[Federal Register Volume 64, Number 132 (Monday, July 12, 1999)]
[Proposed Rules]
[Pages 37465-37470]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-17553]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 99-CE-13-AD]
RIN 2120-AA64
Airworthiness Directives; The New Piper Aircraft, Inc. J-2 Series
Airplanes That are Equipped With Wing Lift Struts
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed rulemaking (NPRM).
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SUMMARY: This document proposes to adopt a new airworthiness directive
(AD) that would apply to certain The New Piper Aircraft, Inc. (Piper)
J-2 series airplanes equipped with wing lift struts. The proposed AD
would require repetitively inspecting the wing lift struts for dents
and corrosion and the wing lift strut forks for cracks; replacing any
strut found with corrosion or dents, or forks with cracks; and
repetitively replacing the wing lift strut forks. The proposed AD would
also require incorporating a ``NO STEP'' placard on the lift strut. The
proposed AD is the result of the Federal Aviation Administration (FAA)
inadvertently omitting the J-2 series airplanes from the applicability
of AD 99-01-05. The actions specified by the proposed AD are intended
to prevent in-flight separation of the wing from the airplane caused by
wing lift struts with dents or corrosion or wing lift forks with
cracks, which could result in loss of control of the airplane.
DATES: Comments must be received on or before September 8, 1999.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Central Region, Office of the Regional Counsel,
Attention: Rules Docket No. 99-CE-13-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 The New Piper Aircraft, Inc., Customer Services, 2926 Piper Drive,
Vero Beach, Florida 32960. Copies of the instructions to the F. Atlee
Dodge supplemental type certificate (STC) may be obtained from F. Atlee
Dodge, Aircraft Services, Inc., P.O. Box 190409, Anchorage, Alaska
99519-0409. Copies of the instructions to the Jensen Aircraft STC's may
be obtained from Jensen
[[Page 37466]]
Aircraft, Inc., 9225 County Road 140, Salida, Colorado 81201. This
information also may be examined at the Rules Docket at the address
above.
FOR FURTHER INFORMATION CONTACT: Mr. William O. Herderich, Aerospace
Engineer, FAA, Atlanta Aircraft Certification Office, One Crown Center,
1895 Phoenix Boulevard, suite 450, Atlanta, Georgia 30349; telephone:
(770) 703-6084; 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 submitted 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. 99-CE-13-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. 99-CE-13-AD, Room 1558, 601 E. 12th Street, Kansas
City, Missouri 64106.
Discussion
AD 99-01-05, Amendment 39-10972 (63 FR 72132, December 31, 1998),
currently requires the following on certain Piper airplanes that are
equipped with wing lift struts:
--Repetitively inspecting the wing lift struts for dents and corrosion
and the wing lift strut forks for cracks; replacing any strut found
with corrosion or dents, or forks with cracks; and repetitively
replacing the wing lift strut forks;
--Incorporating a ``NO STEP'' placard on the lift strut; and
--Providing the option of installing certain wing lift strut and wing
lift strut fork assemblies, as terminating action for repetitive
inspection and replacement requirements.
AD 99-01-05 superseded AD 93-10-06, Amendment 39-8586 (58 FR 29965,
May 25, 1993). The following describes the differences between AD 93-
10-06 and AD 99-01-05:
--AD 99-01-05 clarifies certain requirements of AD 93-10-06;
--The requirement of AD 93-10-06 of repetitively inspecting the lift
strut forks on the Piper PA-25 series airplanes was deemed unnecessary
by AD 99-01-05;
--AD 99-01-05 incorporates airplane models inadvertently omitted from
AD 93-10-06;
--AD 99-01-05 requires fabricating and installing a placard on the lift
strut; and
--The J-2 series airplanes were included in the Applicability of AD 93-
10-06, but omitted from the Applicability of AD 99-01-05.
The FAA's Determination
After examining the circumstances and reviewing all available
information related to the incidents described above, the FAA has
determined that:
--The J-2 series airplanes were inadvertently omitted from AD 99-01-05;
--The actions of AD 99-01-05 should apply to the J-2 series airplanes;
and
--AD action should be taken to prevent in-flight separation of the wing
from the airplane caused by wing lift struts with dents or corrosion or
wing lift forks with cracks, which could result in loss of control of
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 Piper J-2 series airplanes of the same type
design that are equipped with wing lift struts, the FAA is proposing AD
action. The proposed AD would require repetitively inspecting the wing
lift struts for dents and corrosion and the wing lift strut forks for
cracks; replacing any strut found with corrosion or dents, or forks
with cracks; and repetitively replacing the wing lift strut forks. The
proposed AD would also require installing a placard on the lift strut,
and would provide the option of installing certain wing lift strut and
wing lift strut fork assemblies, as terminating action for repetitive
inspection and replacement requirements.
Cost Impact
The FAA estimates that 91 airplanes in the U.S. registry would be
affected by the proposed AD.
It would take approximately 8 workhours per airplane to accomplish
the proposed initial inspection, and the average labor rate is
approximately $60 an hour. Based on these figures, the total cost
impact of the proposed initial inspection on U.S. operators is
estimated to be $43,680, or $480 per airplane. These figures are based
only on the cost of the proposed initial inspection and do not take
into account the costs of any repetitive inspections. The FAA has no
way of determining how many repetitive inspections each owner/operator
would incur over the life of the airplane.
It would take approximately 4 workhours per airplane to accomplish
the proposed initial wing lift strut fork replacements, and the average
labor rate is approximately $60 an hour. Fork assemblies cost
approximately $110 each and four are required for each airplane. Based
on these figures, the total cost impact of the proposed initial wing
lift strut fork replacements on U.S. operators is estimated to be
$61,880, or $680 per airplane.
Airplane operators who do not incorporate the improved design wing
lift strut assemblies would have to repetitively replace the wing lift
strut forks. The FAA has no way of determining how many airplanes do
not have the improved design wing lift strut assemblies installed and
would need repetitive strut fork replacements.
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
[[Page 37467]]
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
part 39 of the Federal Aviation Regulations (14 CFR part 39) 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 adding a new airworthiness directive
(AD) to read as follows:
The New Piper Aircraft, Inc.: Docket No. 99-CE-13-AD.
Applicability: J-2 series airplanes, serial numbers 500 through
1975, certificated in any category; that are equipped with wing lift
struts.
Note 1: 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 (f) 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 in-flight separation of the wing from the airplane
caused by wing lift struts with dents or corrosion or wing lift
forks with cracks, which could result in loss of control of the
airplane, accomplish the following:
Note 2: 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 4: (A), (B), (C), etc.
Level 2, Level 3, and Level 4 structures are designations of the
Level 1 paragraph they immediately follow.
(a) Within 1 calendar month after the effective date of this AD
or within 24 calendar months after the last inspection accomplished
per AD 93-10-06, whichever occurs later, remove the wing lift struts
in accordance with Piper Service Bulletin (SB) No. 528D, and
accomplish one of the following (the actions in either paragraph
(a)(1), (a)(2), (a)(3), or (a)(4), including subparagraphs, of this
AD):
(1) Inspect the wing lift struts for perceptible dents (as
defined in the service bulletin referenced below) and corrosion in
accordance with the ``INSTRUCTIONS'' section in Part I of Piper SB
No. 528D, dated October 19, 1990.
(i) If no perceptible dents are found in the wing lift strut and
no corrosion is externally visible, prior to further flight, apply
corrosion inhibitor to each strut in accordance with the SB
referenced above. Reinspect the lift struts at intervals not to
exceed 24 calendar months.
(ii) If a perceptible dent 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) or (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 inspector certified using
the guidelines established by the American Society for Non-
destructive Testing, or MIL-STD-410.
(i) If no corrosion is found that is externally visible and all
requirements in the Appendix to this AD are met, prior to further
flight, apply corrosion inhibitor to each strut in accordance with
the SB referenced above. Reinspect the lift struts at intervals not
to exceed 24 calendar months.
(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)
or (a)(4) of this AD.
(3) Install original equipment manufacturer (OEM) part number
wing 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 sealed wing lift strut assemblies, part numbers
as specified in Piper SB No. 528D (or FAA-approved equivalent part
numbers), on each wing as specified in the INSTRUCTIONS section in
Part II of the above-referenced SB. These sealed wing lift strut
assemblies also include the wing lift strut forks. Installation of
these assemblies constitutes terminating action for the inspection
and replacement requirements of both paragraphs (a) and (b) of this
AD.
(b) Within the next 100 hours time-in-service (TIS) after the
effective date of this AD or within 500 hours TIS after the last
inspection, whichever is later, remove the wing lift strut forks and
accomplish one of the following (the actions in either paragraph
(b)(1), (b)(2) or (b)(3); including subparagraphs, of this AD):
(1) Inspect the wing lift strut forks for cracks using FAA-
approved magnetic particle procedures.
(i) If no cracks are found, reinspect at intervals not to exceed
500 hours TIS provided that the replacement requirements of
paragraphs (b)(1)(ii)(B) and (b)(1)(ii)(C) of this AD have been met.
(ii) Replace the wing lift strut forks at whichever of the
following is applicable:
(A) If cracks are found on any wing lift strut fork: Prior to
further flight;
(B) If the airplane is equipped with floats or has been equipped
with floats within the last 2,000 hours TIS and no cracks are found
during the above inspections: Upon accumulating 1,000 hours TIS on
the wing lift strut forks or within the next 100 hours TIS after the
effective date of this AD, whichever occurs later; or
(C) If the airplane has not been equipped with floats within the
last 2,000 hours TIS and no cracks are found during the above
inspections: Upon accumulating 2,000 hours TIS on the wing lift
strut forks or within the next 100 hours TIS after the effective
date of this AD, whichever occurs later.
(iii) Replacement parts shall be of the same part numbers of the
existing part (or FAA-approved equivalent part numbers) and shall be
manufactured with rolled threads. Lift strut forks manufactured with
machined (cut) threads shall not be utilized.
(iv) The 500-hour TIS interval repetitive inspections are still
required when the above replacements are accomplished.
(2) Install new OEM part number wing lift strut forks (or FAA-
approved equivalent part numbers). Reinspect and replace these wing
lift strut forks at the intervals specified in paragraphs (b)(1)(i),
(b)(1)(ii), (b)(1)(iii), and (b)(1)(iv), including all
subparagraphs, of this AD.
(3) Install new sealed wing lift strut assemblies, part numbers
as specified in Piper SB No. 528D (or FAA-approved equivalent part
numbers), on each wing as specified in the INSTRUCTIONS section in
Part II of the above-referenced SB.
(i) This installation may have ``already been accomplished''
through the actions specified in paragraph (a)(4) of this AD.
(ii) No repetitive inspections are required after installing
these sealed wing lift strut assemblies.
(c) If holes are drilled in wing lift strut assemblies installed
in accordance with (a)(4) or (b)(3) of this AD 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) or (a)(2), including all subparagraphs, of this
AD.
(d) Within 1 calendar month after the effective date of this AD
and thereafter prior
[[Page 37468]]
to further flight after the installation of any lift strut assembly,
accomplish one of the following:
(1) Install ``NO STEP'' decal, Piper part number (P/N) 80944-02,
on each wing lift strut approximately 6 inches from the bottom of
the struts in a way that the letters can be read when entering and
exiting the aircraft; or
(2) Paint the statement ``NO STEP'' approximately 6 inches from
the bottom of the struts in a way that the letters can be read when
entering and exiting the aircraft. Use a minimum of 1-inch letters
utilizing a color that contrasts with the color of the airplane.
(e) Special flight permits may be issued in accordance with
sections 21.197 and 21.199 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.
(f) An alternative method of compliance or adjustment of the
initial and repetitive compliance times that provides an equivalent
level of safety may be approved by the Manager, FAA, Atlanta
Aircraft Certification Office (ACO), One Crown Center, 1895 Phoenix
Boulevard, suite 450, Atlanta, Georgia 30349. The request shall be
forwarded through an appropriate FAA Maintenance Inspector, who may
add comments and then send it to the Manager, Atlanta ACO.
Note 3: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Atlanta ACO.
(g) The service bulletins referenced in this AD may be obtained
from The New Piper Aircraft, Inc., Customer Services, 2926 Piper
Drive, Vero Beach, Florida 32960. Copies of the instructions to the
Jensen Aircraft STC's may be obtained from Jensen Aircraft, 9225
County Road 140, Salida, Colorado 81201. Copies of the instructions
to the F. Atlee Dodge STC may be obtained from F. Atlee Dodge,
Aircraft Services, Inc., P.O. Box 190409, Anchorage, Alaska 99519-
0409. These documents may be examined at the FAA, Central Region,
Office of the Regional Counsel, Room 1558, 601 E. 12th Street,
Kansas City, Missouri.
Appendix to Docket No. 99-CE-13-AD; Procedures and Requirements for
Ultrasonic Inspection of Piper 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 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.
[[Page 37469]]
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 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-P
[[Page 37470]]
[GRAPHIC] [TIFF OMITTED] TP12JY99.032
Issued in Kansas City, Missouri, on July 2, 1999.
Marvin R. Nuss,
Acting Manager, Small Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 99-17553 Filed 7-9-99; 8:45 am]
BILLING CODE 4910-13-C
