[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:

----------------------------------------------------------------------------------------------------------------
                                                                                                                
----------------------------------------------------------------------------------------------------------------
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