Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 1 of 23

SERVICE BULLETIN

SA226 SERIES

FUSELAGE

Inspection and/or Replacement of the Left Hand and Right Hand Forward and Aft

Wing-to-Body Attach Fittings.

1. PLANNING INFORMATION

A. Effectivity:

All SA226-T/-T(B)/-TC/-AT Airplanes.

B. Reason:

To provide operators with instructions for the inspection and /or replacement of the left

hand and right hand forward and aft spar wing-to-body attach fittings.

This revision corrects steps 1.B., 1.D, 1.F., 1.G.(2), 1.H., 2.A.(2), 2.A.(3), 2.A.(7),

2.A.(8), 2.F.(2), 2.G.(1), 2.G.(1)(b), 2.G.(1)(c), 2.G.(1)(f), 2.G.(1) (j), 2.G.(1)(m), 2.G.(1)(n),

2.G.(1)(o), 2.G.(1)(p)1, 2.G.(1)(p)2, 2.G.(1)(p)3, 2.G.(1)(p)4, 2.G.(1)(p)5, 2.G.(1)(q),

2.G.(1)(r), 2.G.(1)(s), 2.G.(1)(t), 2.G.(2)(b), 2.G.(2)(c), 2.G.(2)(f), 2.G.(2)(l), 2.G.(2)(n),

2.G.(2)(o), 2.G.(2)(p), 2.G.(2)(q)1, 2.G.(2)(q)2, 2.G.(2)(q)3, 2.G.(2)(q)4, 2.G.(2)(q)5,

2.G.(2)(r), 2.G.(2)(s), 2.G.(2)(t), 2.G.(2)(u), 2.H.(1), 2.H.(7), Table 1, Table 2, Table 3,

Table 4, and Figures 3, 4, and 5. All changes are denoted by a black revision bar in the

left margin.

Compliance with previous (IR) version of this service bulletin is satisfactory as

compliance for this revision except if aircraft serial numbers fall within range specified

by Figure 5, Note 4. See step 1.D. for specific compliance with this Note 4.

C. Description:

Inspect the left hand and right hand forward and aft spar wing-to-body attach fittings for

cracks. If cracks are found, replace fitting(s).

D. Compliance:

Highly Recommended

For aircraft with more than 35,000 Total Aircraft Cycles (TAC), inspect within next 300

cycles from the date of this service bulletin.

For aircraft with 20,000 - 35,000 Total Aircraft Cycles (TAC), inspect within next 500

cycles from the date of this service bulletin.

For aircraft with 10,600 - 19,999 Total Aircraft Cycles (TAC), inspect within next 1,000

cycles from the date of this service bulletin.

For aircraft with less than 10,600 Total Aircraft Cycles (TAC), inspect at 10,600 cycles

or within the next 1,000 cycles, whichever occurs later.
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 2 of 23

SERVICE BULLETIN

SA226 SERIES

For aircraft which have been inspected per initial issue (July 27, 2012) of this bulletin

and those serial numbers that fall within the range specified in Figure 5, Note 4, and had

the doubler cutout trimmed per Notes 1 and 2, the addition of the straps must be

complied with within the next 2,000 cycles/2,000 hours, whichever occurs first, unless

this has already been accomplished. This interval is specified from when the trim per

Figure 5, Note 1 was undertaken.

TABLE 1

E. Approval:

FAA Approved for Engineering Design.

F. Manpower:

The M7 Aerospace manhour estimate for this service bulletin is as follows:

(1) 180 hours for access, including removing interior, floorboards in the area,

removing structure adjacent to fittings, and removing sealant for NDT inspection.

(2) 6 hours for NDT inspection of all 8 fittings at 4 locations.

(3) 170 hours for replacement of one pair of fittings at the front spar, and 100 hours

for replacement of one pair of fittings at the rear spar.

 This estimate is for direct labor only, accomplished by an experienced crew. Adjust the

estimate with operator task-hour data if necessary.

G. Material – Cost and Availability:

(1) Cost:

Because of pricing fluctuations, individual cost estimates should be obtained

from your normal material procurement outlet.

SA226-T/-T(B)/-AT/-TC, ALL 

Fittings Installed with 

Nominal/Original 

Factory Bolts

Original Fitting 10,600 Cycles

Fittings Installed 

with 1 or more 

Oversized Bolts

Replacement Fitting 16,600 Cycles

7,700 Cycles

13,100 Cycles

 Aircraft Cycles Until Recurrent Inspection
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 3 of 23

SERVICE BULLETIN

SA226 SERIES

Additional material cost information may be contained in the Index or the

Letter of Transmittal.

(2) Availability:

Contact M7 Aerospace Spares/Sales for parts availability.

H. Tooling – Price and Availability:

For tools/kits identified in Supplement A of this service bulletin, contact Perimeter

Aviation NDT department, ph 204-791-9848, fax 204-480-4025.

I. Weight and Balance:

Negligible

NOTE: It is recommended the aircraft operating weight be reestablished after incorporating 20 service bulletins classified as having 'negligible' impact on aircraft

weight and balance. This recommendation is derived from data provided in

FAA Advisory Circular 120-27.

J. References:

SA226/227 Structural Repair Manual.

SA226 Maintenance Manual.

NOTE: References are for manufacturer’s use only.

K. Other Publications Affected:

SA226 Maintenance Manual.

SA226 Airframe Inspection Manual, ST-UN-M002

SA226/227 Supplemental Inspection Document (SID)

2. ACCOMPLISHMENT INSTRUCTIONS

The four (4) fastener locations fastening the Main (Fwd) spar wing-to-fuselage fittings to the

spar must be inspected for cracks. Two inspection methods are permissible. A method has

been developed to ultrasonically inspect the fittings without removing the fasteners, provided

that there is adequate clearance between fastener head and wall of fitting for the tranducer

head. Alternately, the fasteners can be removed and the open bore holes inspected using High

Frequency Eddy Current (HFEC). The latter method requires additional labor hours and

aircraft access.

Access requirements are detailed in step 2.A. Inspection methods are detailed in steps 2.B.

and 2.C.
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 4 of 23

SERVICE BULLETIN

SA226 SERIES

A. Access

(1) Remove electrical power from aircraft. Turn off main batteries. Ensure GPU is not

connected to aircraft. Tag out circuit breakers and battery switches to prevent

injury to personnel or damage to the aircraft.

(2) Remove interior furnishings, cabin seats, carpet, floorboards, and side panels as

required to gain access to wing carry-thru area from inside the fuselage. Removal

of the outboard seat track beam may be required. Contact M7 Aerospace for

further support if needed.

(3) Gain access to wing-to-fuselage mount fittings, P/N 27-22121 and 27-22123 at

main spar, P/N 27-22135 and 27-22136 at aft spar.

(a) Access to the aft spar fitting inspection area (see step 2.E.) may be possible from

outside the aircraft with the wing-to-fuselage fairing removed. Access is dependent on skin trim at the spar cutout, which varies.

(b) If accessing aft spar fitting from inside, remove 27-30004 seal at skin cutout for

fitting (between aft spar frames). Retain fasteners for size and type.

(4) At the main spar, remove sealant around the heads of the four fasteners in the

base of the fittings (attached to upper spar cap) as necessary to allow inspection

per steps 2.B., 2.C., and 2.D. (See Figure 1)

(5) At the main and aft spars, remove sealant obscuring the upper outboard fillet radii

as necessary to allow inspection per 2.B., 2.C., and 2.D. (See Figure 1)

If the fastener bore eddy current inspection method is used (see step 2.B.), continue

with steps (6) through (14). Otherwise go to step 2.C.

(6) Defuel aircraft and sump fuel in accordance with SA226 Maintenance Manual 12-

30-15.

(7) Lift and shore aircraft per SA226 Maintenance Manual 07-10-00. Use fuselage

and wing cradles. Contact M7 Aerospace for further details if required.

(8) Remove wing belly skins and wing-to-fuselage fairings from WS 27 RH to WS 27

LH fore and aft of the main spar. Note size and type of fasteners for reinstallation.

Removal of wing belly skins may not be necessary but will give additional access

if required.

(9) Remove accessories, plumbing, and equipment as required for access to the

main spar pressure plate outboard (approx. BL 22) access panels.
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 5 of 23

SERVICE BULLETIN

SA226 SERIES

(10) Remove front and aft side main pressure plate access panels.

(11) Remove forward collector tank access panel in WS 27 rib web and upper collector

tank baffle.

(12) Remove under wing access panel, forward of spar and immediately outboard of

WS 27.

(13) Remove air conditioning duct valve, anti-ice valve, and water separator inside

under-wing access panel. Bag and tag ends of tubes and parts for reinstallation.

(14) Remove inboard and outboard tension bolts through spar cap from main spar

forward and aft fitting halves (see Figure 1). The fasteners will be replaced with

new hardware.

NOTE: Fastener heads may be ground off to facilitate removal. Take care not to

damage fitting. Before punching fasteners through into the spar and wing

interor, check to ensure clearance with other fasteners through spar and

WS 27 rib webs below. Remove other fasteners as necessary to avoid

damage. For repair of damaged holes, see step 3. of this bulletin.

B. Main spar fitting fastener bore eddy current inspection

At the main spar LH and RH wing-to-fuselage fittings (see Figure 2 for probable crack

locations):

(1) High Frequency Eddy Current (HFEC) inspect the inside diameter of the open bolt

holes in the wing-to-fuselage fittings per SA226/227 Structural Repair Manual

(SRM) 51-30-07.

(2) Proceed to step 2.D.

C. Main spar fitting endpad ultrasonic inspection

At the main spar LH and RH wing-to-fuselage fittings:

(1) Using the method detailed in Supplement A to this service bulletin for aircraft

listed in Table 3, inspect the endpad fitting surface around the heads of the four

tension bolt fasteners. See Figure 2 for probable crack locations. If unable to use

this method as outlined in Supplement A, step 7 Note, then method per step 2.B.

shall be used.

D. Main spar fitting radii inspection

At the main spar LH & RH wing-to-fuselage fittings:

(1) High Frequency Eddy Current (HFEC) inspect per SA226/227 Structural Repair

Manual 51-30-07 the upper edge of the inboard gusset on both fitting halves. See

Figure 2 for probable crack locations.
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 6 of 23

SERVICE BULLETIN

SA226 SERIES

(2) High Frequency Eddy Current (HFEC) inspect per SA226/227 Structural Repair

Manual 51-30-07 in the fillet radii of the upper outboard corner on both fitting

halves. See Figure 2 for probable crack locations.

NOTE: There is one further inspection required if the main spar fittings are removed

and replaced. See steps G.(1)(l).

E. Aft spar fitting inspection

(1) At the aft spar LH and RH wing-to-fuselage fittings inspect for cracks in the fillet

radii of the upper outboard corner on both fitting halves using High Frequency

Eddy Current methods in accordance with SA226/227 Structural Repair Manual

(SRM) 51-30-07.

F. Disposition

(1) If a crack is found in any one of the fitting halves, remove and replace both fitting

halves. See step G. for removal instructions. See step K. for reporting instructions.

(2) If hardware was removed at the main spar fitting and no crack indications were

found, wet install new hardware per SA226/227 Structural Repair Manual (SRM)

51-30-03.

Inboard Bolts

MS20005-25 Bolt,

MS20002C5 Washer,

52LH4367-054 Nut,

4367-05 Washer

Outboard Bolts

MS20005-23 Bolt,

MS20002C5 Washer,

52LH4367-054 Nut,

4367-05 Washer

NOTE: Grip length of fasteners may vary depending on structure and sealant build

up at each fastener location. Measure each location to ensure proper length.

(3) Torque bolts to 190 - 220 in-lbs in accordance with SA226/227 Structural Repair

Manual (SRM) 51-40-07 using a cross sequence tightening schedule (e.g., 12

o'clock to 6 o'clock, 3 o'clock to 9 o'clock, 12:05 o'clock to 6:05 o'clock, etc.).

(4) Reseal the area where sealant was removed earlier and overcoat nuts in wet fuel

tank per SA226/227 Structural Repair Manual (SRM) 51-30-03.
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 7 of 23

SERVICE BULLETIN

SA226 SERIES

G. Removal and Replacement

Remove and replace both fitting halves at any location where cracks are found.

(1) Main Spar Fittings

If bolts have already been removed from fitting for bolt hole inspection, skip to step

2.G.(1)(j).

(a) Defuel aircraft and sump fuel in accordance with SA226 Maintenance Manual

12-30-15.

(b) Lift and shore aircraft in accordance with SA226 Maintenance Manual 07-10-00.

Use fuselage and wing cradles. Contact M7 for further information if required.

(c) Remove wing belly skins and wing-to-fuselage fairings fore and aft of the main

spar to gain access if required. Note size and type of fasteners for reinstallation.

(d) Remove accessories, plumbing, and equipment as required for access to the

main spar pressure plate outboard (approx. BL 22) access panels.

(e) Remove front and aft side main pressure plate access panels.

(f) Remove under-wing boost pump access panel. Remove boost pumps and

plumbing as required for access to aft outboard fitting attach fastener.

(g) Remove under wing access panel, forward of spar and immediately outboard of

WS 27.

(h) Remove air conditioning duct valve, anti-ice valve, and water separator inside

under-wing access panel. Bag and tag ends of tubes and parts for reinstallation.

(i) Remove fitting hardware through spar cap. (Refer to step 2.(A)(14)).

(j) Remove fitting hardware through fuselage frame webs and retain for size and

type.

(k) Remove 27-22118 Mount Assembly. Permissible to trim 27-22025 Doubler on

inner frame cap in accordance with Figure 5 if necessary to remove Mount Assy.

Retain shims between frame and fittings noting orientation and location for later

installation.

(l) High frequency Eddy Current (HFEC) inspect the inside diameter of the open bolt

holes (4) in the titanium upper spar cap per SA226/227 Structural Repair Manual

(SRM) 51-30-07. Contact M7 Engineering if a crack is found.

(m) Build a tooling fixture to capture locations and hole alignment of holes in spar cap.
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 8 of 23

SERVICE BULLETIN

SA226 SERIES

(n) Duplicate holes from fixture to new fitting halves. Hole size 0.312/0.316" diameter. Deburr. Drill holes per SA226/227 Structural Repair Manual (SRM) 51-40-

07.

(o) Assemble the 27-22121 and 27-22123 fitting halves loosely to form the 27-22118

Mount Assembly (Figure 3). Do not pick up holes in fittings from splice plate until

fittings are located following the next step.

(p) Install mount assembly in accordance with the following installation notes:

1 Ensure all four spar bolt holes are aligned through all components in stack-up.

2 Permissible to remove 0.060" material locally from underside of base of mount

assy to match irregularities of mating spar caps. Fittings must maintain

minimum base thickness of 0.290". Alodine and prime any reworked surfaces

and bare edges per SA226/227 Structural Repair Manual (SRM) 51-30-02.

Ensure that more than one-half of forward and aft edge of mount assy is in

contact with spar caps. Max allowable remaining gap is 0.020". Fill remaining

gaps with Devcon-F per step 2.G.(1)(p)3.

3 Apply Devcon-F (putty type) between mating surfaces of mount assy and spar

to fill any existing gaps less than 0.020" after mount assy is made to contact

spar cap along more than half of both fwd and aft edges. Prior to application

of Devcon-F, clean and treat mating surfaces with Devcon release agent.

4 Replace bolts and wet install per SA226/227 Structural Repair Manual (SRM)

51-30-03 through spar cap:

Inboard Bolts

MS20005-25 Bolt,

MS20002C5 Washer,

52LH4367-054 Nut,

4367-05 Washer

Outboard Bolts

MS20005-23 Bolt,

MS20002C5 Washer,

52LH4367-054 Nut,

4367-05 Washer

NOTE: Grip length of fasteners may vary depending on structure and sealant

build up at each fastener location. Measure each location to ensure

proper length.

5 Torque MS20005 bolts through spar cap to 190 - 220 in-lbs in accordance with
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 9 of 23

SERVICE BULLETIN

SA226 SERIES

SA226/227 Structural Repair Manual (SRM) 51-40-07 using a cross sequence tightening schedule (e.g., 12 o'clock to 6 o'clock, 3 o'clock to 9 o'clock,

12:05 o'clock to 6:05 o'clock, etc.). Overcoat all nuts in fuel tank with sealant

per SA226/227 Structural Repair Manual (SRM) 51-30-03.

(q) Pick up existing fastener holes through frame webs. Hole size 0.190/0.194"

diameter. Reinstall any shims between frame web and fittings that were existing

in same location/orientation as previous. Shims shall be fay surface sealed per

SA226/227 Structural Repair Manual (SRM) 51-30-03. Contact M7 Aerospace

if new shims are required (see Note 4, Figures 3 and 4). Install new existing type

(NAS1103) fasteners or install new NAS6203-( ) Bolt, NAS1149F0332P Washer

(or any other NAS1149 cad-plated), and MS21042L3 Nut. Install fasteners per

SA226/227 Structural Repair Manual (SRM) 51-40-07.

(r) Pick up existing fastener holes through 27-31264 Support Clips. Maintain

fastener type and size. Install fasteners per SA226/227 Structural Repair Manual

(SRM) 51-40-07.

(s) Pick up existing holes through the 27-22124 splice plate(s). Maintain 2D edge

distance on new fittings. Install fasteners per SA226/227 Structural Repair

Manual (SRM) 51-40-07. Fay surface seal the splice plates per SA226/227

Structural Repair Manual (SRM) 51-30-03. See Figure 3 for fastener type and

hole size.

(t) M7 Aerospace recommends to install new hardware for all locations that hardware was removed for this modification.

(2) Aft Spar Fittings

(a) Defuel aircraft and sump fuel in accordance with SA226 Maintenance Manual

12-30-15.

(b) Lift and shore aircraft in accordance with SA226 Maintenance Manual 07-10-00.

Use fuselage and wing cradles. Contact M7 Aerospace for further information if

required.

(c) Remove wing belly skins and wing-to-fuselage fairings fore and aft of the aft spar

as required for access. Note size and type of fasteners for reinstallation.

(d) Remove accessories, plumbing, and equipment as required for access to the aft

spar pressure plate outboard (approx. BL 22) access panels.

(e) Remove front and aft side aft spar pressure plate access panels.

(f) Remove under-wing boost pump access panel. Remove boost pumps and

plumbing as required for access to forward outboard fitting attach fastener.

(g) Remove 27-71003 or 27-19097 Tube Assy (aileron control system).
Issued: July 27, 2012

Revised: May 13, 2013

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Page 10 of 23

SERVICE BULLETIN

SA226 SERIES

(h) Remove flap walking beam.

(i) Remove flap.

(j) Remove or secure inboard flap hinge linkage parts to allow clear access to nut

side of aft, outboard fitting bolt.

(k) Remove fitting hardware through spar cap. (Refer to step 2.(A)(14) NOTE, apply

to aft spar).

(l) Remove fitting hardware through fuselage frame webs and retain for size and

type.

(m) Remove 27-22119 Mount Assy. Permissible to trim 27-22025 Doubler on inner

frame cap in accordance with Figure 5 if necessary to remove Mount Assy. Retain

shims between frame and fittings noting orientation and location for later installation.

(n) Build a tooling fixture to capture locations and hole alignment of holes in spar cap.

(o) Duplicate holes from fixture to new fitting halves. Hole size 0.250/0.254" diameter. Deburr. Drill holes per SA226/227 Structural Repair Manual (SRM) 51-40-

07.

(p) Assemble the 27-22135 and 27-22136 fitting halves loosely to form the 27-22119

Mount Assembly (Figure 4). Do not pick up holes in fittings from 27-22137 splice

until fittings are located following the next step.

(q) Install mount assembly in accordance with the following installation notes:

1 Ensure all four spar bolt holes are aligned through all components in stack-up.

2 Permissible to remove 0.060" material locally from underside of base of mount

assy to match irregularities of mating spar caps. Fittings must maintain

minimum base thickness of 0.290". Alodine and prime any reworked surfaces

and bare edges per SA226/227 Structural Repair Manual (SRM) 51-30-02.

Ensure that more than one-half of forward and aft edge of mount assy is in

contact with spar caps. Max allowable remaining gap is 0.020". Fill remaining

gaps with Devcon-F per step 2.G.(2)(q)3.

3 Apply Devcon-F (putty type) between mating surfaces of mount assy and spar

to fill any existing gaps less than 0.020" after mount assy is made to contact

spar cap along more than half of both fwd and aft edges. Prior to application

of Devcon-F, clean and treat mating surfaces with Devcon release agent.

4 Replace 4 bolts and wet install per SA226/227 Structural Repair Manual

(SRM) 51-30-03 through spar cap:
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SERVICE BULLETIN

SA226 SERIES

MS20004-22 Bolt, Aft, Outbd & Inbd

MS20004-24 Bolt, Fwd, Outbd

MS20004-26 Bolt, Fwd, Inbd

MS20002C4 Washer,

52LH4367-048 Nut,

RM2935-04 Washer

NOTE: Grip length of fasteners may vary depending on structure and sealant

build up at each fastener location. Measure each location to ensure

proper length.

5 Torque MS20004 bolts through spar cap to 100 - 140 in-lbs in accordance with

SA226/227 Structural Repair Manual (SRM) 51-40-07 using a cross sequence tightening schedule (e.g., 12 o'clock to 6 o'clock, 3 o'clock to 9 o'clock,

12:05 o'clock to 6:05 o'clock, etc.). Overcoat all nuts in fuel tank with sealant

per SA226/227 Structural Repair Manual (SRM) 51-30-03.

(r) Pick up existing fastener holes through frame webs. Hole size 0.190/0.194"

diameter. Reinstall any shims between frame web and fittings that were existing

in same location/orientation as previous. Shims shall be fay surface sealed per

SA226/227 Structural Repair Manual (SRM) 51-30-03. Contact M7 Aerospace

if new shims are required (see Note 4, Figures 3 and 4). Install new existing type

(NAS1103) fasteners or install new NAS6203-( ) Bolt, NAS1149F0332P Washer

(or any other NAS1149 cad-plated), and MS21042L3 Nut. Install fasteners per

SA226/227 Structural Repair Manual (SRM) 51-40-07.

(s) Pick up existing fastener holes through 27-30000-087/-088 Bracket on fwd side.

Maintain fastener type and size. Install fasteners per SA226/227 Structural

Repair Manual (SRM) 51-40-07.

(t) Pick up existing holes through the 27-22137 splice plate(s). Maintain 2D edge

distance on new fittings. Install fasteners per SA226/227 Structural Repair

Manual (SRM) 51-40-07. Fay surface seal the splice plates per SA226/227

Structural Repair Manual (SRM) 51-30-03. See Figure 4 for fastener type and

hole size.

(u) M7 Aerospace recommends to install new hardware for all locations that hardware was removed for this modification.

H. Close Up

(1) Reinstall any fasteners through the spar web or WS 27 rib web that were removed

to facilitate removal of fitting tension bolts through spar cap. Install same type and

size in accordance with SA226/227 Structural Repair Manual (SRM) 51-40-07.

(2) Ensure area is fillet sealed and overcoat fasteners in wet fuel tank per SA226/227

Structural Repair Manual (SRM) 51-30-03.
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SERVICE BULLETIN

SA226 SERIES

(3) Restore collector tank, reseal fasteners, and close collector tank access panel.

(4) Reinstall spar access panels and center section equipment and systems per

applicable sections of the SA226 Maintenance Manual.

(5) Reinstall air conditioning duct valve, anti-ice valve, and water separator and

reinstall under-wing access panel.

(6) Remove shoring.

(7) Refuel aircraft and check for leaks. Refer to SA226 Maintenance Manual, Chapter

28-10-10.

(8) Reinstall wing-to-fuselage fairing and interior parts and components per applicable sections of the SA226 Maintenance Manual.

(9) If aft spar fittings were replaced, continue through step H.(12). Otherwise proceed

to step 2.I.

(10) Reinstall flap and flap walking beam.

(11) Reinstall 27-71003 or 27-19097 Tube Assy (aileron control system).

(12) Remove tags from battery switches and circuit breakers pulled in step 2.A.(1).

Connect GPU to aircraft.

(13) Perform aileron control system operational checks in accordance with SA226

Maintenance Manual 27-10-10.

(14) Perform flap control system operational checks in accordance with SA226

Maintenance Manual 27-50-10.

I. Complete maintenance entry per 14 CFR 43.9.

J. Complete and return Service Bulletin Compliance Form to M7 Aerospace Technical

Publications.

K. Reporting requirements

Damage reporting is required to ensure compliance times are validated. If a crack

is found at any location, the following information needs to be relayed to M7

Engineering as soon as possible.

(1) State length of crack and a general description of the damage.

(2) State aircraft model, serial number, aircraft total flight cycles and total flight hours.

(3) Using Figure 2, indicate location of damage, show forward orientation using

arrows, and orientation of crack.
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SA226 SERIES

(4) State whether the aircraft has had or is suspected of having a hard landing in the

past.

(5) Send this information to M7 Technical Support at MetroTech@M7Aerospace.com

or (210)-824-9421, ext. 7294.

3. REPAIR OF DAMAGED FASTENER HOLES

Damaged fastener holes in the base of the fitting and spar cap (fasteners attaching the fitting

to the spar cap) may be repaired within the following parameters.

A. Holes may be enlarged for the first oversize, second oversize, or the next full size

fastener. (See Table 2)

B. Torque settings for fastener installation. Refer to SA226/227 Structural Repair

Manual (SRM) 51-40-07 for guidance. Torque fasteners using a cross sequence

tightening schedule (e.g., 12 o'clock to 6 o'clock, 3 o'clock to 9 o'clock, 12:05

o'clock to 6:05 o'clock, etc.).

(1) 1/4 in. nut 100 - 140 in-lbs.

(2) 5/16 in. nut 190 - 220 in-lbs.

(3) 3/8 in. nut 220 - 360 in-lbs.

C. Washers under heads of fasteners may be trimmed or chamfered to avoid

interference with fitting fillet radii. Maintain a full bearing surface for the head of the

fastener.

D. If a 3/8 in. diameter fastener is used in any main spar inboard location, then all four

fasteners at this fitting location must be increased to 3/8 in. diameter. (See Table 2)
Issued: July 27, 2012

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SERVICE BULLETIN

SA226 SERIES

NOTE: Grip length of fasteners may vary depending on structure and sealant build

up at each fastener location. Measure each location to ensure proper length.

TABLE 2

Oversize Hardware for Hole Repair *

Main Spar Inbd Main Spar Outbd Aft Spar, Aft Fitting

1st

Oversize

(0.0156)

0.332/0.328 Dia. Hole

NAS6205-25X Bolt 

NAS1149F0563P Washer

52LH4367-054 Nut

4367-05 Washer

* If this fastener is too close to the fitting gusset to permit proper installation, a radius block

 of sufficient thickness to lift the head or nut above the gusset may be employed. Create radius 

 block from 2024-T3 per AMS-QQ-A-250/4. Size to be no less than washer diameter. Max

 thickness = 0.30 inches. Machine radius to match fitting fillet radius. Finish in accordance 

 with SA226/227 Structural Repair Manual (SRM) 51-30-02. Adjust fastener length accordingly.

0.332/0.328 Dia. Hole

NAS6205-23X Bolt 

NAS1149F0563P Washer

52LH4367-054 Nut

4367-05 Washer

0.266/0.270 Dia. Hole

NAS6204-22X Bolt 

NAS1149F0463P Washer

52LH4367-048 Nut

RM2935-04 Washer

0.348/0.344 Dia. Hole

NAS6205-25Y Bolt 

NAS1149F0663P Washer

52LH4367-054 Nut

4367-05 Washer

0.348/0.344 Dia. Hole

NAS6205-23Y Bolt 

NAS1149F0663P Washer

52LH4367-054 Nut

4367-05 Washer

0.285/0.281 Dia. Hole

NAS6204-22Y Bolt 

NAS1149F0563P Washer

52LH4367-048 Nut

RM2935-04 Washer

2nd

Oversize

(0.0312)

0.379/0.375 Dia. Hole

MS20006-25 Bolt 

MS20002C6 Washer

52LH4367-064 Nut

4367-06 Washer

See step 3.D. 

Next Size

0.379/0.375 Dia. Hole

MS20006-23 Bolt 

MS20002C6 Washer

52LH4367-064 Nut

4367-06 Washer

0.316/0.312 Dia. Hole

MS20005-22 Bolt 

MS20002C5 Washer

52LH4367-054 Nut

4367-05 Washer

Aft Spar, Fwd Fitting

0.266/0.270 Dia. Hole

NAS6204-24X Bolt (Outbd)

NAS6204-26X Bolt (Inbd)

NAS1149F0463P Washer

52LH4367-048 Nut

RM2935-04 Washer

0.285/0.281 Dia. Hole

NAS6204-24Y Bolt (Outbd)

NAS6204-26Y Bolt (Inbd)

NAS1149F0563P Washer

52LH4367-048 Nut

RM2935-04 Washer

0.316/0.312 Dia. Hole

MS20005-24 Bolt (Outbd)

MS20005-26 Bolt (Inbd)

MS20002C5 Washer

52LH4367-054 Nut

4367-05 Washer
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 15 of 23

SERVICE BULLETIN

SA226 SERIES

4. MATERIAL LISTING

TABLE 3

Replacement Wing-to-Fuselage Attach Fitting Part Numbers <1>

Aircraft Model Serial Number Main Spar Aft Spar

27-22121

Fwd Half

27-22123

Aft Half

SA226-T

SA226-T(B)

SA226-TC

SA226-AT

201 - 291

276 - 324

201 - 320

001 - 074

-013/-014 -013/-014 -007/-008 -007/-008

SA226-T(B)

SA226-TC

325 - 391

321 - 396 -015/-016 -015/-016 -007/-008 -007/-008

SA226-T(B)

SA226-TC

394 - 417

398 - 419

-019/-020 -019/-020 -007/-008 -007/-008

27-22135

Fwd Half

27-22136

Aft Half

<1> New replacements have recurring inspections per Table 1 since 

 installation. This bulletin shall be used to detail inspections and 

 instructions.
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 16 of 23

SERVICE BULLETIN

SA226 SERIES

For Table NOTES, see page 17.

TABLE 4

Fitting-to-Spar Hardware and Alternates

Location Existing Alternate 1

Main Spar

Inboard

MS20005-25 Bolt MS21250-05025 Bolt 2

MS20002C5 Washer

52LH4367-054 Nut

4367-05 Washer

NAS1727-5 Nut &

Washer Combo 3

Main Spar

Outboard

MS20005-23 Bolt

MS20002C5 Washer

52LH4367-054 Nut

4367-05 Washer

MS21250-05023 Bolt 2

NAS1727-5 Nut &

Washer Combo 3

Aft Spar,

Aft Side

MS20004-22 Bolt MS21250-04022 Bolt 2

MS20002C4 Washer

52LH4367-048 Nut NAS1727-4 Nut &

Washer Combo 3 RM2935-04 Washer

Aft Spar,

Fwd Side

MS20004-24 Bolt (Outbd)

MS20004-26 Bolt (Inbd)

MS20002C4 Washer

52LH4367-048 Nut

RM2935-04 Washer

MS21250-04024 Bolt 2

MS21250-04026 Bolt 2

NAS1727-4 Nut &

Washer Combo 3 

Fitting-to-Frame Hardware and Alternates

Location Existing Alternate 

All Locations LH7559-3 Nut MS21042L3 Nut

All Locations

NAS1303 Nut

NAS1304 Nut

NAS1103 Nut

NAS6603 Nut

NAS6604 Nut

NA6203 Nut
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 17 of 23

SERVICE BULLETIN

SA226 SERIES

TABLE 4 NOTES

Notes:

1. Alternate parts vary in size from existing parts and may not fit 

 depending on fastener location.

2. The four fasteners at one location must be of the same type. The 

 four fasteners must be substituted together. 

3. The NAS1727-4/-5 nuts a physically larger than the original 

 nut/washer combination. This may result in requiring a longer grip 

 length bolt to ensure correct safety on the bolt. See NOTE * in 

 Table 2 for use of radius block if required.

4. Grip lengths of fasteners may vary depending on local conditions. 

 Measure at each location to ensure proper length.
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 18 of 23

SERVICE BULLETIN

SA226 SERIES

FIGURE 1

B

B

Note 2

(2 Places)

A

A

Note 2

(2 Places)

Note 1

(4 Places)

Notes: 

 1. Remove sealant from around 4 fastener heads in base of fittings.

 2. Remove sealant in fillet radius at upper edge and approximately 1 inch along inside

 vertical corner.

 3. For inspection per 2.B., remove inboard and outboard bolts in both fitting halves. 

Note 3

Aft Spar Fitting

Main Spar Fitting
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 19 of 23

SERVICE BULLETIN

SA226 SERIES

PROBABLE CRACK LOCATIONS

FIGURE 2

Crack along fillet radius

from upper edge (both 

fitting halves)

Crack starts from bolt

hole and may extend

through gusset

Crack may form

around periphery of

outboard holes
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 20 of 23

SERVICE BULLETIN

SA226 SERIES

FIGURE 3

MAIN SPAR

(LH SHOWN, RH OPPOSITE)

0.190/0.194 Dia Hole

(Pick up pilot holes in 

27-22124 Splice Plate)

NAS6603-4 Bolt

NAS1149F0332P Washer

MS21042-3 Nut

(2 Places)

(See Note 1)

0.190/0.194 Dia Hole

(Pick up pilot holes in 

27-22124 Splice Plate)

NAS6603-5 Bolt

NAS1149F0332P Washer

MS21042-3 Nut

(16 Places)

4.064

(See Note 1)

3.534

(See Note 2)

See Note 4

27-22121 Fitting

27-22123 Fitting

27-22124 Splice Plate

(See Note 3)

27-22124 Splice Strap

(See Note 1)

0.23

0.05

(Min.

clearance)

Note 1: Effective for SA226-T(B) 394 and up, TC 398 and up.

Note 2: Effective for all SA226 serial numbers not covered by Note 1.

Note 3: Fay surface seal in accordance with SA226/227 Structural Repair Manual 51-30-03.

Note 4: Dimensions shown are design parameters. Adjust to match aircraft conditions if

 necessary. Maintain 2D edge distance on all fastener locations.

Note 5: All dimensions are in inches.

Outboard

Up

Aft

Up

0.60

0.35
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 21 of 23

SERVICE BULLETIN

SA226 SERIES

FIGURE 4

AFT SPAR

(LH SHOWN, RH OPPOSITE)

0.91 0.34

27-22137 Splice Plate

(See Note 3)

27-22136 Fitting

2.538

(See Note 1)

2.478

(See Note 2)

27-22135 Fitting

0.190/0.194 Dia Hole

(Pick up pilot holes in 

27-22137 Splice Plate)

MS24694-S54 Screw

NAS1149F0332P Washer

MS21042-3 Nut

(4 Places)

0.190/0.194 Dia Hole

(Pick up pilot holes in 

27-22137 Splice Plate)

NAS6603-5 Bolt

NAS1149F0332P Washer

MS21042-3 Nut

(6 Places)

See Note 4

Note 1: Effective for SA226-T(B) 394 and up, TC 398 and up.

Note 2: Effective for all SA226 serial numbers not covered by Note 1.

Note 3: Fay surface seal in accordance with SA226/227 Structural Repair Manual 51-30-03.

Note 4: Dimensions shown are design parameters. Adjust to match aircraft conditions if

 necessary. Maintain 2D edge distance on all fastener locations.

Note 5: All dimensions are in inches.

Outboard

Up

Aft

Up
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 22 of 23

SERVICE BULLETIN

SA226 SERIES

VIEW LOOKING AFT LH SIDE

See Notes on page 23.

FIGURE 5

3 Fasteners Above

Edge of Cutout

27-22025

DOUBLER

Repair Strap

See Note 4

Install on Top

of 27-22025

Doubler

See Note 2

See Note 1

Spar

Wing-to-Fuselage

Mount Assy

Fuselage Frame

B.L. 0.00
Issued: July 27, 2012

Revised: May 13, 2013

226-53-016 R1

Page 23 of 23

SERVICE BULLETIN

SA226 SERIES

NOTES:

 1. Permissible to trim edge of doubler cutout flush with frame web.

 2. Permissible to trim corner to minimum 0.50 radius.

 3. The Main Spar is shown but similar modifications are allowed to the 27-22025

 Doublerat the Aft Spar location.

 4. For SA226-T/-T(B)/-TC S/N below 258 and SA226-AT S/N below 067;

 manufacture repair strap from 0.063 thick, 2024-T3, AMS-QQ-A-250/5, 12.15

 in. long X 0.76 in. wide and install as shown.

 5. Conversion coat and prime trimmed edges and repair parts per SA226/227

 Structural Repair Manual (SRM) 51-30-02.

 6. Fay surface seal strap to frames as shown per SA226/227 Structural Repair

 Manual (SRM) 51-30-03 using same fastener type and size per SA226/227

 Structural Repair Manual (SRM) 51-40-01.

 7. All dimensions are in inches.
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 1 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

1. Applicable Specifications Technique 001

2. Applicability Fairchild Metro SA226 and SA227 aircraft. Aircraft have been divided by serial number, 

into 3 groups, based upon type of fitting installed on aircraft. 

3. Purpose

The purpose of this technique is to define the requirements for the Contact Ultrasonic Inspection of Wing 

to Fwd Fuselage Mount for the detection of minimum 0.06” Bolt-hole Cracks with the Bolts in-situ. Refer 

to Figure 1 for on-aircraft Fuselage Mount locations. 

4. Personnel Requirements

Inspection, including interpretation and evaluation of results, shall be performed by an experienced Level 2 

or 3 Ultrasonic Technician, qualified and certified to a standard acceptable to the Operator and Local 

Regulatory Authority. This technique assumes that such technicians are skilled in the orientation and 

interpretation of results obtained with the test equipment; it only supplies information on how to apply these 

skills to Fairchild Metro Aircraft. The technician must also have a good working knowledge of aircraft 

structures, a comprehension of failure characteristics of various metals used in aircraft structures and must 

know the limitations of nondestructive testing available as applied to the aircraft. 

Outbd View 

Inbd/Top View 

FIGURE 1 

Location of Forward Fuselage Mount (Right Side Shown, Left Side Typical) 

Qty. (4) bolt-hole 

locations to be inspected 

using this technique 

Group 1 

 SA226-T S/N 201-291 

SA226-T(B) S/N 276-324 

SA226-TC S/N 201-320 

SA226-AT S/N 001-074 

Group 2 

SA226-T(B) S/N 325-391 

SA226-TC S/N 321-396 

Group 3 

SA226-T(B) S/N 394-417 

SA226-TC S/N 398-419 

SA227 All models including 

commuters SA227-CC/DC
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 2 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

5. Equipment

A) Panametrics Epoch 4 Flaw Detector or equivalent with charger & BNC / Microdot Co-axial cable. 

B) Techna NDT Contact Shear Wave 10MHz Transducers as follows (no substitutions allowed): 

i) 45°A: P/N TEK-5566 (0.25” x 0.20” long housing – See Figure 2A) 

ii) 30°A: P/N TEK-5565 (0.20” x 0.16” long housing – See Figure 2B) 

iii) 30°A: P/N TEK-5568 (See Figure 2C) 

C) Couplant: Light Oil. 

D) Reference Standard Part Number NDT001 (See Figure 5) 

E) Inspection Check Fixture, Group 1, 2 or 3 (See Figures 4A to 4F) 

F) Techna AMF-MR-8FX Flexible Extensions as required - 90° microdot offset preferred (See Figure 3). 

G) Inspection Kit Qty. (3) Check Fixture Templates (group 1,2 and 3), Qty. (2) Bolt Locating Plugs, Qty. (1) 

Co axial cable Qty. (1) Reference standard Qty. (3) Transducers and Qty (2) Flexible extensions (kit 

contains all items needed for inspection except flaw detector and couplant oil) 

 

FIGURE 2A 

TD P/N TEK-5566 

FIGURE 2B 

TD P/N TEK-5565

FIGURE 2C 

TD P/N TEK-5568 

 

FIGURE 3 

Techna AMF-MR-8FX Flexible Extensions
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 3 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

6. Identity aircraft by serial number and use appropriate check fixture, group 1,2 or 3

 

7. (Group 1) Part Preparation and Inspection Limitations

Top Surface and Inboard / Outboard Edges of Mount shall be sufficiently exposed to allow transducer 

manipulation, and shall be free of sealant, loose paint and any debris that could impair Ultrasonic 

Inspection. 

*Note: 100% inspection of all Fitting Mounts may not be possible due to relative positioning of insitu bolt holes in relation to center web and outer radii. Use of Inspection Check Fixture Group 1, 

which includes a Check Fixture Template and Qty. (2) Bolt Locating Plugs, is required prior to 

proceeding with inspection set out in this technique. If entire circumference of all holes cannot 

be inspected, this technique shall not be used. 

7.1 Use of Inspection Check Fixture Group 1

A) Insert Bolt Locating Plugs in both fastener heads and position Check Fixture Template over each 

Fitting Mount, flush to Locating Plugs, as shown in Figure 4B. Assure that edge labeled Inboard (IB) 

is positioned accordingly. Template shall be reversed for use on opposite Fitting Mount. 

*Note: Prior to Check Fixture Template use, remove all fasteners that impede intimate contact 

with Locating Plugs and Fitting Mount surfaces including Center Web as shown in Figure 4B. 

B) Entire circumference of both Bolt Locating Plugs shall be within the boundaries scribed on the Check 

Fixture Template (See Figure 4B). Holes associated with any plugs that fall outside the defined 

boundaries cannot be 100% inspected, and this technique shall not be used. 

FIGURE 4B 

Use of Group 1Check Fixture Template + Bolt Locating Plugs 

FIGURE 4A 

Check Fixture Template Group 1 

Inspection Area Inspection Area

Bolt Locating Plugs (seated in Fastener head) 

Check Fixture 

Template 

Orientate This Side 

Inboard 

Scribed Go/No-Go 

Inspection Boundary 

Scribed Go/No-Go 

Inspection Boundary 
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 4 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

8. (Group 2) Part Preparation and Inspection Limitations 

Top Surface and Inboard / Outboard Edges of Mount shall be sufficiently exposed to allow transducer 

manipulation, and shall be free of sealant, loose paint and any debris that could impair Ultrasonic 

Inspection. 

*Note: 100% inspection of all Fitting Mounts may not be possible due to relative positioning of insitu bolt holes in relation to center web and outer radii. Use of Inspection Check Fixture group 2, 

which includes a Check Fixture Template and Qty. (2) Bolt Locating Plugs, is required prior to 

proceeding with inspection set out in this technique. If entire circumference of all holes cannot 

be inspected, this technique shall not be used. 

8.1 Use of Inspection Check Fixture Group 2: 

A) Insert Bolt Locating Plugs in both fastener heads and position Check Fixture Template over each 

Fitting Mount, flush to Locating Plugs, as shown in Figure 4D. Assure that edge labeled Inboard (IB) 

is positioned accordingly. Template shall be reversed for use on opposite Fitting Mount. 

*Note: Prior to Check Fixture Template use, remove all fasteners that impede intimate contact 

with Locating Plugs and Fitting Mount surfaces including Center Web as shown in Figure 4D. 

B) Entire circumference of both Bolt Locating Plugs shall be within the boundaries scribed on the Check 

Fixture Template (See Figure 4D). Holes associated with any plugs that fall outside the defined 

boundaries cannot be 100% inspected, and this technique shall not be used. 

FIGURE 4D 

Use of Group 2 Check Fixture Template + Bolt Locating Plugs 

FIGURE 4C 

Check Fixture Template Group 2 

Inspection Area Inspection Area 

Bolt Locating Plugs (seated in Fastener head) 

Check Fixture 

Template 

Orientate This Side 

Inboard 

Scribed Go/No-Go 

Inspection Boundary 

Scribed Go/No-Go 

Inspection Boundary 

IB
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 5 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

 

9. (Group 3) Part Preparation and Inspection Limitations 

Top Surface and Inboard / Outboard Edges of Mount shall be sufficiently exposed to allow transducer 

manipulation, and shall be free of sealant, loose paint and any debris that could impair Ultrasonic 

Inspection. 

*Note: 100% inspection of all Fitting Mounts may not be possible due to relative positioning of insitu bolt holes in relation to center web and outer radii. Use of Inspection Check Fixture group 3, 

which includes a Check Fixture Templates (2) and Qty. (2) Bolt Locating Plugs, is required prior 

to proceeding with inspection set out in this technique. If entire circumference of all holes cannot 

be inspected, this technique shall not be used. 

9.1 Use of Inspection Check Fixture Group 3 (consists of qty 2 templates the narrow of which is 

used for the outboard side of the fitting): 

 

A) Insert Bolt Locating Plugs in both fastener heads and position Check Fixture Template over each Fitting 

Mount, flush to Locating Plugs, as shown in Figure 4F. Assure that edge labeled Inboard (IB) is positioned 

accordingly. Templates shall be reversed for use on opposite Fitting Mount. 

*Note: Prior to Check Fixture Template use, remove all fasteners that impede intimate contact with 

Locating Plugs and Fitting Mount surfaces including Center Web as shown in Figure 4F. 

B) Entire circumference of both Bolt Locating Plugs shall be within the boundaries scribed on the Check Fixture 

Template (See Figure 4F). Holes associated with any plugs that fall outside the defined boundaries cannot 

be 100% inspected, and this technique shall not be used. 

FIGURE 4E 

Check Fixture Templates Qty (2 pieces) one wide and one narrow 

Inspection Area Inspection Area 

FIGURE 4F 

Use of Group 3 Check Fixture Template + Bolt Locating Plugs 

Bolt Locating Plugs (seated in Fastener head) 

Check Fixture 

Template (Narrow) 

Orientate This Side 

Inboard 

Scribed Go/No-Go 

Inspection Boundary Scribed Go/No-Go 

Inspection Boundary 

Orientate This Side 

Inboard 

Check Fixture 

Template (Wide) 

3A Wide 3B Narrow

IB IB 
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 6 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

10. Reference Standards

A) The Reference Standard is Part Number NDT001 as shown in Figure 5, and is representative of 

parts being inspected in composition, condition, surface finish, approximate dimensions, and 

significant processes. 

B) The Reference Standard is nominal .380” thick, and contains Qty. (2) ~ .315” diameter holes with 

nominal 0.060” EDM corner Notches: (2) common to the upper surface (see Items A & B), and (2) 

common to the lower surface (see Items C & D) as shown in Figure 5. Notches are 0.06” long on 

bolt-hole surface x 0.60” long on the bolt-hole bore. 

Note: Detection of 0.060” Top & Bottom Corner Notches around the entire Hole Circumference was verified 

during technique development using the Transducers specified in this technique. 

A 

FIGURE 5 

Reference Standard NDT001

(curvature not depicted for clarity) 

Qty. (2) .315” ± .030” diam. 

holes with qty. (4) EDM 

notches: .060” long on bolthole surface and bore 

Qty. (4) EDM notches: 

.060” long on bolt-hole 

surface and bore 

.380” 

nominal 

1.775” ± 

0.030” 

2.835” ± 

0.030” 

B D

C

NDT001 
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 7 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

11. Inspection Plan (Refer to Figures 6A and 6B for Typical Scanning Surfaces for each Mount 

Fitting)

A) The Ultrasonic Inspection of the Fuselage Mounts shall be performed in accordance with Section 11 

of this technique. 

B) Ultrasonic Inspection coverage shall be 100% of the entire circumference of qty. (4) holes (top and 

bottom) in both left side Mount and right side Mount pairings (qty. 2 holes each). 

C) The inspection method is Manual Contact Angle Beam, and shall be performed from the Top 

Surface, Inboard and Outboard Edges of each Mount. Refer to Figures 6A and 6B for inspection 

surfaces. 

D) The 30° Angle Beam Transducer P/N TEK-5565 (or alternate TEK-5568 if space permits) shall be 

used for inspection from the Inboard and Outboard Edges for the detection of top and bottom 

surface bolt-hole cracks (See Figures 6A & 6B). 

E) The 30° Angle Beam Transducer P/N TEK-5565 (or alternate TEK-5568 if space permits) shall be 

used from the Top Surface for the detection of top surface bolt-hole cracks (See Figures 6A & 6B). 

F) The 45° Angle Beam Transducer (P/N TEK-5566) shall be used from the Top Surface for the 

detection of bottom surface bolt-hole cracks (See Figures 6A & 6B). 

FIGURE 6B 

Mount – Typical Plan View and Transducer Scanning Placement

Outbd Edge Inbd Edge

FIGURE 6A 

Mount – Typical Side View and Transducer Scanning Placement

(curvature not depicted for clarity) 

Top 

Surface Top 

Surface

Top 

Surface 

Top 

Surface

Outbd Edge Inbd Edge 
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 8 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

12. Instrument Settings 

Panametrics Epoch 4: 

Gain: Cal. Gain & Scan Gain (as required) Wave: Fullwave 

Reject: 0% Energy: Max 

Range: 1.500 in. Damping: 50 Ω

Velocity: 0.1230 in/usec. Mode: Pulse-Echo 

Zero:  0.000 usec. Band: > 8.0 Mhz 

Angle: 0° Pulser: Square 

Thickness: 0.000 in. Echo Trigger: Edge 

*Gate to be adjusted to monitor area of interest. 

*Note: Settings defined above are recommended. Alternate settings may be used provided that 

calibration parameters defined in Section 13 can be achieved. If an equivalent Flaw Detector Instrument 

is used, settings shall be similarly adjusted to optimize defect detection as specified in Section 13. 

13. Calibration 

Calibration shall be performed using Reference Standard NDT001 immediately prior to and after part 

inspection, whenever an indication is detected, and anytime Calibration is suspect. 

Calibration is required for each transducer / inspection set-up to establish baseline amplitude and time 

base reference points, and to provide technician with typical signal presentation of defect coming off bolt 

hole. Depending on differences between Reference Standard and Inspection Specimen, on-aircraft 

adjustment may be required as specified in Section 14. 

A) Surface Scan: Bottom Notch (See Figure 7)

1) Connect the 45° TEK-5566 Angle Beam Transducer. Position at ~1⁄2 Skip from the Bolt-hole as shown in 

Figure 7 (Surface distance from transducer exit point to edge of hole for bottom reflection should be ~ 

.380”, aim towards bolt-hole and maximize response. 

2) Position front surface response on left side of screen and the 1⁄2 Skip Bolt-hole signal at mid screen. 

Adjust gain to set signal from bolt hole to 100% Full Screen Height. 

3) Using the bolt-hole response as a reference, manipulate the Transducer using a rotational and orbital 

motion (See Figure 8) to produce a response from the Bottom Surface EDM Notch (See defects C and D 

in Figure 7). Maximize defect response. You should be able to separate this indication from the Bolt-hole 

response so that it is easily discernible, and signal amplitude from EDM Notch is minimum 50% Full 

Screen Height. Screen presentation of signal separation will appear as shown in Figure 11B. 
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 9 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

A 

B D

C

FIGURE 7 

45° TEK-5566 Calibration 

FIGURE 8 

Transducer Movement
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 10 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

B) Surface Scan: Top Notch (See Figure 9)

1) Connect the 30° TEK-5568 Angle Beam Transducer (or TEK-5565 if position on the on-aircraft Mount 

requires the smaller contact surface). Position at ~1 Skip from the bolt-hole as shown in Figure 9, aim 

towards bolt-hole (Surface distance from transducer exit point to top edge of hole should be ~ .439”), 

and maximize response. 

2) Position front surface response on left side of screen and ~ 1 Skip Bolt-hole response at mid screen. 

Adjust gain to set signal from bolt hole to 100% Full Screen Height. 

3) Using the bolt-hole response as a reference, manipulate the Transducer using a rotational and orbital 

motion (See Figure 8), to produce a response from the Top Surface EDM Notch (See defects A and B in 

Figure 9). Maximize defect response. You should be able to separate this response from the Bolt-hole 

response so that it is easily discernible and signal amplitude from EDM Notch is minimum 50% Full 

Screen Height. Screen presentation should appear as shown in Figure 11B. 

A 

B D

C

FIGURE 9 

30° TEK-5568 (TEK-5565 alternate)
Technique 001 Wing to Fuselage Mount Ultrasonic Inspection Technique

UT Wing to Fuselage Mount Technique Page 11 of 17 22 June 2012

SUPPLEMENT A – SB 226-53-016 

C) Edge Scan: Top & Bottom Notches (Ref. Figure 10)

1) Connect the 30° TEK-5565 Angle Beam Transducer. Position along edge of Reference Standard and 

aim towards Bolt-hole as shown in Figure 10. Maximize response. 

2) Position Front Surface Response on left side of screen & Bolt-hole response at mid screen & adjust to 

100% Full Screen Height. 

3) Manipulate the Transducer to aim slightly towards the Top Surfaces using the Bolt-hole response as a 

reference to produce a response from the Top Surface EDM Notch & maximize. You should be able to 

separate this response from the Bolt-hole response so that it is easily discernible and signal amplitude 

from EDM Notch is minimum 50% Full Screen Height. 

4) Manipulate the Transducer to aim slightly towards the Bottom Surface using the Bolt-hole response as a 

reference to produce a response from the Bottom Surface EDM Notch & maximize. You should be able 

to separate this response from the Bolt-hole response so that it is easily discernible and signal amplitude 

from EDM Notch is minimum 50% Full Screen Height. 

14. Inspection Procedure

*Note: Do not proceed with inspection if bolt-holes cannot be 100% inspected as specified per 

Section 6 of this technique. 

*Note: Figures 11, 12, and 13 provide typical side and plan view part configuration for clarity. 

Inspections shall be performed for opposite hand configurations as specified. 

Complete all inspections as specified in Section 14A through 14D, and per Table 1: Inspection Check Sheet. 

FIGURE 10 

30° TEK-5565 Calibration 

A

B D

C

Transducer placed on edge of reference 

standard should not produce a response from 

the reference hole or Defect B 
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A) Surface Scan: Bottom Surface Bolt-hole Cracks (Refer to Figure 11)

1) Following the same procedure used when scanning the Reference Standard NDT001, position the 45° 

TEK-5566 Angle Beam Transducer at ~1⁄2 Skip from the Bolt-hole, aim towards Bolt-hole & maximize 

response. 

Based on a nominal part thickness of 0.380” the surface distance should be ~ 0.380” from transducer 

exit point to hole-bore & ~ 0.236” from transducer exit point to outer edge of washer. (See Figure 11)

Note that part thickness varies from ~ 0.290” to 0.360”, which will vary surface distances accordingly. 

*Note: use of Techna AMF-MR-8FX Flexible Extensions or equivalent may be required for access. 

2) Position Front Surface Response on left side of screen and 1⁄2 Skip Bolt-hole response at mid screen. 

Adjust gain to set signal from bolt-hole to 100% Full Screen Height. Add 6db Scanning Gain. 

3) Using the bolt-hole response as a reference, scan around the entire circumference of all Bolt-holes 

slowly and carefully using a rotational and orbital motion as shown in Figure 8. Scanning shall be 

performed in both clockwise and counter-clockwise directions. 

FIGURE 11 

45° TEK-5566 
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SUPPLEMENT A – SB 226-53-016 

FIGURE 11A 

Typical Response from Bolt Hole

FIGURE 11B 

Typical Response of Defect Coming off Bolt Hole

Defect

Bolt-hole

Bolt-hole 
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B) Surface Scan: Top Surface Bolt-hole Cracks (Refer to Figure 12)

1) Following the same procedure used when scanning Reference Standard NDT001, position the 30° TEK5568 Angle Beam Transducer (or alternate TEK-5565 if used for calibration and position on the onaircraft Mount requires the smaller contact surface) at ~1 Skip from the Bolt-hole, aim towards Bolt-hole 

and maximize response. 

Based on a nominal part thickness of 0.380” the surface distance should be ~ 0.438” from transducer 

exit point to hole-bore & ~ 0.294” from transducer exit point to outer edge of washer. (See Figure 12)

Note that part thickness varies from ~ 0.290” to 0.360”, which will vary surface distances accordingly. 

*Note: use of Techna AMF-MR-8FX Flexible Extensions or equivalent may be required for access. 

2) Position Front Surface Response on left side of screen and 1 Skip Bolt-hole response at mid screen. 

Adjust gain to set signal from bolt-hole to 100% Full Screen Height. Add 6db Scanning Gain. 

3) Using the bolt-hole response as a reference, scan around the entire circumference of all Bolt-holes 

slowly and carefully using a rotational and orbital motion as shown in Figure 8. Scanning shall be 

performed in both clockwise and counter-clockwise directions. 

FIGURE 12 

30° TEK-5568 or TEK-5565 alternate 
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C) Inbd Edge Scan: Top & Bottom Bolt-hole Cracks (Refer to Figure 13)

1) Following the same procedure used when scanning Reference Standard NDT001, position 30° TEK5568 Angle Beam Transducer (or alternate TEK-5565 if used for calibration, and position on the onaircraft Mount requires the smaller contact surface) along Inbd Edge of Mount, aim towards Bolt-hole 

and maximize response (See Figure 13). 

*Note: use of Techna AMF-MR-8FX Flexible Extensions or equivalent may be required for access. 

2) Position Front Surface Response on left side of screen and Bolt-hole response at mid screen. Adjust 

gain to set signal from bolt-hole to 100% Full Screen Height. Add 6db Scanning Gain. 

3) Start scanning at the outer most corner or Mount Edge. No bolt-hole response should be displayed in 

this position. Using the bolt-hole response as a reference, scan along the entire length of the Inbd Edge 

slowly and carefully with the Transducer aimed slightly towards the Top Surface. Scanning shall 

performed with the transducer directed both Forward and Aft as shown in Figure 13. 

4) Repeat Item C) 3 above but with the Transducer aimed slightly towards the Bottom Surface Scanning 

shall be performed with the transducer directed both Forward and Aft as shown in Figure 13. 

D) Outbd Edge Scan: Top and Bottom Bolt-hole Cracks (Refer to Figure 13) 

1) Repeat Section 14C Items 1 to 4 for inspection from Outbd Edge. 

FIGURE 13 – Edge Scan 

30° TEK-5566 

Outbd Edge Inbd Edge

Outbd Edge Inbd Edge 
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15. Acceptance Criteria

A) All crack indications are Unacceptable. 

16. Discontinuity Evaluation

A) All responses similar to the applicable Reference Notch on Reference Standard NDT001 (i.e. defect 

signal able to be separated from the Bolt-hole response) shall be regarded as a Crack indication 

regardless of amplitude. 

B) Crack indications shall be verified by performing Eddy Current Bolt-hole inspection after Fastener 

removal. 

17. Part Disposition

A) Parts meeting Section 15 Criteria shall be dispositioned as Acceptable. 

B) Parts not meeting Section 15 Criteria shall be dispositioned as Non-Conforming. 
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TABLE 1

INSPECTION CHECK SHEET

Part ID:

Probe Location Clockwise Counter-Clockwise 

Top Surface 

30° (TEK-5565 or TEK-5568) 

45° (TEK-5566) 

Probe Direction: Aft Probe Direction: Fwd 

Inbd Edge 

30° (TEK-5565 or TEK-5568) 

Probe Direction: Aft Probe Direction: Fwd 

Outbd Edge 

30° (TEK-5565 or TEK55-68)