[Federal Register Volume 63, Number 56 (Tuesday, March 24, 1998)]
[Proposed Rules]
[Pages 14051-14055]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-7522]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 98-CE-01-AD]
RIN 2120-AA64
Airworthiness Directives; Maule Aerospace Technology Corp. 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
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed rulemaking (NPRM).
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SUMMARY: This document proposes to supersede Airworthiness Directive
(AD) 95-26-18, which currently requires inspecting (one-time) certain
wing lift struts for internal corrosion on Maule Aerospace Technology
Corp. (Maule) 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, and replacing any wing lift
strut where corrosion is found. That AD was the result of a report of
an accident where the wing separated from one of the affected
airplanes. The proposed AD would retain the initial inspection and
possible replacement requirements of AD 95-26-18, would require the
inspections to be repetitive, and would provide the option of using
ultrasonic procedures to accomplish the inspection requirements. The
actions specified by the proposed AD are intended to prevent failure of
the wing lift struts caused by corrosion damage, which could eventually
result in the wing separating from the airplane.
DATES: Comments must be received on or before May 22, 1998.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Central Region, Office of the Regional Counsel,
Attention: Rules Docket No. 98-CE-01-AD, Room 1558, 601 E. 12th Street,
Kansas City, Missouri 64106. Comments may be inspected at this location
between 8 a.m. and 4 p.m., Monday through Friday, holidays excepted.
Service information that applies to the proposed AD may be obtained
from Maule Aerospace Technology Inc., 2099 GA. Highway, 133 South,
Moultrie, Georgia 31768; telephone: (912) 985-2045; facsimile: (912)
890-2402. This information also may be examined at the Rules Docket at
the address above.
FOR FURTHER INFORMATION CONTACT: Cindy Lorenzen, Aerospace Engineer,
FAA, Atlanta Aircraft Certification Office, One Crown Center, 1895
Phoenix Boulevard, suite 450, Atlanta, Georgia 30349; telephone: (770)
703-6078; facsimile: (770) 703-6097.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested persons are invited to participate in the making of the
proposed rule by submitting such written data, views, or arguments as
they may desire. Communications should identify the Rules Docket number
and be submittee in triplicate to the address specified above. All
communications received on or before the closing date for comments,
specified above, will be considered before taking action on the
proposed rule. The proposals contained in this notice may be changed in
light of the comments received.
Comments are specifically invited on the overall regulatory,
economic, environmental, and energy aspects of the proposed rule. All
comments submitted will be available, both before and after the closing
date for comments, in the Rules Docket for examination by interested
persons. A report that summarizes each FAA-public contact concerned
with the substance of this proposal will be filed in the Rules Docket.
Commenters wishing the FAA to acknowledge receipt of their comments
submitted in response to this notice must submit a self-addressed,
stamped postcard on which the following statement is made: ``Comments
to Docket No. 98-CE-01-AD.'' The postcard will be date stamped and
returned to the commenter.
Availability of NPRMs
Any person may obtain a copy of this NPRM by submitting a request
to the FAA, Central Region, Office of the Regional Counsel, Attention:
Rules Docket No. 98-CE-01-AD, Room 1558, 601 E. 12th Street, Kansas
City, Missouri 64106.
Discussion
AD 95-26-18, Amendment 39-9476 (61 FR 623, January 9, 1996),
currently requires the following on Maule Aerospace Technology Corp.
(Maule) 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 that are equipped with part number (P/N)
2079E rear wing lift struts and P/N 2080E front wing lift struts:
inspecting (one-time) the wing lift struts for internal corrosion, and
replacing any wing lift strut where corrosion is found. Accomplishment
of the actions required by AD 95-26-18 is in accordance with
[[Page 14052]]
Maule Service Bulletin (SB) No. 11, Issued: October 30, 1995.
That AD was the result of a report of an accident where the wing
separated from one of the affected airplanes.
The reason the FAA only included a one-time inspection requirement
in AD 95-26-18 rather than a repetitive inspection requirement is that
the nature of the unsafe condition did not allow the FAA to solicit
public comment prior to the issuance of the rule. The Administrative
Procedure Act (APA) requires that each requirement of an AD action be
analyzed separately to determine whether prior public notice is
necessary. Since the repetitive inspections would have been at 2 year
intervals, the FAA could not make an independent finding of
``impractability'' for bypassing prior public comment on the repetitive
inspections; only for the initial inspection and possible replacement
required by AD 95-26-18.
The FAA has approved alternative methods of compliance (AMOC) to
the inspection requirement of AD 95-26-18. The approved AMOC's allow
the inspection to be accomplished using ultrasonic, X-ray, and
borescope procedures.
The FAA's Determination
After examining the circumstances and reviewing all available
information related to the incidents described above, the FAA has
determined the following:
That the wing lift strut inspection required by AD 95-26-
18 should be repetitive;
That the option of using ultrasonic procedures to
accomplish the inspection requirements should be provided; and
That AD action should be taken to prevent failure of the
wing lift struts caused by corrosion damage, which could eventually
result in the wing separating from the airplane.
Explanation of the Provisions of the Proposed AD
Since an unsafe condition has been identified that is likely to
exist or develop in other Maule M-4, M-5, M-6, M-7, MX-7, and MXT-7
series and Models MT-7-235 and M-8-235 airplanes of the same type
design that are equipped with P/N 2079E (or FAA-approved equivalent
part number) rear wing lift struts or P/N 2080E front wing lift struts
(or FAA-approved equivalent part number), the FAA is proposing an AD to
supersede AD 95-26-18. The proposed AD:
Would retain the initial inspection and possible
replacement requirements of AD 95-26-18;
Would require the inspections to be repetitive; and
Would provide the option of using ultrasonic procedures to
accomplish the inspection requirements.
The airplanes affected by the proposed AD could have wing lift
struts installed that have Parts Manufacture Approval (PMA). For those
airplanes having PMA parts that are equivalent (PMA by equivalency) to
those referenced in the proposed AD, the phrase ``or FAA-approved
equivalent part number'' means that the proposed AD applies to
airplanes with PMA by equivalency wing lift struts installed.
Compliance Time of the Proposed AD
The compliance time of the proposed AD is presented in calendar
time instead of hours time-in-service. The FAA has determined that a
calendar time for compliance is the most desirable method because the
unsafe condition described in the proposed AD is caused by corrosion.
Corrosion can occur on airplanes regardless of whether the airplane is
in service.
Cost Impact
The FAA estimates that 1,196 airplanes in the U.S. registry would
be affected by the proposed AD, that it would take 11 workhours per
airplane to accomplish the proposed initial inspection, and that the
average labor rate is approximately $60 an hour. Parts to accomplish
the proposed initial inspection cost approximately $40 per airplane.
Based on these figures, the total cost impact of the proposed AD on
U.S. operators is estimated to be $837,200. This figure only takes into
account the cost of the proposed initial inspection and does not take
into account the cost of the proposed repetitive inspections. The FAA
has no way of determining how many repetitive inspections each owner/
operator of the affected airplanes would incur.
In addition, these figures are based upon the presumption that no
affected airplane operator has accomplished the proposed inspection,
and does not take into account the cost for replacement if corrosion is
found on a wing lift strut. The FAA has no way of determining the
number of wing lift struts that may need to be replaced based upon the
results of the proposed inspections.
Regulatory Impact
The regulations proposed herein would 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 would 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 not a ``significant rule'' under DOT Regulatory Policies and
Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated,
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. A copy of the draft regulatory evaluation
prepared for this action has been placed in the Rules Docket. A copy of
it may be obtained by contacting the Rules Docket at the location
provided under the caption ADDRESSES.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Safety.
The Proposed Amendment
Accordingly, pursuant to the authority delegated to me by the
Administrator, the Federal Aviation Administration proposes to amend 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. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by removing Airworthiness Directive
(AD) 95-26-18, Amendment 39-9476, and by adding a new AD to read as
follows:
Maule Aerospace Technology Corp.: Docket No. 98-CE-01-AD; Supersedes
AD 95-26-18, Amendment 39-9476.
Applicability: The following airplane models, all serial
numbers, certificated in any category; that are equipped with part
number (P/N) 2079E (or FAA-approved equivalent part number) rear
wing lift struts or P/N 2080E (or FAA-approved equivalent part
number) front wing lift struts:
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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
[[Page 14053]]
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............................. MX-7-235............... MX-7-180.............. MX-7-420
MXT-7-180........................... MT-7-235............... M-8-235............... MX-7-160
MXT-7-160........................... MX-7-180A.............. MXT-7-180A............ MX-7-180B
MXT-7-420........................... M-7-235B............... M-7-235A.............. M-7-235C
----------------------------------------------------------------------------------------------------------------
Note 1: The airplanes affected by this AD could have wing lift
struts installed that have Parts Manufacture Approval (PMA). For
those airplanes having PMA parts that are equivalent (PMA by
equivalency) to those referenced in this AD, the phrase ``or FAA-
approved equivalent part number'' means that this AD applies to
airplanes with PMA by equivalency wing lift struts installed.
Note 2: 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.
Note 3: This AD applies to each airplane identified in the
preceding applicability provision, regardless of whether it has been
modified, altered, or repaired in the area subject to the
requirements of this AD. For airplanes that have been modified,
altered, or repaired so that the performance of the requirements of
this AD is affected, the owner/operator must request approval for an
alternative method of compliance in accordance with paragraph (e) of
this AD. The request should include an assessment of the effect of
the modification, alteration, or repair on the unsafe condition
addressed by this AD; and, if the unsafe condition has not been
eliminated, the request should include specific proposed actions to
address it.
Compliance: Required as indicated in the body of this AD, unless
already accomplished.
To prevent failure of the wing lift struts caused by corrosion
damage, which could eventually result in the wing separating from
the airplane, accomplish the following:
Note 4: The paragraph structure of this AD is as follows:
Level 1: (a), (b), (c), etc.
Level 2: (1), (2), (3), etc.
Level 3: (i), (ii), (iii), etc.
Level 2 and Level 3 structures are designations of the Level 1
paragraph they immediately follow.
(a) Upon accumulating 2 years on a lift strut affected by this
AD; within 3 calendar months after the effective date of this AD; or
within 2 years after the last inspection accomplished in accordance
with AD 95-26-18 (superseded by this action), whichever occurs
later, remove the wing lift struts in accordance with the
INSTRUCTIONS section of Maule Service Bulletin (SB) No. 11, Issued:
October 30, 1995, and accomplish one of the following (the actions
in either paragraph (a)(1), (a)(2), (a)(3), or (a)(4), including all
subparagraphs; of this AD):
(1) Inspect the wing lift struts for corrosion in accordance
with the INSPECTION PROCEDURE section of Maule SB No. 11, Issued:
October 30, 1995.
(i) If no perceptible dents (as defined in the above SB) are
found in the wing lift strut and no corrosion is externally visible,
apply corrosion inhibitor to each strut in accordance with Maule SB
No. 11, Issued: October 30, 1995. Reinspect the wing lift struts at
intervals not to exceed 24 calendar months provided no perceptible
dents or external corrosion is found.
(ii) If a perceptible dent (as defined in the above SB) is found
in the wing lift strut or external corrosion is found, prior to
further flight, accomplish one of the installations (and subsequent
actions presented in each paragraph) specified in paragraphs (a)(3)
and (a)(4) of this AD.
(2) Inspect the wing lift struts for corrosion in accordance
with the Appendix to this AD. The inspection procedures in this
Appendix must be accomplished by a Level 2 or Level 3 inspector
certified using the guidelines established by the American Society
for Non-destructive Testing, or MIL-STD-410.
(i) If no external corrosion is found and all requirements in
the Appendix to this AD are met, prior to further flight, apply
corrosion inhibitor to each strut in accordance with Maule SB No.
11, Issued: October 30, 1995. Reinspect the lift struts at intervals
not to exceed 24 calendar months provided no external corrosion is
found and all of the requirements included in the Appendix of this
AD are met.
(ii) If external corrosion is found or if any of the
requirements in the Appendix of this AD are not met, prior to
further flight, accomplish one of the installations (and subsequent
actions presented in each paragraph) specified in paragraphs (a)(3)
and (a)(4) of this AD.
(3) Install original equipment manufacturer (OEM) part number
wing lift struts (or FAA-approved equivalent part numbers) that have
been inspected in accordance with the specifications presented in
either paragraph (a)(1) or (a)(2) of this AD, and are found to be
airworthy according to the inspection requirements included in these
paragraphs. Thereafter, inspect these wing lift struts at intervals
not to exceed 24 calendar months in accordance with the
specifications presented in either paragraph (a)(1) or (a)(2) of
this AD.
(4) Install new Maule sealed wing lift struts, P/N 2200E or P/N
2201E, as applicable (or FAA-approved equivalent part numbers) on
each wing as specified in the INSTRUCTIONS section in Part II of
Maule SB No. 11, Issued: October 30, 1995.
(b) 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 paragraphs (a)(1) and (a)(2), including
all subparagraphs, of this AD.
(c) The repetitive inspections required by this AD may be
terminated after installing new wing lift strut assemblies as
specified in paragraph (a)(4) of this AD provided no holes are
drilled in these strut assemblies as specified in paragraph (b) of
this AD.
(d) Special flight permits may be issued in accordance with
sections 21.197 and 21.197 of the Federal Aviation Regulations (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
initial or repetitive compliance times that provides an equivalent
level of safety may be approved by the Manager, Atlanta Aircraft
Certification Office (ACO), One Crown Center, 1895 Phoenix
Boulevard, suite 450, Atlanta, Georgia 30349.
(1) The request shall be forwarded through an appropriate FAA
Maintenance Inspector, who may add comments and then send it to the
Manager, Atlanta ACO.
(2) Alternative methods of compliance approved in accordance
with AD 95-26-18 are considered approved as alternative methods of
compliance for this AD.
Note 5: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Atlanta ACO.
(f) All persons affected by this directive may obtain copies of
the document referred to herein upon request to Maule Aerospace
Technology, Inc., 2099 GA Hwy., 133 South, Moultrie, Georgia 31768;
or may examine this document at the FAA, Central Region, Office of
the Regional Counsel, Room 1558, 601 E. 12th Street, Kansas City,
Missouri 64106.
(g) This amendment supersedes AD 95-26-18, mendment 39-9476.
Appendix to Docket No. 98-CE-01-AD
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 accomplish
this inspection.
2. An ultrasonic probe with the following specifications will be
needed to accomplish 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
[[Page 14054]]
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 accomplish 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 the lower end of the strut as shown in
Piper Service Bulletin No. 528D or 910A, 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
[[Page 14055]]
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 Piper Service Bulletin No. 528D or 910A.
10. Record the lift strut inspection in the aircraft log book.
BILLING CODE 4910-13-U
[GRAPHIC] [TIFF OMITTED] TP24MR98.094
Issued in Kansas City, Missouri, on March 17, 1998.
Michael Gallagher,
Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. 98-7522 Filed 3-23-98; 8:45 am]
BILLING CODE 4910-13-C
