[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: 94-3839]


[[Page Unknown]]

[Federal Register: February 22, 1994]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 92-CE-58-AD; Amendment 39-8834; AD 94-04-14]

 

Airworthiness Directives: Twin Commander Aircraft Corporation 
500, 680, 681, 685, and 690 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment supersedes Airworthiness Directive (AD) 91-08-
09, which currently requires the following on certain Twin Commander 
Aircraft Corporation (Twin Commander) 500, 680, 681, 685, and 690 
series airplanes: Repetitively inspecting the wing front spar lower cap 
(spar cap) for corrosion; and replacing the spar cap if corrosion 
exceeds certain limits. This action incorporates updated and more 
detailed inspection procedures, extends the repetitive inspection 
intervals, and provides the option of incorporating one of three 
modifications as terminating action for the repetitive inspections. The 
actions specified by the AD are intended to prevent wing structural 
damage that, if not detected, could progress to the point of failure.

DATES: Effective April 12, 1994. The incorporation by reference of Twin 
Commander Service Bulletin No. 208A, dated November 9, 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; 
and Twin Commander Custom Kit No. CK-145, dated August 21, 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 applies to certain Twin 
Commander Models 685, 690, 690A, and 690B airplanes was published in 
the Federal Register on June 30, 1993 (58 FR 34952). The proposed AD 
would supersede AD 91-08-09 with a new AD that would (1) retain the 
requirement of repetitively inspecting the spar cap, and replacing the 
spar cap if certain corrosion limits are exceeded; (2) incorporate Twin 
Commander SB No. 208A, dated November 9, 1992; and (3) incorporate spar 
cap replacement procedures specified in Twin Commander Custom Kit No. 
CK-144, Revision A, dated November 12, 1992; Twin Commander Custom Kit 
No. CK-145, dated August 21, 1992; and AVIADESIGN, Inc. Supplemental 
Type Certificate (STC), dated July 16, 1992.
    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.
    Seven commenters concur with the proposal as written.
    Twin Commander states that the proposal should be changed to 
reflect that Custom Kit-145, which specifies procedures for replacing 
the spar cap for certain airplanes, also affects Models 680W and 681. 
The FAA concurs and has added these models to paragraph (b)(2) of the 
proposal, and has deleted paragraph (b)(4).
    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 requests an extension of the time period for 
reinspection of a spar cap found not corroded from 36 calendar months 
to 60 calendar months. This commenter states that a well-maintained 
airplane that is always hangared and removed from a coastal environment 
should only have these inspections every 60 months. The FAA does not 
concur that this compliance time should be extended. The FAA has 
determined that the majority of airplanes affected by this proposal are 
not maintained and operated in the conditions referenced above, and 
that the 36-month inspection interval is suitable for the typical 
affected airplane when found corrosion-free. In addition, establishing 
a reliable corrosion growth rate for these airplanes is extremely 
difficult, especially considering the diverse environment and operating 
conditions these airplanes are approved for. The proposed AD is 
unchanged as a result of this comment.
    After careful review of all available information, the FAA has 
determined that air safety and the public interest require the adoption 
of the rule as proposed except for the minor change discussed above and 
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.
    Of the 562 affected airplanes registered in the United States, 10 
have already accomplished the required inspection in accordance with 
Twin Commander SB No. 208A, dated November 9, 1992. None of these 
airplanes required spar cap replacement.
    The compliance time for this AD is presented in calendar time 
instead of hours time-in-service (TIS). The FAA has determined that a 
calendar time for compliance would be the most desirable method because 
the unsafe condition described by the AD is caused by corrosion. 
Corrosion can occur on airplanes regardless of whether the airplane is 
in service.
    The FAA estimates that 562 airplanes in the U.S. registry would be 
affected by this AD, that it would take between 110 and 162 workhours 
per airplane (varies by model; a weighted average of 146 workhours) to 
accomplish the required inspection, and that the average labor rate is 
approximately $55 an hour. Based on these figures, the total initial 
cost impact of the inspection specified by this AD on U.S. operators is 
estimated to be $4,688,980 ($8,343 per airplane). As previously 
discussed, 10 of the 562 affected airplanes have already accomplished 
the required inspection. This reduces the initial cost impact of the 
inspection specified by this AD on U.S. operators to $4,432,560.
    The inspections currently required by AD 91-08-09 carry an earlier 
FAA-estimated cost impact on U.S. operators of $880 (16 workhours  x  
$55 per hour) per airplane. In actuality, those inspections range from 
$1,100 (20 workhours  x  $55 per hour) to $1,980 (36 workhours  x  $55 
per hour) depending on the airplane model. Because of the more 
comprehensive inspection procedures specified in Twin Commander SB No. 
208A, the initial cost impact of the inspections of this AD carries an 
additional cost impact of between $4,950 to $6,930 per airplane over 
that which is already required by AD 91-08-09. This AD provides owners 
of the affected airplanes some relief from some of the provisions of AD 
91-08-09. For example:
     If no corrosion is found, this AD would require repetitive 
inspections at 36-calendar month intervals instead of 12-calendar month 
intervals, which is a savings of between $2,200 to $3,960 over the next 
24 calendar months depending on the airplane model.
     If corrosion is less than 50 percent of the allowable 
service limits referenced in Twin Commander SB 208A, this AD would 
require reinspection at 30-calendar month intervals instead of 12-
calendar month intervals, which is a savings of between $2,750 to 
$4,950 over the next 30 calendar months depending on the airplane 
model.
     Replacing the spar cap terminates this repetitive 
inspection requirement, which is a savings of $1,100 to $1,980 per year 
depending on the airplane model.
    In addition, if the required inspection revealed corrosion in 
excess of certain established limits, then replacing the spar cap would 
be required at a cost of approximately $100,000, parts and labor 
included. If the spar cap did not reveal corrosion in excess of certain 
established limits, then an airplane affected by this AD could have an 
incremental compliance cost as low as $4,950 (proposed inspection cost 
at 110 workhours minus the cost of the inspection required by AD 91-08-
09) or $6,930 (required inspection cost at 162 workhours minus the cost 
of the inspection required by AD 91-08-09). If replacing the spar cap 
would be necessary, an airplane affected by this AD could have an 
incremental compliance cost as high as approximately $104,950 (required 
inspection at 110 workhours minus the cost of the inspection required 
by AD 91-08-09 plus spar cap replacement) to $106,930 (required 
inspection at 162 workhours minus the cost of the inspection required 
by AD 91-08-09 plus spar cap replacement).
    The FAA cannot predict the results of the required inspections, 
especially as the airplanes continue to age. Approximately 61 percent 
of the airplanes inspected in accordance with Twin Commander SB No. 208 
(AD 91-08-09) had no significant spar cap corrosion, 24 percent had 
less than 50 percent of the established corrosion service limits, and 
13 percent had between 50 to 100 percent of the established corrosion 
service limits. Less than 3 percent of the airplanes exceeded the 
established corrosion service limits.
    Based on an expected average remaining operating life of 20, 25, or 
30 years per affected airplane (depending on the model), the 
incremental annualized compliance cost would be:
     If only repetitively inspecting the spar cap is necessary 
for airplanes with an average operating life of 20 years: $904 to 
$7,239 incremental annualized cost (depending on the airplane model and 
frequency of inspection, and using a 7 percent interest rate);
     If only repetitively inspecting the spar cap is necessary 
for airplanes with an average operating life of 25 years: $1,195 to 
$7,176 incremental annualized cost (depending on the airplane model and 
frequency of inspection, and using a 7 percent interest rate);
     If only repetitively inspecting the spar cap is necessary 
for airplanes with an average operating life of 30 years: $1,290 to 
$7,495 incremental annualized cost (depending on the airplane model and 
frequency of inspection, and using a 7 percent interest rate);
     If replacing the spar cap is necessary for airplanes with 
an average operating life of 20 years: approximately $9,675 incremental 
annualized cost (using a 7 percent interest rate) if the spar cap is 
replaced during the first inspection;
     If replacing the spar cap is necessary for airplanes with 
an average operating life of 25 years: approximately $8,719 incremental 
annualized cost (using a 7 percent interest rate) if the spar cap is 
replaced during the first inspection; and
     If replacing the spar cap is necessary for airplanes with 
an average operating life of 30 years: approximately $8,145 incremental 
annualized cost (using a 7 percent interest rate) if the spar cap is 
replaced during the first inspection.
    The required AD's from Dockets No. 92-CE-26-AD (for Model 500S and 
690B), No. 92-CE-38-AD (for Models 685, 690, 690A, and 690B), and No. 
92-CE-43-AD (for Models 500S, 500U, 680FL, 680FL(P), 680W, and 681) 
will also affect certain airplanes included in this AD. The compliance 
costs of these other required AD's will 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 562 U.S.-registered airplanes affected by this AD are owned 
according to the following breakdown: 92 by individuals, 7 by U.S. 
government agencies, 20 by states or local governments, and 443 by 
other entities. Twenty seven entities each own more than one of the 
affected airplanes: One owns 7, four own 5 each, three own 3 each and 
nineteen 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 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 this 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 of 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 removing AD 91-08-09, Amendment 39-
6965 (56 FR 14307, April 9, 1991), and by adding the following new 
airworthiness directive to read as follows:

94-04-14 Twin Commander Aircraft Corporation: Amendment 39-8834; 
Docket No. 92-CE-58-AD. Supersedes AD 91-08-09, Amendment 39-6965.

    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 three modifications 
specified in paragraph (b) of this AD, certificated in any category:

------------------------------------------------------------------------
               Models                             Serial No.            
------------------------------------------------------------------------
500U, 680FL, 680FL(P), and 680W....  1731 through 1854.                 
500S...............................  1755 through 3323.                 
681................................  6001 through 6072.                 
685................................  12000 through 12066.               
690, 690A, and 690B................  11001 through 11566.               
------------------------------------------------------------------------

    Compliance: Required within the next 90 calendar days after the 
effective date of this AD or within 12 calendar months after the 
last inspection required by AD 91-08-09, whichever occurs later, 
unless already accomplished, and thereafter as indicated.
    To prevent wing structural damage that, if not detected, could 
progress to the point of failure, accomplish the following:

    Note 1: The serial number of the Model 685 airplanes differs 
from that specified in Twin Commander Service Bulletin (SB) No. 
208A, dated November 9, 1992. This AD takes precedence over that 
service information.

    (a) Ultrasonically inspect each area of the wing front spar 
lower cap for corrosion in accordance with the instructions in Twin 
Commander SB No. 208A, dated November 9, 1992.
    (1) If no corrosion is found, reinspect within the next 36 
calendar months.
    (2) If corrosion is found that is less than 50 percent of the 
allowable service limits referenced in Table 1 of Twin Commander SB 
No. 208A, dated November 9, 1992, reinspect within the next 30 
calendar months.
    (3) If corrosion is found to be between 50 to 100 percent of the 
allowable service limits referenced in Table 1 of Twin Commander SB 
No. 208A, dated November 9, 1992, reinspect within the next 12 
calendar months.
    (4) If corrosion is found to be greater than 100 percent of the 
allowable service limits referenced in Table 1 of Twin Commander SB 
No. 208A, dated November 9, 1992, prior to further flight, replace 
the wing front spar lower cap in accordance with one of the 
replacement modifications referenced in paragraph (b) of this AD.
    (b) The repetitive inspection requirement of this AD may be 
eliminated by replacing the wing front lower spar cap in accordance 
with the instructions in one of the following, as applicable:
    (1) For Models 685, 690, 690A, and 690B: Twin Commander Custom 
Kit No. CK-144, Revision A, dated November 12, 1992;
    (2) For Models 500S, 500U, 680W, 681, 680FL, and 680FL(P): Twin 
Commander Custom Kit No. CK-145, dated November 21, 1992; or
    (3) For Models 690, 690A, and 690B: AVIADESIGN, Inc. 
Supplemental Type Certificate SA5740NM.
    (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 
initial and repetitive compliance times 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. 208A, dated 
November 9, 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 by the Director of the Federal 
Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51 as of 
April 11, 1994. 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 (39-8834) supersedes AD 91-08-09, Amendment 
39-6965.
    (g) This amendment (39-8834) 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. 94-3839 Filed 2-18-94; 8:45 am]
BILLING CODE 4910-13-U