[Federal Register Volume 78, Number 156 (Tuesday, August 13, 2013)]
[Proposed Rules]
[Pages 49207-49213]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2013-19638]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2013-0725; Directorate Identifier 98-CE-01-AD]
RIN 2120-AA64
Airworthiness Directives; Maule Aerospace Technology, Inc.
Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
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SUMMARY: We propose to revise airworthiness directive (AD) 98-15-18
that applies to certain Maule Aerospace Technology, Inc. M-4, M-5, M-6,
M-7, MT-7, MX-7, MXT-7, and M-8 airplanes that are equipped with rear
wing lift struts, part number (P/N) 2079E, and/or front wing lift
struts, P/N 2080E. AD 98-15-18 currently requires repetitively
inspecting certain wing lift struts for internal corrosion and
replacing of any wing lift strut where corrosion is found. Since we
issued AD 98-15-18, we have been informed by the manufacturer that
Model MXT-7-420 airplanes are no longer in existence, are no longer
type certificated, and should be removed from the Applicability
section. We have also been informed that paragraph (b) in AD 98-15-18
is being misinterpreted and is causing confusion. This proposed AD
would remove Model MXT-7-420 airplanes from the Applicability section
and clarify the intent of the language currently in paragraph (b) of AD
98-15-18. This proposed AD would retain all other requirements of the
existing AD. We are proposing this AD to correct the unsafe condition
on these products.
DATES: We must receive comments on this proposed AD by September 27,
2013.
ADDRESSES: You may send comments, using the procedures found in 14 CFR
11.43 and 11.45, by any of the following methods:
Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
Fax: 202-493-2251.
Mail: U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue SE., Washington, DC 20590.
Hand Delivery: Deliver to Mail address above between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
For service information identified in this proposed AD, contact
Maule Air, Inc., 2099 GA Hwy 133 South, Moultrie, Georgia 31768;
telephone: (229) 985-2045; fax: (229) 890-2402; Internet: http://www.mauleairinc.com/pdf/servicebulletins/service_bulletin_11_old.pdf. You may review copies of the referenced service information at
the FAA, Small Airplane Directorate, 901 Locust, Kansas City, Missouri
64106. For information on the availability of this material at the FAA,
call (816) 329-4148.
Examining the AD Docket
You may examine the AD docket on the Internet at http://www.regulations.gov; or in person at the Docket Management Facility
between 9 a.m. and 5 p.m., Monday through Friday, except Federal
holidays. The AD docket contains this proposed AD, the regulatory
evaluation, any comments received, and other information. The street
address for the Docket Office (phone: 800-647-5527) is in the ADDRESSES
section. Comments will be available in the AD docket shortly after
receipt.
[[Page 49208]]
FOR FURTHER INFORMATION CONTACT: Gregory ``Keith'' Noles, Aerospace
Engineer, FAA, Atlanta Aircraft Certification Office, 1701 Columbia
Avenue, College Park, Georgia 30337; phone: (404) 474-5551; fax: (404)
474-5606; email: [email protected].
SUPPLEMENTARY INFORMATION:
Comments Invited
We invite you to send any written relevant data, views, or
arguments about this proposed AD. Send your comments to an address
listed under the ADDRESSES section. Include ``Docket No. FAA-2013-0725;
Directorate Identifier 98-CE-01-AD'' at the beginning of your comments.
We specifically invite comments on the overall regulatory, economic,
environmental, and energy aspects of this proposed AD. We will consider
all comments received by the closing date and may amend this proposed
AD because of those comments.
We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We
will also post a report summarizing each substantive verbal contact we
receive about this proposed AD.
Discussion
On July 14, 1998, we issued AD 98-15-18, Amendment 39-10669 (63 FR
39018, July 21, 1998), and later reissued with a correction on
September 18, 1998 (63 FR 51520, September 28, 1998), (``AD 98-15-
18''), for certain Maule Aerospace Technology Corp. (currently Maule
Aerospace Technology, Inc.) M-4, M-5, M-6, M-7, MX-7, and MXT-7 series
airplanes and Models MT-7-235 and M-8-235 airplanes equipped with
original equipment (OEM) manufacture Maule Aerospace Technology, Inc.
rear wing lift struts, part number (P/N) 2079E, and/or front wing lift
struts, P/N 2080E (or FAA-approved equivalent part numbers). AD 98-15-
18 superseded AD 95-26-18, Amendment 39-9476 (61 FR 623, January 9,
1996), (``AD 95-26-18''), and requires repetitively inspecting the wing
lift struts for corrosion and replacing any wing lift strut where
corrosion is found with either an OEM airworthy part or a new sealed
wing lift strut. Installing a new sealed wing lift strut is a
terminating action for the repetitive inspection and replacement
requirements.
AD 95-26-18 required a one-time inspection of certain wing lift
struts for internal corrosion and replacement of any wing lift strut
where corrosion was found. AD 95-26-18 resulted from reports of an
accident where the wing separated from one of the affected airplanes.
AD 98-15-18 resulted from a need to require the inspections to be
repetitive and to provide the option of using ultrasonic procedures to
accomplish the inspection requirements.
We issued both ADs to detect and correct corrosion on the front and
rear wing lift struts, which could cause the wing lift strut to fail.
This failure could result in the wing separating from the airplane.
Actions Since AD 98-15-18 Was Issued
Since we issued AD 98-15-18, we have been informed by the
manufacturer that only one Model MXT-7-420 airplane was built and was
later dismantled and removed from the type certificate data sheet
(TCDS).
We have also been informed that the language in paragraph (b) of AD
98-15-18 has been misinterpreted and has caused confusion. Paragraph
(b) of AD 98-15-18 currently states, ``If holes are drilled into the
sealed wing lift strut assemblies installed as specified in paragraph
(a)(4) of this AD in order to attach cuffs, door clips, or other
hardware, inspect the wing lift struts at intervals not to exceed 24
calendar months using the procedures specified in either paragraph
(a)(1) or (a)(2), including all subparagraphs, of this AD.''
Our intention was to specify that if a sealed wing lift strut
assembly is installed as a replacement part, the repetitive inspection
requirement is terminated only if the seal is never improperly broken.
We also intended to specify that if the seal is improperly broken, then
that wing lift strut becomes subject to continued repetitive
inspections.
We did not intend to promote drilling holes into or otherwise
unsealing a sealed strut. Properly unsealing and resealing a sealed
wing lift strut is still considered a terminating action for the
repetitive inspection requirements of this proposed AD as long as all
appropriate regulations and issues are considered, such as static
strength, fatigue, material effects, immediate and long-term (internal
and external) corrosion protection, resealing methods, etc. Current FAA
regulations in 14 CFR 43.13(b) specify that maintenance performed will
result in the part's condition to be at least equal to its original or
properly altered condition. There are provisions in this proposed AD
for approving such actions as an alternative method of compliance
(AMOC).
FAA's Determination
We are proposing this AD because we evaluated all the relevant
information and determined the unsafe condition described previously is
likely to exist or develop in other products of the same type design.
Proposed AD Requirements
This proposed AD would retain all requirements of AD 98-15-18 and
would remove Model MXT-7-420 airplanes from the Applicability section.
This proposed AD would also clarify our intent of required actions if
the seal on a sealed wing lift strut is ever improperly broken.
Paragraph Designation Changes to AD 98-15-18
Since AD 98-15-18 was issued, the AD format has been revised, and
certain paragraphs have been rearranged. As a result, the corresponding
paragraph identifiers have changed in this proposed AD, as listed in
the following table:
Table 1--Revised Paragraph Identifiers
------------------------------------------------------------------------
Corresponding requirement in this
Requirement in AD 99-01-05 proposed AD
------------------------------------------------------------------------
paragraph (a) paragraph (h)
paragraph (a)(1) paragraph (i)(1)
paragraph (a)(1)(i) paragraph (i)(1)(i)
paragraph (a)(1)(ii) paragraph (i)(1)(ii)
paragraph (a)(2) paragraph (i)(2)
paragraph (a)(2)(i) paragraph (i)(2)(i)
paragraph (a)(2)(ii) paragraph (i)(2)(ii)
paragraph (a)(3) paragraph (j)(1)
paragraph (a)(4) and (c) paragraph (j)(2)
paragraph (b) removed
------------------------------------------------------------------------
Costs of Compliance
We estimate that this proposed AD affects 1,196 airplanes of U.S.
registry.
We estimate the following costs to comply with this proposed AD.
However, the only difference in the costs presented below and the costs
associated with AD 98-15-18 is the change in the labor rate from $65
per hour to $85 per hour.
[[Page 49209]]
Estimated Costs
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Cost on U.S.
Action Labor cost Parts cost Cost per product operators
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Inspection of the wing lift 11 x $85 per hour = $40 $975 per inspection $1,166,100 per
struts. $935 per cycle. inspection cycle.
inspection cycle.
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We estimate the following costs to do any necessary replacements
that would be required based on the results of the proposed inspection.
We have no way of determining the number of airplanes that might need
these replacements:
On-Condition Costs
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Cost per
Action Labor cost per wing lift strut Parts cost per product per
wing lift strut wing lift strut
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Replacement of the wing lift strut........... 5 work-hours x $85 per hour = $500 $925
$425.
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Authority for This Rulemaking
Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, section 106, describes the
authority of the FAA Administrator. Subtitle VII, Aviation Programs,
describes in more detail the scope of the Agency's authority.
We are issuing this rulemaking under the authority described in
Subtitle VII, Part A, Subpart III, section 44701, ``General
requirements.'' Under that section, Congress charges the FAA with
promoting safe flight of civil aircraft in air commerce by prescribing
regulations for practices, methods, and procedures the Administrator
finds necessary for safety in air commerce. This regulation is within
the scope of that authority because it addresses an unsafe condition
that is likely to exist or develop on products identified in this
rulemaking action.
Regulatory Findings
We have determined that this proposed AD would not have federalism
implications under Executive Order 13132. This proposed AD would not
have a substantial direct effect 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.
For the reasons discussed above, I certify that the proposed
regulation:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Is not a ``significant rule'' under the DOT Regulatory Policies
and Procedures (44 FR 11034, February 26, 1979),
(3) Will not affect intrastate aviation in Alaska, and
(4) Will not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.
The Proposed Amendment
Accordingly, under the authority delegated to me by the
Administrator, the FAA proposes to amend 14 CFR part 39 as follows:
PART 39--AIRWORTHINESS DIRECTIVES
0
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
0
2. The FAA amends Sec. 39.13 by removing airworthiness directive (AD)
98-15-18, Amendment 39-10669 (63 FR 39018, July 21, 1998), and adding
the following new AD:
Maule Aerospace Technology, Inc.: Docket No. FAA-2013-0725;
Directorate Identifier 98-CE-01-AD.
(a) Comments Due Date
The FAA must receive comments on this AD action by September 27,
2013.
(b) Affected ADs
This AD revises AD 98-15-18, Amendment 39-10669 (63 FR 39018,
July 21, 1998), which superseded AD 95-26-18, Amendment 39-9476 (61
FR 623, January 9, 1996.)
(c) Applicability
This AD applies to the following Maule Aerospace Technology,
Inc. airplanes, all serial numbers, identified in table 1 of
paragraph (c) of this AD, that are:
(1) Equipped with original equipment manufacturer (OEM) Maule
Aerospace Technology, Inc. rear wing lift struts, part number (P/N)
2079E (or FAA-approved equivalent part numbers), and/or front wing
lift struts, P/N 2080E (or FAA-approved equivalent part numbers);
and
(2) certificated in any category.
Table 1 to Paragraph (c) of This AD--Applicability
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Models
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Bee Dee M-4..................... M-4............... M-4C.............. M-4S.............. M-4T
M-4-180C........................ M-4-180S.......... M-4-180T.......... M-4-210........... M-4-210C
M-4-210S........................ M-4-210T.......... M-4-220........... M-4-220C.......... M-4-220S
M-4-220T........................ M-5-180C.......... M-5-200........... M-5-210C.......... M-5-210TC
M-5-220C........................ M-5-235C.......... M-6-180........... M-6-235........... M-7-235
M-7-235A........................ M-7-235B.......... M-7-235C.......... MT-7-235.......... MX-7-160
MX-7-180........................ MX-7-180A......... MX-7-180B......... MX-7-235.......... MX-7-420
MXT-7-160....................... MXT-7-180......... MXT-7-180A........ M-8-235 ..................
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[[Page 49210]]
Note 1 to paragraph (c) of this AD: This AD does not apply to
airplanes equipped with four Maule sealed lift struts, P/N 2200E and
P/N 2201E. These sealed lift struts are identified by two raised
weld spots on the upper end of the strut just below the serial
number plate. Removal of the upper cuff is needed to locate the weld
spots.
(d) Subject
Joint Aircraft System Component (JASC)/Air Transport Association
(ATA) of America Code 57, Wings.
(e) Unsafe Condition
The subject of this AD was originally prompted by reports of
corrosion damage found on the wing lift struts. We are revising AD
98-15-18, Amendment 39-10669 (63 FR 39018, July 21, 1998), because
of reports that the language currently in paragraph (b) is being
misinterpreted and is causing confusion. Since we issued AD 98-15-
18, we have been informed by the manufacturer that Model MXT-7-420
airplanes are no longer in existence, are no longer type
certificated, and should be removed from the Applicability section.
This AD removes Model MXT-7-420 airplanes from the Applicability
section and clarifies the intent of the language currently in
paragraph (b) of AD 98-15-18, which is being removed by this AD. Our
intention was to specify that if a sealed wing lift strut assembly
is installed as a replacement part, the repetitive inspection
requirement is terminated only if the seal is never improperly
broken. This AD also retains all the actions currently required in
AD 98-15-18. There are no new requirements in this AD and it does
not add any additional burden to the owners/operators of the
affected airplanes. We are issuing this AD to detect and correct
corrosion on the front and rear wing lift struts, which could cause
the wing lift strut to fail. This failure could result in the wing
separating from the airplane.
(f) Paragraph Designation Changes to AD 98-15-18
Since AD 98-15-18, Amendment 39-10669 (63 FR 39018, July 21,
1998), was issued, the AD format has been revised, and certain
paragraphs have been rearranged. As a result, the corresponding
paragraph identifiers have changed in this AD, as listed in the
following table:
Table 2 to Paragraph (f) of This AD--Revised Paragraph Identifiers
------------------------------------------------------------------------
Corresponding requirement in this
Requirement in AD 98-15-18 AD
------------------------------------------------------------------------
paragraph (a) paragraph (h)
paragraph (a)(1) paragraph (i)(1)
paragraph (a)(1)(i) paragraph (i)(1)(i)
paragraph (a)(1)(ii) paragraph (i)(1)(ii)
paragraph (a)(2) paragraph (i)(2)
paragraph (a)(2)(i) paragraph (i)(2)(i)
paragraph (a)(2)(ii) paragraph (i)(2)(ii)
paragraph (a)(3) paragraph (j)(1)
paragraph (a)(4) and (c) paragraph (j)(2)
paragraph (b) Removed
------------------------------------------------------------------------
(g) Compliance
Unless already done (compliance with AD 98-15-18, Amendment 39-
10669 (63 FR 39018, July 21, 1998)), do the following actions within
the compliance times specified in paragraphs (h) through (j) of this
AD, including all subparagraphs.
Note 2 to paragraph (g) of this AD: This AD does not require any
actions over that already required by AD 98-15-18, Amendment 39-
10669 (63 FR 39018, July 21, 1998). This AD clarifies the FAA's
intention that if a sealed wing lift strut assembly is installed as
a replacement part, the repetitive inspection requirement is
terminated only if the seal is never improperly broken. If the seal
is improperly broken, then that wing lift strut becomes subject to
continued repetitive inspections. We did not intend to promote
drilling holes into or otherwise unsealing a sealed strut. Properly
unsealing and resealing a sealed wing lift strut is still considered
a terminating action for the repetitive inspection requirements of
this AD as long as all appropriate regulations and issues are
considered, such as static strength, fatigue, material effects,
immediate and long-term (internal and external) corrosion
protection, resealing methods, etc.
(h) Remove Wing Lift Struts
At whichever of paragraphs (h)(1), (h)(2), or (h)(3) of this AD
that occurs later, remove the wing lift struts following the
INSTRUCTIONS section in PART I of Maule Air, Inc. Service Bulletin
(Maule SB) No. 11, dated October 30, 1995. Before further flight
after the removal, do one of the actions in either paragraph (i)(1),
(i)(2), (j)(1), or (j)(2) of this AD, including all subparagraphs.
(1) Upon accumulating 2 years time-in-service on an OEM Maule
wing lift strut, P/N 2079E and/or P/N 2080E;
(2) Within 3 calendar months after September 9, 1998 (the
effective date retained from AD 98-15-18, Amendment 39-10669 (63 FR
39018, July 21, 1998)); or
(3) Within 2 years after the last inspection done in accordance
with AD 95-26-18, Amendment 39-9476 (61 FR 623, January 9, 1996)
(which was superseded by AD 98-15-18).
(i) Inspect Wing Lift Struts
(1) Before further flight after the removal required in
paragraph (h) of this AD, inspect each wing lift strut for corrosion
and perceptible dents following the INSTRUCTIONS section in PART I
of Maule SB No. 11, dated October 30, 1995.
(i) If no corrosion is visible and no perceptible dents are
found on any wing lift strut during the inspection required in
paragraph (i)(1) of this AD, before further flight, apply corrosion
inhibitor to each wing lift strut. Apply the corrosion inhibitor
following the INSTRUCTIONS section in PART I of Maule SB No. 11,
dated October 30, 1995. Repetitively thereafter inspect each wing
lift strut at intervals not to exceed 24 calendar months following
the procedures in paragraph (i)(1) or (i)(2) of this AD, including
all subparagraphs.
(ii) If corrosion or perceptible dents are found on any wing
lift strut during the inspection required in paragraph (i)(1) of
this AD or during any repetitive inspection required in paragraph
(i)(1)(i) of this AD, before further flight, replace the affected
wing lift strut with one of the replacement options specified in
paragraph (j)(1) or (j)(2) of this AD. Do the replacement following
the procedures specified in those paragraphs, as applicable.
(2) Before further flight after the removal required in
paragraph (h) of this AD, inspect each wing lift strut for corrosion
following the procedures in the Appendix to this AD. This inspection
must be done by a Level 2 or Level 3 inspector certified using the
guidelines established by the American Society for Non-destructive
Testing or the ``Military Standard for Nondestructive Testing
Personnel Qualification and Certification'' (MIL-STD-410E).
(i) If no corrosion is found on any wing lift strut during the
inspection specified in paragraph (i)(2) of this AD and all
requirements in the Appendix to this AD are met, before further
flight apply corrosion inhibitor to each wing lift strut following
INSTRUCTIONS section in PART I of Maule SB No. 11, dated October 30,
1995. Repetitively thereafter inspect each wing lift strut every 24
calendar months provided no corrosion is found and all of the
requirements in the Appendix of this AD are met.
(ii) If corrosion is found on any wing lift strut during the
inspection required paragraph (i)(2) of this AD or during any
repetitive inspection required in paragraph (i)(2)(i) of this AD, or
if any requirement in the Appendix of this AD is not met, before
further flight after any inspection in which corrosion is found or
the Appendix requirements are not met, replace the affected wing
lift strut with one of the replacement options specified in
paragraph (j)(1) or (j)(2) of this AD. Do the replacement following
the procedures specified in those paragraphs, as applicable.
(j) Wing Lift Strut Replacement Options
(1) Install OEM Maule P/N wing lift struts (or FAA-approved
equivalent part numbers) that have been inspected following the
procedures in either paragraph (i)(1) or (i)(2) of this AD,
including all subparagraphs, and are found to be airworthy. Do the
installations following the INSTRUCTIONS section in PART II of Maule
SB No. 11, dated October 30, 1995. Repetitively thereafter inspect
the newly installed wing lift struts at intervals not to exceed 24
calendar months following the procedures in either paragraph (i)(1)
or (i)(2) of this AD, including all subparagraphs.
(2) Install new Maule sealed wing lift struts, P/N 2200E or P/N
2201E, as applicable (or FAA-approved equivalent part numbers)
following the INSTRUCTIONS section in PART II of Maule SB No. 11,
dated October 30, 1995. Installing one of these new sealed wing lift
strut assemblies terminates the repetitive inspection requirements
in paragraphs (i)(1) or (i)(2) of this AD, including all
subparagraphs, for that wing lift strut assembly.
[[Page 49211]]
(k) Alternative Methods of Compliance (AMOCs)
(1) The Manager, Atlanta Aircraft Certification Office, (ACO),
FAA, has the authority to approve AMOCs for this AD, if requested
using the procedures found in 14 CFR 39.19. In accordance with 14
CFR 39.19, send your request to your principal inspector or local
Flight Standards District Office, as appropriate. If sending
information directly to the manager of the ACO, send it to the
attention of the person identified in the Related Information
section of this AD.
(2) Before using any approved AMOC, notify your appropriate
principal inspector, or lacking a principal inspector, the manager
of the local flight standards district office/certificate holding
district office.
(3) AMOCs approved for AD 98-15-18, Amendment 39-10669 (63 FR
39018, July 21, 1998) and AD 95-26-18, Amendment 39-9476 (61 FR 623,
January 9, 1996) are approved as AMOCs for this AD.
(l) Related Information
(1) For more information about this AD, contact Gregory K.
Noles, Aerospace Engineer, FAA, Atlanta ACO, 1701 Columbia Avenue,
College Park, Georgia 30337; phone: (404) 474-5551; fax: (404) 474-
5606; email: [email protected].
(2) For service information identified in this AD, contact Maule
Air, Inc., 2099 GA Hwy 133 South, Moultrie, Georgia 31768;
telephone: (229) 985-2045; fax: (229) 890-2402; Internet: http://www.mauleairinc.com/pdf/servicebulletins/service_bulletin_11_old.pdf. You may review copies of the referenced service information
at the FAA, Small Airplane Directorate, 901 Locust, Kansas City,
Missouri 64106. For information on the availability of this material
at the FAA, call (816) 329-4148.
Appendix To Docket No. FAA-2013-0725
Procedures and Requirements for Ultrasonic Inspection of Maule Wing
Lift Struts
Equipment Requirements
1. A portable ultrasonic thickness gauge or flaw detector with
echo-to-echo digital thickness readout capable of reading to 0.001-
inch and an A-trace waveform display will be needed to do this
inspection.
2. An ultrasonic probe with the following specifications will be
needed to do this inspection: 10 MHz (or higher), 0.283-inch (or
smaller) diameter dual element or delay line transducer designed for
thickness gauging. The transducer and ultrasonic system shall be
capable of accurately measuring the thickness of AISI 4340 steel
down to 0.020-inch. An accuracy of +/- 0.002-inch throughout a
0.020-inch to 0.050-inch thickness range while calibrating shall be
the criteria for acceptance.
3. Either a precision machined step wedge made of 4340 steel (or
similar steel with equivalent sound velocity) or at least three shim
samples of same material will be needed to do this inspection. One
thickness of the step wedge or shim shall be less than or equal to
0.020-inch, one shall be greater than or equal to 0.050-inch and at
least one other step or shim shall be between these two values.
4. Glycerin, light oil, or similar non-water based ultrasonic
couplants are recommended in the setup and inspection procedures.
Water-based couplants, containing appropriate corrosion inhibitors,
may be utilized, provided they are removed from both the reference
standards and the test item after the inspection procedure is
completed and adequate corrosion prevention steps are then taken to
protect these items.
Note: Couplant is defined as ``a substance used between
the face of the transducer and test surface to improve transmission
of ultrasonic energy across the transducer/strut interface.''
Note: If surface roughness due to paint loss or
corrosion is present, the surface should be sanded or polished
smooth before testing to assure a consistent and smooth surface for
making contact with the transducer. Care shall be taken to remove a
minimal amount of structural material. Paint repairs may be
necessary after the inspection to prevent further corrosion damage
from occurring. Removal of surface irregularities will enhance the
accuracy of the inspection technique.
Instrument Setup
1. Set up the ultrasonic equipment for thickness measurements as
specified in the instrument's user's manual. Because of the variety
of equipment available to perform ultrasonic thickness measurements,
some modification to this general setup procedure may be necessary.
However, the tolerance requirement of step 13 and the record keeping
requirement of step 14, must be satisfied.
2. If battery power will be employed, check to see that the
battery has been properly charged. The testing will take
approximately two hours. Screen brightness and contrast should be
set to match environmental conditions.
3. Verify that the instrument is set for the type of transducer
being used, i.e. single or dual element, and that the frequency
setting is compatible with the transducer.
4. If a removable delay line is used, remove it and place a drop
of couplant between the transducer face and the delay line to assure
good transmission of ultrasonic energy. Reassemble the delay line
transducer and continue.
5. Program a velocity of 0.231-inch/microsecond into the
ultrasonic unit unless an alternative instrument calibration
procedure is used to set the sound velocity.
6. Obtain a step wedge or steel shims per item 3 of the
Equipment Requirements. Place the probe on the thickest sample using
couplant. Rotate the transducer slightly back and forth to ``ring''
the transducer to the sample. Adjust the delay and range settings to
arrive at an A-trace signal display with the first backwall echo
from the steel near the left side of the screen and the second
backwall echo near the right of the screen. Note that when a single
element transducer is used, the initial pulse and the delay line/
steel interface will be off of the screen to the left. Adjust the
gain to place the amplitude of the first backwall signal at
approximately 80% screen height on the A-trace.
7. ``Ring'' the transducer on the thinnest step or shim using
couplant. Select positive half-wave rectified, negative half-wave
rectified, or filtered signal display to obtain the cleanest signal.
Adjust the pulse voltage, pulse width, and damping to obtain the
best signal resolution. These settings can vary from one transducer
to another and are also user dependent.
8. Enable the thickness gate, and adjust the gate so that it
starts at the first backwall echo and ends at the second backwall
echo. (Measuring between the first and second backwall echoes will
produce a measurement of the steel thickness that is not affected by
the paint layer on the strut). If instability of the gate trigger
occurs, adjust the gain, gate level, and/or damping to stabilize the
thickness reading.
9. Check the digital display reading and if it does not agree
with the known thickness of the thinnest thickness, follow your
instrument's calibration recommendations to produce the correct
thickness reading. When a single element transducer is used this
will usually involve adjusting the fine delay setting.
10. Place the transducer on the thickest step of shim using
couplant. Adjust the thickness gate width so that the gate is
triggered by the second backwall reflection of the thick section. If
the digital display does not agree with the thickest thickness,
follow your instruments calibration recommendations to produce the
correct thickness reading. A slight adjustment in the velocity may
be necessary to get both the thinnest and the thickest reading
correct. Document the changed velocity value.
11. Place couplant on an area of the lift strut which is thought
to be free of corrosion and ``ring'' the transducer to surface.
Minor adjustments to the signal and gate settings may be required to
account for coupling improvements resulting from the paint layer.
The thickness gate level should be set just high enough so as not to
be triggered by irrelevant signal noise. An area on the upper
surface of the lift strut above the inspection area would be a good
location to complete this step and should produce a thickness
reading between 0.034-inch and 0.041-inch.
12. Repeat steps 8, 9, 10, and 11 until both thick and thin shim
measurements are within tolerance and the lift strut measurement is
reasonable and steady.
13. Verify that the thickness value shown in the digital display
is within +/- 0.002-inch of the correct value for each of the three
or more steps of the setup wedge or shims. Make no further
adjustments to the instrument settings.
14. Record the ultrasonic versus actual thickness of all wedge
steps or steel shims available as a record of setup.
Inspection Procedure
1. Clean the lower 18 inches of the wing lift struts using a
cleaner that will remove all dirt and grease. Dirt and grease will
adversely affect the accuracy of the inspection technique. Light
sanding or polishing may also be required to reduce surface
roughness as noted in the Equipment Requirements section.
2. Using a flexible ruler, draw a \1/4\-inch grid on the surface
of the first 11 inches from
[[Page 49212]]
the lower end of the strut as shown in Maule Air, Inc. Service
Bulletin No. 11, dated October 30, 1995, as applicable. This can be
done using a soft (2) pencil and should be done on both
faces of the strut. As an alternative to drawing a complete grid,
make two rows of marks spaced every \1/4\-inch across the width of
the strut. One row of marks should be about 11 inches from the lower
end of the strut, and the second row should be several inches away
where the strut starts to narrow. Lay the flexible ruler between
respective tick marks of the two rows and use tape or a rubber band
to keep the ruler in place. See Figure 1.
3. Apply a generous amount of couplant inside each of the square
areas or along the edge of the ruler. Re-application of couplant may
be necessary.
4. Place the transducer inside the first square area of the
drawn grid or at the first \1/4\-inch mark on the ruler and ``ring''
the transducer to the strut. When using a dual element transducer,
be very careful to record the thickness value with the axis of the
transducer elements perpendicular to any curvature in the strut. If
this is not done, loss of signal or inaccurate readings can result.
5. Take readings inside each square on the grid or at \1/4\-inch
increments along the ruler and record the results. When taking a
thickness reading, rotate the transducer slightly back and forth and
experiment with the angle of contact to produce the lowest thickness
reading possible. Pay close attention to the A-scan display to
assure that the thickness gate is triggering off of maximized
backwall echoes.
Note: A reading shall not exceed .041 inch. If a
reading exceeds .041 inch, repeat steps 13 and 14 of the Instrument
Setup section before proceeding further.
6. If the A-trace is unsteady or the thickness reading is
clearly wrong, adjust the signal gain and/or gate setting to obtain
reasonable and steady readings. If any instrument setting is
adjusted, repeat steps 13 and 14 of the Instrument Setup section
before proceeding further.
7. In areas where obstructions are present, take a data point as
close to the correct area as possible.
Note: The strut wall contains a fabrication bead at
approximately 40% of the strut chord. The bead may interfere with
accurate measurements in that specific location.
8. A measurement of 0.024-inch or less shall require replacement
of the strut prior to further flight
9. If at any time during testing an area is encountered where a
valid thickness measurement cannot be obtained due to a loss of
signal strength or quality, the area shall be considered suspect.
These areas may have a remaining wall thickness of less than 0.020-
inch, which is below the range of this setup, or they may have small
areas of localized corrosion or pitting present. The latter case
will result in a reduction in signal strength due to the sound being
scattered from the rough surface and may result in a signal that
includes echoes from the pits as well as the backwall. The suspect
area(s) shall be tested with a Maule ``Fabric Tester'' as specified
in Maule Air, Inc. Service Bulletin No. 11, dated October 30, 1995.
10. Record the lift strut inspection in the aircraft log book.
[GRAPHIC] [TIFF OMITTED] TP13AU13.009
[[Page 49213]]
Issued in Kansas City, Missouri, on August 6, 2013.
Earl Lawrence,
Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. 2013-19638 Filed 8-12-13; 8:45 am]
BILLING CODE 4910-13-P