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Model 234

 SERVICE BULLETIN 

This document and any technical data contained is proprietary to Columbia Helicopters Incorporated (CHI) 

and shall not be used, released, or disclosed, in whole or in part without written permission from CHI.

Number: 234-54-0004

Date: 11/22/2013

Revision: 0

ATA System: Nacelles/Pylons

SUBJECT: Aft Pylon STA 534 and 594 Inspection

1. Planning Information

A. Effectivity:

B. Concurrent Requirements 

None

C. Previous Modifications

None

D. Reason

To inspect the aft pylon structure in the areas of the STA 534 and 594 tension attachment fittings.

E. Description

This service bulletin provides instructions for recurring detailed special inspection of the aft 

pylon STA 534 and 594 structure surrounding the tension attachment fittings above WL +72, 

using the dye penetrant method of inspection.

F. Compliance

Compliance with this service bulletin is mandatory and must be accomplished within 50 flight 

hours after receipt of this service bulletin; and recurring inspections performed every 100 flight 

hours thereafter.

G. Approval

This service bulletin is FAA approved.

H. Manpower

Approximately 6 man-hours are required to accomplish this service bulletin.

I. Tooling

N/A

(1) Aircraft Affected S/N

CHI Model 234 ALL
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-54-0004

J. Weight and Balance

This service bulletin has no effect on weight and balance.

K. Electrical Load Data

N/A

L. Software Accomplishment Summary

N/A

M. References

234-2 Maintenance Manual

234-3 Structural Repair Manual

N. Publications Affected

234-2 Maintenance Manual

O. Materials and Equipment Requirements

2. Detailed Special Inspection – Dye Penetrant Method

WEAR APPROPRIATE PERSONAL PROTECTIVE DEVICES AND USE ADEQUATE 

VENTILATION DURING THE CLEANING AND PAINT REMOVAL PROCESSES.

A. Requirements

(1) Personnel performing this inspection must hold a current A&P certificate, or equivalent, 

and be familiar with the liquid penetrant inspection method.

(2) Temperature limits for structure undergoing inspection: 45° to 125°F (7.2° to 51.7°C).

(3) The inspection areas of interest are the areas surrounding the STA 534 and 594 forward and 

aft tension attachments. Refer to Figure 1 for a general overview of the inspection areas.

(4) Due to physical limitations, a detailed close visual inspection of the outboard side of the 

aft STA 594 fittings shall be performed. Refer to the shaded area noted in Figure 3.

(a) This type of inspection is detailed in nature and accomplished using ample 

lighting, at no more than arm’s length, and using 3X or better magnification, as 

appropriate. A borescope may be used to perform this inspection.

B. Aircraft Preparation

(1) Prepare the aircraft for safe ground maintenance.

(2) Gain access to the aft pylon upper WL +72 deck, forward and aft of STA 534 and 594.

Nomenclature Part Number Quantity

Acetone ASTM D329 A/R

Borescope Commercially available 1

Cleaning solvent MIL-PRF-680 A/R

Grease remover Ditz-O® DX440 (ALT for MIL-PRF-680) A/R

Naphtha TT-N-97 or TT-N-95 (ALT for MIL-PRF-680) A/R

Cloth, lint-free — A/R

Dye penetrant materials ASTM E 1220, using the Type II, Method C, 

and Nonaqueous developer

1

Paint remover Eldorado PR-3500; MIL-R-8129, or equiv. A/R

Wash primer MIL-C-8514 A/R

Sealant PR1422 B-1/2; AMS-S-8802, Class B A/R
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-54-0004

(3) Clean each set of LH and RH tension attachments and the area surrounding each 

attachment, using cleaning solvent. Refer to Figure 2 and Figure 3.

(4) First Inspection Only – Remove the paint and primer from the areas of interest, as 

depicted in Figure 2 and Figure 3, where practicable. Plus remove an additional one 

inch width of paint and primer extending beyond the areas of interest, where practicable.

It is not necessary to remove the paint and primer from the fittings.

Inspection of the area outboard of each attachment is limited to the exposed 

area between the attachment and the outboard longitudinal structure. 

(a) Apply paint remover using the brush-on method.

(b) Allow at least 15 minutes of contact time to loosen the paint.

(c) Agitate the loosened paint to dislodge it.

(d) Squeegee the stripper and loose paint off the surface, using a non-metallic 

scraper. Collect the loose paint and stripper residue in plastic sheeting.

(e) Flush the area thoroughly using fresh water.

REMOVE THE PAINT AND PRIMER PRIOR TO REMOVING THE FILLET 

SEAL TO PREVENT PAINT REMOVER FROM PENETRATING THE GAPS 

BETWEEN THE STATION FRAME AND THE TENSION FITTINGS.

(5) First Inspection Only – Remove the fillet sealant from around each tension fitting. Use a 

non-metallic scraper, clean cloths, and cleaning solvent or acetone.

Remove the sealant only if it extends more than 1/4" out from the face of the 

fitting or it is damaged during paint and primer removal. 

(6) Subsequent Inspections:

(a) Remove the wash primer from the areas of interest using acetone. Refer to 

Figure 2 and Figure 3.

(b) Remove the fillet sealant if it extends more than 1/4" out from the face of the fitting.
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-54-0004

General Overview of the Inspection Areas

Figure 1
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-54-0004

STA 534 Areas of Interest

Figure 2
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-54-0004

STA 594 Areas of Interest

Figure 3
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-54-0004

C. Inspection Preparation

(1) Clean the area of interest and one inch surrounding that area, using the penetrant 

cleaner/remover and clean cloths to wipe the area clean. Refer to Figure 2 and Figure 3.

(2) Allow adequate time for the cleaner/remover to dissolve any contaminates or organic soils.

(3) Allow a minimum of 30 seconds and up to 5 minutes for the cleaner/remover to completely 

evaporate from the area.

Wait until the area is visibly dry and then double that amount of time to allow 

any residual cleaner/remover to dry completely from any defects.

D. Penetrant Application

(1) Spray a small amount of penetrant into a small, suitable container.

(2) Apply the penetrant to the area of interest, using a cotton swab or small brush. Refer to 

Figure 2 and Figure 3.

(3) Remove any penetrant that drips or goes into other areas, using cleaner/remover and a 

clean cloth.

Care should be taken to keep excess penetrant to a minimum.

(4) Let the penetrant sit (dwell) on the part for 30 minutes minimum to two hours maximum.

(a) Reapply penetrant as necessary to prevent drying during the dwell time.

(b) Clean the penetrant and restart the process, beginning at Para 2.C.(1), if the 

penetrant is allowed to dry.

E. Penetrant Removal

DO NOT SPRAY CLEANER/REMOVER ON THE AREA UNDERGOING INSPECTION. EXCESSIVE USE OF CLEANER/REMOVER COULD RESULT IN AN 

UNDETECTED DEFECT DUE TO FLUSHING PENETRANT OUT OF THE 

DEFECT.

(1) Wipe the penetrant from the surface in one direction only, using a clean cloth or cotton 

swab moistened with cleaner/remover for each wipe.

(2) Use as few wipes as possible.

(3) Stop the cleaning process when the surface is visibly clean.

(4) Allow a minimum of 30 seconds and up to 5 minutes for the cleaner/remover to 

completely evaporate from the area.

Wait until the area is visibly dry and then double that amount of time to allow 

any residual cleaner/remover to dry completely from any defects.

F. Nonaqueous Wet Developer Application

(1) Shake the developer can for at least 30 seconds.

The developer needs to be shaken before each use to allow for proper mixing 

of the developer and volatile carrier.

(2) Spray a light even coat that covers the area of interest and one inch surrounding that area.

(3) Apply two or three light applications of developer, as opposed to one heavy coat.

(4) Wait 15 minutes to allow all indications to fully develop prior to inspecting the area of 

interest.
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-54-0004

G. Inspection

(1) Inspect the area of interest.

(a) A crack may appear as a solid straight or jagged line as shown in Figure 4.

(b) A very tight crack may appear as a series of dots or an interrupted line as shown 

in Figure 5.

(2) Any crack indication within the area of interest is cause for rejection. 

(a) Contact CHI Engineering prior to any further action, if a crack indication is 

detected.

(b) Photograph any questionable indication and forward the photograph to CHI 

Engineering for disposition, prior to any further action.

Example of a Solid or Jagged Line Crack

Figure 4

Example of a Very Tight Crack

Figure 5

H. Post-Inspection Cleaning

RESIDUAL DEVELOPER ATTRACTS MOISTURE, WHICH CAN LEAD TO CORROSION. MAKE SURE ALL RESIDUAL DEVELOPER IS REMOVED FROM THE 

STRUCTURE.

(1) Wipe the area with a cloth saturated with water or cleaning solvent to remove residual 

developer from the surface. Pay particular attention to gaps and crevices.

(2) Repeat wiping until all residual developer is removed from the surface.
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-54-0004

I. Inspection Completion

Perform this procedure if inspection results are negative or after completing necessary repairs, 

as applicable.

(1) Apply one coat of wash primer to the areas where the finish was removed in Para 2.B.(4), 

as directed in 234-3 Structural Repair Manual, Section 51-30-03.

(2) Apply a fillet seal around each tension attachment where it joins the surrounding structure, 

as directed in the 234-3 Structural Repair Manual, Section 51-45-00. Refer to Figure 6.

Sealant application is only required if the sealant was removed for the first 

inspection or if subsequent inspections or repairs require re-application of 

sealant to give proper moisture protection.

Apply the minimum amount of sealant necessary to prevent moisture penetration between the station frame and the tension attachment. Minimal application of sealant allows subsequent inspection without removing the sealant.

(3) Close up the aft pylon.

(4) Restore the aircraft to an airworthy condition.

Typical Fillet Sealant Application

Figure 6

3. Log Book Entry

Upon completion of the work directed in this Service Bulletin, record compliance in the aircraft log 

book.

Should you require any further information or have any questions, please contact: Columbia Helicopters, 

Inc. Engineering, at: contactengineering@colheli.com.