[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: 94-3840]


[[Page Unknown]]

[Federal Register: February 22, 1994]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 92-CE-57-AD; Amdt 39-8835; AD 94-04-15]

 

Airworthiness Directives: Twin Commander Aircraft Corporation 
Models 500, 560A, 560E, 680, 680E, and 720 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 500, 560A, 560E, 680, 680E, and 720 airplanes. This action 
requires inspecting the wing front spar lower cap (spar cap) for 
interference, fretting, or corrosion between the firewall flange and 
spar cap flange at Wing Station (WS) 96, and clearing any interference, 
repairing any fretting or corrosion damage, and replacing any cracked 
spar cap. Reports of two of the affected airplanes have cracked spar 
caps at WS 96 prompted this action. The actions specified by this AD 
are intended to prevent failure of the wing structure caused by a 
cracked spar cap at WS 96.

DATES: Effective April 12, 1994. The incorporation by reference of 
certain documents listed in the regulations is approved by the Director 
of the Federal Register as of April 12, 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) 
277-2594; facsimile (206) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations to include an AD that applies to certain Twin 
Commander Models 500, 560A, 560E, 680, 680E, and 720 airplanes was 
published in the Federal Register on June 30, 1993 (58 FR 34950). The 
action proposed to require inspecting the spar cap for interference, 
fretting, or corrosion between the firewall flange and spar cap flange 
at WS 96, and clearing any interference, repairing any fretting or 
corrosion damage, and replacing any cracked spar cap. The proposed 
inspection and repair, if applicable, would be accomplished in 
accordance with Twin Commander SB No. 212, dated November 3, 1992.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the nine comments received.
    Seven commenters concur with the proposal as written.
    One commenter, the Civil Aviation Authority of Australia (CAA), 
states that the proposal should require an eddy current inspection of 
the spar cap. The CAA questions whether fretting and corrosion are the 
sole contributors to fatigue damage to WS 96, or if these merely 
aggravate what is already a fatigue-sensitive location. The CAA goes on 
to state that, if a crack can start from a corrosion pit as small as 
0.006 inches (as happened on a Swedish airplane), then there is a good 
chance that even a clean airplane will crack over time. Also, the CAA 
states that, if a fatigue crack has started at the base of a corrosion 
pit, the blending of the corrosion will smear over the crack and 
conceal it from the dye penetrant inspection (which is called for in 
the SB), and that an eddy current inspection is the only method for 
detection of this crack. The FAA does not concur. The proposal relates 
to fretting that may occur because interference between a firewall 
stiffener and the forward flange of the lower spar cap. It would 
require action for fatigue cracks found as a result of this 
interference and fretting. Fretting does have a synergistic 
relationship with corrosion and fatigue, and its existence greatly 
accelerates fatigue crack growth. The FAA has received no reports of 
fatigue cracks in the affected area that were not a direct result of 
fretting. Also, the spar cap at WS 96 is extremely difficult to inspect 
using eddy current methods because of other structures in the area 
interfering with placement of the eddy current probe. Dye penetrant 
inspections are used extensively in the aviation industry and have 
proved very reliable in detecting cracks. The proposed AD is unchanged 
as a result of this comment.
    Another commenter, the Twin Commander Aircraft Corporation states 
that owners/operators should have their airplanes inspected regardless 
of whether the spar cap has been replaced because interference may even 
exist on a new spar. The FAA concurs that interference may exist if a 
new spar is installed, unless it was installed in accordance with 
replacement procedures obtained from the manufacturer through the 
Manager, Seattle Aircraft Certification Office (as specified in 
paragraph (a)(3) of the proposed AD). The Seattle Aircraft 
Certification Office has not issued any of these procedures to airplane 
owners/operators; therefore, no airplane has the spar cap replaced in 
accordance with paragraph (a)(3) of the proposal and the proposal would 
affect all of the airplanes listed under the Applicability section. The 
proposed AD is unchanged as a result of this comment.
    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 332 airplanes in the U.S. registry will be 
affected by the proposed AD, that it will take approximately 20 
workhours per airplane to accomplish the required inspection, and that 
the average labor rate is approximately $55 an hour. Parts to 
accomplish the required inspection cost approximately $20. Based on 
these figures, the total cost impact of the inspection specified in 
this AD on U.S. operators is estimated to be $371,840. One airplane 
owner has already accomplished the required inspection, and found no 
damage or cracks.
    In addition, if the required inspection reveals cracks, or 
corrosion that exceeds certain limits, replacing the spar cap would be 
required at a cost of approximately $100,000, parts and labor included. 
An airplane affected by this AD could have a compliance cost as low as 
approximately $1,120 (labor + parts) if no cracks, interference, or 
corrosion damage is found during the inspection, and as high as 
approximately $101,120 (inspection + spar cap replacement) if the 
operator replaces the spar cap.
    Based on these airplanes having an expected average remaining 
operating life of 10 years or 15 years, the annualized compliance cost 
would range between:
     If only inspecting the spar cap at WS 96 is necessary for 
airplanes with an average remaining operating life of 10 years: 
$1,120 x 0.14349 (10-year capital recovery factor at a 7 percent 
interest rate)=$168 annualized cost;
     If only inspecting the spar cap at WS 96 is necessary for 
airplanes with an average remaining operating life of 15 years: 
$1,120 x 0.11434 (15-year capital recovery factor at a 7 percent 
interest rate)=$126;
     If replacing the spar cap is necessary for airplanes with 
an average remaining operating life of 10 years: approximately 
$101,120 x 0.15349 (capital recovery factor at a 7 percent interest 
rate)=$15,520; or
     If replacing the spar cap is necessary for airplanes with 
an average remaining operating life of 15 years: approximately 
$101,120 x 0.11434 (capital recovery factor at a 7 percent interest 
rate)=$11,562.
    The required AD's from Dockets No. 92-CE-43-AD (for Models 500, 
560A, 560E, 680, 680E, and 720) and No. 92-CE-58-AD (for Models 685, 
690, 690A, and 690B) will also affect certain airplanes included in 
this AD. The compliance costs of these other required AD's would add to 
the cost discussed above. However, replacing the spar cap would only be 
required once, so the $100,000 replacement cost, if required, would be 
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 331 U.S.-registered airplanes affected by the required AD that 
have not complied with Twin Commander SB No. 212, dated November 3, 
1992, are owned according to the following breakdown: 196 by 
individuals, 2 by U.S. government agencies, 7 by states or local 
governments, and 126 by other entities. Six entities own 2 airplanes 
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 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:

94-04-15 Twin Commander Aircraft Corporation: Amendment 39-8835; 
Docket No. 92-CE-57-AD.

    Applicability: The following model and serial number airplanes 
that do not have the wing front spar lower cap replaced in 
accordance with procedures specified in paragraph (a)(3) of this AD, 
certificated in any category:

------------------------------------------------------------------------
              Model                              Serial No.             
------------------------------------------------------------------------
500..............................  618 through 750.                     
560A.............................  231 through 450.                     
560E.............................  433 through 750.                     
680..............................  242 through 658.                     
680E.............................  623 through 750.                     
720..............................  501 through 750.                     
------------------------------------------------------------------------

    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 at Wing Station (WS) 96, accomplish the 
following:
    (a) Inspect the wing front spar lower cap of each wing for 
corrosion or interference between the firewall flange and spar 
flange in accordance with the ACCOMPLISHMENT INSTRUCTIONS section of 
Twin Commander Service Bulletin (SB) No. 212, dated November 3, 
1992.
    (1) If any interference is found between the firewall flange and 
spar flange, prior to further flight, clear this interference in 
accordance with the ACCOMPLISHMENT INSTRUCTIONS section of Twin 
Commander SB No. 212, dated November 3, 1992.
    (2) If any corrosion damage is found, prior to further flight, 
repair any corrosion damage to the wing front spar lower cap in 
accordance with the ACCOMPLISHMENT INSTRUCTIONS section of Twin 
Commander SB No. 212, dated November 3, 1992.
    (3) If any cracks are found, prior to the further flight, 
replace the wing front spar lower cap in accordance with replacement 
procedures obtained from the manufacturer through the Manager, 
Seattle Aircraft Certification Office (ACO), at the address 
specified in paragraph (c) of this AD.
    (b) 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.
    (c) 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 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: 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.

    (d) The inspection and repair required by this AD shall be done 
in accordance with Twin Commander Service Bulletin No. 212, dated 
November 3, 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. 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.
    (e) This amendment (39-8835) 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. 94-3840 Filed 2-18-94; 8:45 am]
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