest 
rate) = $9,003 annualized cost.
    The required AD's from Dockets No. 92-CE-26-AD (for Model 690B and 
No. 92-CE-58AD (for Models 685, 690, 690A, and 690B) will also affect 
certain airplanes included in this AD. The compliance costs of these 
other AD's will add to the cost discussed above. However, replacing the 
spar cap will only be required once, so the $100,000 replacement cost, 
if required, is a one-time action.
    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to ensure that small entities are not unnecessarily or 
disproportionally burdened by government regulations. The RFA requires 
government agencies to determine whether rules would have a 
``significant economic impact on a substantial number of small 
entities,'' and, in cases where they would, conduct a Regulatory 
Flexibility Analysis in which alternatives to the rule are considered. 
FAA Order 2100.14A, Regulatory Flexibility Criteria and Guidance, 
outlines FAA procedures and criteria for complying with the RFA. Small 
entities are defined as small businesses and small not-for-profit 
organizations that are independently owned and operated or airports 
operated by small governmental jurisdictions.
    The 350 U.S.-registered airplanes affected by this AD that have not 
complied with Twin Commander SB No. 211, Revision 1, dated July 7, 
1992, are owned according to the following breakdown: 60 by 
individuals, 2 by U.S. government agencies, 9 by states or local 
governments, and 279 by other entities. Twenty entities own more than 
one of the affected airplanes: one owns 7, one owns 5, another owns 4, 
and the other seventeen own 2 each.
    The FAA cannot determine the sizes of all the affected non-
individual owner entities nor the relative significance of the costs 
estimated above. Because of these uncertainties, no cost thresholds for 
significant economic impact can be reasonably determined. Based on the 
possibility that this AD could have a significant impact on a 
substantial number of small entities, the FAA conducted a regulatory 
flexibility analysis. A copy of this analysis may be obtained by 
contacting the Rules Docket at the location provided under the caption 
ADDRESSES.
    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 of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this final 
rule does costs 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 significant under DOT Regulatory Policies and Procedures (44 FR 
11034, February 26, 1979) because of substantial public interest; and, 
(3) may have a significant economic impact on a substantial number of 
small entities. The FAA has conducted an Initial Regulatory Flexibility 
Determination and Analysis and has considered alternatives to this 
action that could minimize the impact on small entities. A copy of this 
analysis may be obtained by contacting the Rules Docket at the location 
provided under the caption ADDRESSES. After careful consideration, the 
FAA has determined that the required action is the best course to 
achieve the safety objective of returning the airplane to its original 
certification level of safety.

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 14 CFR part 
39 of the Federal Aviation Regulations as follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 
106(g); and 14 CFR 11.89.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new AD to read 
as follows:

94-04-12 Twin Commander Aircraft Corporation: Amendment 39-8832; 
Docket No. 92-CE-38-AD.

    Applicability: The following Model and serial number airplanes 
that do not have the wing front spar lower cap replaced in 
accordance with the procedures of one of the two specified in 
paragraph (b)(2) of this AD, certificated in any category:

------------------------------------------------------------------------
               Model                             Serial Nos.            
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685................................  12000 through 12066.               
690, 690A, and 690B................  11001 through 11566.               
------------------------------------------------------------------------

    Note 1: The serial number of the Model 685 airplanes differs 
from that specified in Twin Commander Service Bulletin (SB) No. 211, 
Revision 1, dated July 7, 1992. This AD takes precedence over that 
service information.

    Compliance: Required within the next 50 hours time-in-service 
after the effective date of this AD, unless already accomplished.
    To prevent failure of the wing structure caused by a cracked 
wing front spar lower cap or cracked or deformed wing rib at Wing 
Station (WS) 39, accomplish the following:
    (a) Modify the wing ribs at WS 39 in accordance with Part II of 
the ACCOMPLISHMENT INSTRUCTIONS section of Twin Commander SB No. 
211, Revision 1, dated July 7, 1992.
    (b) Eddy current inspect the wing front spar lower cap and lower 
wing stringer No. 7 at WS 39 for cracks or corrosion in accordance 
with Part I of the ACCOMPLISHMENT INSTRUCTIONS section of Twin 
Commander SB No. 211, Revision 1, dated July 7, 1992.
    (1) If any corrosion is found that is less than .031 inch in the 
thin flange or .063 inch in the thick section of the wing front 
lower spar cap, prior to further flight, treat the wing front spar 
lower cap area that is corroded with corrosion inhibitor such as 
LPS-3 or ACF-50.
    (2) If any cracks are found or any corrosion is found that is 
equal to or exceeds .031 inch in the thin flange or .063 inch in the 
thick section of the wing front spar lower cap, prior to further 
flight, replace the wing front spar lower cap in accordance with the 
instructions in one of the following, as applicable:
    (i) For Models 685, 690, 690A, and 690B--Twin Commander Custom 
Kit 144, Revision A, dated November 12, 1992; or
    (ii) For Models 690, 690A, and 690B--AVIADESIGN, Inc. 
Supplemental Type Certificate SA5740NM, dated July 16, 1992.
    (c) Special flight permits may be issued in accordance with 14 
CFR 21.197 and 21.199 to operate the airplane to a location where 
the requirements of this AD can be accomplished.
    (d) An alternative method of compliance or adjustment of the 
compliance time that provides an equivalent level of safety may be 
approved by the Manager, Seattle Aircraft Certification Office 
(ACO), FAA, Northwest Mountain Region, 1601 Lind Avenue SW., Renton, 
Washington 98055-4056. The request shall be forwarded through an 
appropriate FAA Maintenance Inspector, who may add comments and then 
send it to the Manager, Seattle ACO, FAA, Northwest Mountain Region.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO, FAA, Northwest Mountain Region.

    (e) The inspections required by this AD shall be done in 
accordance with Twin Commander Service Bulletin No. 211, Revision 
No. 1, dated July 7, 1992. This incorporation by reference was 
approved by the Director of the Federal Register in accordance with 
5 U.S.C. 552(a) and 1 CFR part 51. The replacement (as applicable) 
required by this AD shall be done in accordance with the 
instructions to either Twin Commander Custom Kit No. CK-144, 
Revision A, dated November 12, 1992; or Twin Commander Custom Kit 
No. CK-145, dated August 21, 1992, whichever is applicable. This 
incorporation by reference was previously approved as of April 11, 
1994 by the Director of the Federal Register in accordance with 5 
U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Twin 
Commander Aircraft Corporation, 19003 59th Drive, NE, Arlington, 
Washington 98223. Copies may be inspected at the FAA, Central 
Region, Office of the Assistant Chief Counsel, Room 1558, 601 E. 
12th Street, Kansas City, Missouri, or at the Office of the Federal 
Register, 800 North Capitol Street, NW., suite 700, Washington, DC.
    (f) This amendment (39-8832) becomes effective on April 12, 
1994.

    Issued in Kansas City, Missouri, on February 14, 1994.
Barry D. Clements,
Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. 94-3841 Filed 2-18-94; 8:45 am]
BILLING CODE 4910-13-U