[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
