[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: 94-3842]


[[Page Unknown]]

[Federal Register: February 22, 1994]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 92-CE-26-AD; Amdt. 39-8831; AD 94-04-11]

 

Airworthiness Directives: Twin Commander Aircraft Corporation 
Models 500S 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 500S and 690B airplanes. This action requires removing a sample 
of the wing front spar lower cap (spar cap) material for examination, 
and, depending upon the results of that examination, inspecting or 
replacing the spar cap. Reports of cracks caused by stress corrosion in 
the spar cap on several of the affected airplanes prompted this action. 
The actions specified by this AD are intended to prevent failure of the 
wing structure caused by cracks in the spar cap.

DATES: Effective April 11, 1994. The incorporation by reference of 
certain documents in the regulations is 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 500S and 690B airplanes was published in the Federal 
Register on June 30, 1993 (58 FR 34957). The action proposed to require 
removing a sample of the spar cap material for examination, and, 
depending upon the results of the examination, inspecting or replacing 
the spar cap. The proposed inspections would be accomplished in 
accordance with Twin Commander SB No. 215, dated March 3, 1992. The 
proposed replacements, if necessary, would be accomplished in 
accordance with one of the following, as applicable:
     Twin Commander Custom Kit No. CK-144, Revision A, dated 
November 12, 1992, which applies to Twin Commander Model 690B 
airplanes;
     Twin Commander Custom Kit No. CK-145, dated August 21, 
1992, which applies to Twin Commander Model 500S airplanes; or
     AVIADESIGN, Inc. Supplemental Type Certificate (STC), 
dated July 16, 1992, which applies to Twin Commander Model 690B 
airplanes.
    Of the 80 affected airplanes registered in the United States, 34 
have already accomplished this inspection in accordance with Twin 
Commander SB No. 215, dated March 3, 1992. For five of these airplanes, 
or approximately 15 percent, the examination revealed a grain structure 
that would require spar cap replacement under the criteria of this 
proposed AD. These five airplane operators voluntarily replaced the 
spar cap in order to assure safety of their airplane.
    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.
    Eight commenters concur with the proposed rule as written.
    One commenter recommends deleting the terms ``fine equi-axed'' and 
``unusual cap grain structure'' from the proposal. This commenter 
states that there is no standard for grain structure in aluminum alloy 
products and believes that characterizing the spar cap grain structure 
as unusual is inappropriate and may not focus on the best course of 
corrective action. The Commenter also states that the word fine in 
``fine equi-axed grain structure'' is so imprecise that the structure 
is unable to be accurately measured. The FAA concurs that ``unusual 
grain structure'' could be inappropriate and has changed the wording in 
the final rule AD to ``smaller than the large elongated grains, but not 
fine equi-axed''. The FAA does not concur that the term ``fine equi-
axed'' is imprecise because the FAA included in the proposal (Note 2) a 
definition of this term. In addition, the EMTEC Corporation, which is 
the laboratory conducting the metallurgical examinations, has 
established, with the FAA and Twin Commander, the acceptable grain 
structure size of the spar cap.
    This commenter also states that the grain structure should not be 
the sole indicator of susceptibility to stress corrosion. The FAA 
concurs. The affected airplanes are also included in the applicability 
of the actions specified in Dockets No. 92-CE-38-AD and No. 92-CE-43-
AD, which require other inspections of the spar cap. The proposed AD is 
unchanged as a result of this comment.
    The same commenter also recommends consideration of other 
comprehensive corrective actions that deal with the impact of design 
and operating stress and sources of bi-metallic-initiated general 
corrosion. The FAA has determined that the current corrective action is 
one that will return the airplane to its original certification level 
of safety. The FAA will evaluate any detailed corrective action, and, 
if determined to provide an equivalent level of safety, will approve it 
as an alternative method of compliance to that portion of the required 
action. The proposed AD is unchanged as a result of this comment.
    Another commenter, the Civil Aviation Authority of Australia (CAA), 
recommends that the FAA expand the range of serial numbers in the 
applicability and expand the spar cap replacement to include all 
unusual grain structures as well as fine equi-axed grain structures. 
The FAA has re-examined all information related to this subject and has 
determined that the airplanes manufactured with spars of the fine equi-
axed grain structure are limited to those manufactured between May 1978 
and October 1979. The results of inspections received to date including 
those from the CAA verify this conclusion. The proposed AD is unchanged 
as a result of this comment.
    After examining 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 the 
minor wording change 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.
    The FAA estimates that 80 airplanes in the U.S. registry will be 
affected by this AD, that it will take approximately 15 workhours per 
airplane to accomplish the required action, and that the average labor 
rate is approximately $55 an hour. Parts cost approximately $32 per 
airplane, and the metallurgical inspection will cost approximately 
$150. Based on these figures, the total cost impact of this AD on U.S. 
operators is estimated to be $81,360. As previously discussed, 34 of 
the 80 affected airplanes have already accomplished the required 
actions. This reduces the cost impact of this AD upon U.S. operators to 
$56,392. The manufacturer will also incur the cost of the required 
metallurgical examination. The EMTEC Corporation will bill the 
manufacturer and send the results of the required inspection to the 
airplane owner/operator. This will further reduce the cost impact upon 
U.S. operators by $8,400 from $56,392 to $47,992.
    In addition, if the required examination reveals a fine equi-axed 
grain structure, replacing the spar cap will be required at a cost of 
approximately $100,000, parts and labor included. If the required 
examination reveals an unusual grain structure that was not a fine 
equi-axed structure, inspecting the spar cap for stress corrosion will 
be required at a cost of approximately $2,750 (50 workhours at $55 per 
hour). An airplane affected by this AD could have a compliance cost as 
low as $1,007 if the spar cap was found acceptable during the 
metallurgical examination, and as high as approximately $100,857 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 a metallurgical examination is necessary: 
$1,007-$150 (cost incurred by manufacturer)=$857 x 0.8145 (capital 
recovery factor at an interest rate of 7 percent)=$70 annualized cost; 
or
     If replacing the spar cap is necessary: approximately 
$100,857 x 0.8145 (capital recovery factor at an interest rate of 7 
percent)=$8,215 annualized cost.
    The required AD's from Dockets No. 92-CE-38-AD (for Model 690B), 
No. 92-CE-43-AD (for Model 500S), and 92-CE-58-AD (for both Models 500S 
and 690B) also affect certain airplanes included in this AD. The 
compliance costs of these other AD's add to the cost discussed above. 
However, replacing the spar cap is only 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.
    Of the 56 U.S.-registered airplanes affected by this AD that have 
not complied with Twin Commander SB No. 215, dated March 3, 1992, no 
owner owns more than one. Of these 56 different owners, 50 are 
businesses, not-for-profit enterprises, or state or local governments; 
and six are individuals.
    The FAA cannot determine the sizes of all the 50 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 
proposal will 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:

94-04-11 Twin Commander Aircraft Corporation: Amendment 39-8831; 
Docket No. 92-CE-26-AD.

    Applicability: The following Model and serial number airplanes, 
certificated in any category: 

------------------------------------------------------------------------
              Model                             Serial Nos.             
------------------------------------------------------------------------
500S.............................  3314 through 3323.                   
690B.............................  11480 through 11566.                 
------------------------------------------------------------------------

    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 stress 
corrosion cracks in the wing front spar lower cap, accomplish the 
following:
    (a) Remove a sample (coupon) of the wing front spar lower cap in 
accordance with the INSTRUCTIONS: PART I section (Model 500S 
airplanes) or the INSTRUCTIONS: PART II section (Models 690B 
airplanes) of Twin Commander Service Bulletin (SB) No. 215, dated 
March 3, 1992, as applicable. Prior to further flight, send this 
coupon for a metallurgical examination to the EMTEC Corporation, 124 
East Sheridan, suite 101, Oklahoma City, Oklahoma 73104, and wait 
for the results of the examination.

    Note 1: The manufacturer will incur the cost of the required 
metallurgical examination. The EMTEC Corporation will bill the 
manufacturer and send the results of the inspection to the airplane 
owner/operator.

    (b) If the results of the metallurgical examination required by 
paragraph (a) of this AD reveal a fine equi-axed grain structure, 
prior to further flight, replace the wing front spar lower cap in 
accordance with the instructions in one of the following, as 
applicable:
    (1) For Model 690B, Twin Commander Custom Kit No. CK-144, 
Revision A, dated November 12, 1992;
    (2) For Model 500S, Twin Commander Custom Kit No. CK-145, dated 
August 21, 1992; or
    (3) For Model 690B, AVIADESIGN, Inc. Supplemental Type 
Certificate SA5740NM.

    Note 2: A fine equi-axed grain structure refers to a grain 
structure that is approximately equal in all three axes and the 
grains are considerably smaller than what is typical of the wing 
spar extrusion. This is in contrast to the elongated, highly 
directional grain structure with relatively large grains typical of 
the wing spar extrusion.

    (c) If the results of the metallurgical examination required by 
paragraph (a) of this AD reveal a grain structure that is smaller 
than the large elongated grains, but not fine equi-axed, prior to 
further flight, inspect the wing front spar lower cap for stress 
corrosion cracking in accordance with an inspection procedure 
approved by the Manager, Seattle Aircraft Certification Office 
(ACO), FAA, Northwest Mountain Region.
    (1) Send the result of this inspection in writing to the FAA at 
the address specified in paragraph (e) of this AD, within 10 days 
after the inspection or 15 days after the effective date of this AD, 
whichever occurs later. State whether any cracks or corrosion was 
found, the location and length of any cracks found, and the location 
and depth of any corrosion found. (Reporting approved by the Office 
of Management and Budget under OMB No. 2120-0056).
    (2) If any cracks are found, 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 Model 690B, Twin Commander Custom Kit No. CK-144, 
Revision A, dated November 12, 1992;
    (ii) For Model 500S, Twin Commander Custom Kit No. CK-145, dated 
August 21, 1992; or
    (iii) For Model 690B, AVIADESIGN, Inc. Supplemental Type 
Certificate SA5740NM.
    (d) 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.
    (e) 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 3: 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.

    (f) The inspections required by this AD shall be done in 
accordance with Twin Commander Service Bulletin, No. 215, dated 
March 3, 1992. 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 
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.
    (g) This amendment (39-8831) becomes effective on April 11, 
1994.

    Issued in Kansas City, Missouri, on February 14, 1994.
Barry D. Clements,
Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. 94-3842 Filed 2-18-94; 8:45 am]
BILLING CODE 4910-13-U