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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: 234-62-0008

Date: 12/06/2013

Revision: 1

ATA System: Rotors

SUBJECT: Inspection of the Rotor Blade Trailing Edge

Revision 1 corrects typographical errors in several compliance references.

1. Planning Information

A. Effectivity:

B. Concurrent Requirements 

N/A

C. Previous Modifications

N/A

D. Reason

To detect dis-bonding conditions in the trailing edge of the rotor blades.

E. Description

This service bulletin provides instructions for a visual and a detailed special coin tap inspection 

of the trailing edge of the rotor blades.

F. Compliance

Compliance with this service bulletin must be accomplished within 50 flight hours after receipt 

of this service bulletin.

(1) Perform an initial inspection of the rotor blades as follows.

(a) Visual inspections per Para 3.A.

(b) A coin tap test per Para 3.B.

(2) Recurring inspections to be performed every 500 flight hours after the initial inspection.

(a) Perform general and close visual inspections per Para 3.A.

(1) Aircraft Affected S/N

CHI Model 234 ALL

(2) Spares Affected S/N

Rotor Blades Part Number 

114R1702 All Dash Numbers

ALL 
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-62-0008

(b) If indications of dis-bonding are noted during the visual inspections perform a coin 

tap inspection per Para 3.B.

(3) Perform a recurring coin tap inspection every 3000 flight hours after initial inspection per 

Para 3.B.

(4) Perform visual and coin tap inspections on spare rotor blades per Para 3.A. and 

Para 3.B. prior to installation.

G. Approval

This service bulletin is FAA approved.

H. Manpower

Approximately 1 hour and a crew of 1 is required to accomplish the visual inspection. Approximately 4 hours and a crew of 1 is required to accomplish the coin tap inspection.

I. Tooling

N/A

J. Weight and Balance

N/A

K. Electrical Load Data

N/A

L. Software Accomplishment Summary

N/A

M. References

234-2 Maintenance Manual

N. Publications Affected

N/A

O. Material Requirements

N/A

P. List of Components 

N/A

2. Definitions

A. General Visual Inspection (GVI)

A visual examination of an interior or exterior area, installation, or assembly to detect obvious 

damage, failure, or irregularity. This level of inspection is made from within touching distance 

unless otherwise specified. A mirror may be necessary to enhance visual access to all 

exposed surfaces in the inspection area. This level of inspection is made under normally available lighting conditions such as daylight, hangar lighting, flashlight, or drop light, and may 

require removal or access panels or doors. Stands, ladders, or platforms may be required to 

gain proximity to the area being checked.

B. Close Visual Inspection

This type of inspection is detailed in nature and accomplished using ample lighting, at no more 

than arm’s length, and using 10X magnification, as appropriate. 

C. Detailed Special Inspection – Coin Tap Method

The “Coin Tap” method is a common technique/procedure used for detecting voids or delaminations in thin face sheet honeycomb construction. When tapping any area, a clear, sharp 

ringing sound is indicative of a well-bonded solid structure, while a dull sound or thud indicates 

a void or delamination. 
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-62-0008

3. Accomplishment Instructions

A. Visual Inspections

(1) General Visual Inspection

(a) Clean the rotor blades. Refer to 234-2 Maintenance Manual, Section 12-22-00, 

Para. 4.F., on page 204.

(b) Perform a general visual inspection of the entire rotor blade, looking for obvious 

defects, damage and dis-bonds by looking down the entire length of the rotor 

blade and paying particular attention to ripples, which may indicate a dis-bond 

condition.

(2) Close Visual Inspection

(a) Perform a close visual inspection at no more than arm’s length. Use ample 

lighting and 10X magnification, as necessary.

(b) Angle the lighting and plane of view as necessary, such that irregularities in the 

surface are visible. Irregularities may indicate a dis-bond condition.

(3) Report information to Columbia Helicopters Engineering as soon as practical, but no 

later than 90 days from the date of the inspection.

(4) If dis-bonding is greater than the limits provided in 234-2 Maintenance Manual, Section 

62-11-00, contact Columbia Helicopters Engineering for repair assistance. Repair or 

replace the blade prior to further flight. 

B. Detailed Special Inspection – Coin Tap Method

(1) Rotor blade trailing edge dis-bonding can be identified by tapping the surface with a 

solid metal disk. The disk or coin should be approximately 1.5" diameter and 

approximately 0.10" thick. Bonded areas will produce a sharp ringing sound, dis-bonded 

areas will produce a dull hollow sound.

(2) Perform the coin tap inspection as follows:

(a) Clean the area to be inspected and check the surface visually.

(b) To ensure full coverage of the inspection area, the tapping pattern must be 

performed in both the spanwise and chordwise directions as follows:

1: Tap the surface approximately every 1 to 2 square inches over the entire 

area depicted by the gray area in Figure 1. 

2: Repeat step 1: on the underside of the blade.

Trailing Edge Inspection Area

Figure 1

(c) Hold the disk between the thumb and second finger slightly above the center. 

Using the edge of the disk, tap lightly, but firmly, with a rhythmic speed along the 

trailing edge as described in step (b) while lightly touching the adjacent surface 

with the finger tips.
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 COLUMBIA HELICOPTERS INC. SERVICE BULLETIN NUMBER 234-62-0008

THIS INSPECTION REQUIRES THE OPERATOR TO DISTINGUISH 

CHANGES IN SOUND AND VIBRATION.

(d) Void areas will produce a change in sound and a slight vibration of the trailing 

edge. A void can be identified by a dull hollow sound accompanied by feeling the 

vibration in the trailing edge adjacent to the void.

(e) Identify any area that produces a change of sound or vibration.

1: Examine the surrounding area to determine the size of the dis-bonded area.

2: Outline the edge of the void, using a suitable marker.

(f) If dis-bonding of the fairing skin and core (Figure 2) is detected, refer to 234-2 

Maintenance Manual, Section 62-11-00 for serviceability and repair before further 

flight in accordance with 234-2 Maintenance Manual, Section

62-11-30.

1: Report information to Columbia Helicopters Engineering as soon as 

practical, but no later than 90 days from the date of the inspection.

2: If dis-bonding is greater than the limits provided in 234-2 Maintenance 

Manual, Section 62-11-00 Inspection/Check, contact Columbia Helicopters 

Engineering for repair assistance. Repair or replace the blade prior to 

further flight.

(g) If dis-bonding of the trailing edge is detected, refer to 234-2 Maintenance Manual, 

Section 62-11-00 for serviceability and repair before further flight, in accordance 

with 234-2 Maintenance Manual, Section 62-11-40.

1: Report information to Columbia Helicopters Engineering as soon as 

practical, but no later than 90 days from the date of the inspection.

2: If dis-bonding is greater than the limits provided in 234-2 Maintenance 

Manual, Section 62-11-00 Inspection/Check, contact Columbia Helicopters 

Engineering for repair assistance. Repair or replace the blade prior to 

further flight. 

Rotor Blade Trailing Edge Cross-Section

Figure 2

4. Log Book Entry

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

book or component records.

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

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