1959 deHavilland Way.

Sidney, B.C.

Canada V8L 5V5

Tel: (250) 656 - 7227

DHC-2 

Beaver 

29-April-2013 A.S.B. V2/0007

Revision ‘NC’ Page 1 of 6

ALERT SERVICE BULLETIN

ATA SYSTEM: 5510 NUMBER: V2/0007

I. PLANNING INFORMATION

A. Effectivity

Aircraft Affected: All DHC-2 aircraft.

NOTE: The instructions in this Service Bulletin are only applicable to the systems and parts 

installed at the time of delivery on the aircraft or as changed by Viking Service 

Bulletin(s). Before you do this bulletin, examine all STC or equivalent action changes to 

make sure this bulletin can be completed.

B. Reason

A DHC-2 horizontal stabilizer attach bracket has been found with two (2) MS21042 

locknuts broken. Upon further investigation, Viking has found a quality issue with the 

locknuts. (See Figure 3).

C. Description

Some MS21042 Locknuts have been identified as being affected by a manufacturing 

issue, making them susceptible to premature failure due to cracking. This issue had 

previously been identified amongst other aircraft manufacturers and corrective action 

publications had been distributed. The fact that Viking has recently been supplied with a 

quantity of sub-quality locknuts, indicates that sub-quality parts continue to be available. 

Due to the recent DHC-2 horizontal stabilizer bracket attach locknut issue, the following 

inspection / replacement shall be completed for all DHC-2 aircraft.

SUBJECT: INSPECTION AND/OR REPLACEMENT OF MS21042 LOCKNUT

IN HORIZONTAL STABILIZER (P/N C2TP1A)
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D. Compliance

All DHC-2 operators shall inspect their aircraft within 48 hours of receiving this Service 

Bulletin. If MS21042 locknuts are found, they must be replaced by MS21044 locknuts

before further flight.

E. Approval

The technical content of this Service Bulletin has been approved under the authority of 

Transport Canada Civil Aviation (TCCA) Design Approval Organization (DAO) 04-V-02.

F. Manpower

Approximately 1 hour labour will be required to perform the inspection of the locknuts. 

Approximately 12 hours is required if locknuts must be replaced with new ones.

NOTE: Visual inspection labour may be considerably more if stabilizer assembly must 

be removed to properly inspect locknuts.

G. Weight and Balance

Not affected.

H. Electrical Load Data

Not affected.

I. Publications Affected

None.

J. References

This Service Bulletin is self-contained. No additional drawing or documents are required 

to implement the Accomplishment Instructions.

Note: For more information please contact:

Viking Air Limited FAX: 250-656-0673

Technical Support Telephone Numbers:

1959 de Havilland Way Regional: 250-656-7227

Sidney, British Columbia North America: 1-866-49-ATLAS

Canada, V8L 5V5 International: 1-800-6727-6727

technical.support@vikingair.com
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II. ACCOMPLISHMENT INSTRUCTIONS

A. Preparing for Inspection

1. Remove tailcone section as per PSM 1-2-2 Sec. 2.16;

2. If visual inspection is impeded in any way, remove stabilizer assembly as per PSM 1-

2-2, Sec. 2.18.1.

B. Inspection Procedures

1. Using a flashlight, visually inspect quantity six (6) locknuts (as indicated in Figure 1) 

for type installed:

a) If the installed locknuts are NOT MS21042 (ref. Figure 2A, 2B, 2C for visual 

aid of possible locknuts installed in this application) skip to Step II. D;

b) If the installed locknuts are MS21042 (ref. Figure 2D for visual aid), continue 

to Step II. C.

C. Replacement of Affected Locknuts

1. Remove stabilizer assembly as per PSM 1-2-2, Sec. 2.18.1;

2. Remove affected locknuts;

NOTE: if locknut is completely missing, inspect area for pieces of broken locknut to 

eliminate Foreign Object Damage (FOD) potential.

3. Install new MS21044 locknuts (IAW para III. A. table) as per standard practices;

NOTE: Ensure a minimum of two (2) threads on the attach bolts are visible when 

the locknut is installed.

D. Close-Out

1. Re-install stabilizer assembly per PSM 1-2-2, Sec. 2.18.3;

2. Re-install tailcone as per PSM 1-2-2, Sec. 2.16.2.

3. Inform Viking Technical Support of any cracked locknut findings (See I.J. 

References)

E. Recording

After completion of activities make the following entry in the aircraft log book: “Service 

Bulletin No. V2/0007 – INSPECTION OR INSPECTION/REPLACEMENT OF MS21042 

LOCKNUT IN HORIZONTAL STABILIZER (P/N C2TP1A) has been incorporated”.
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III. MATERIAL INFORMATION AND TOOLING

A. Material Information (Parts Required Per Aircraft)

Old Part No. Replacement

Part No.

MS21042-3 MS21044N3

MS21042-4 MS21044N4

B. Material Information

None

C. Tooling – Price and Availability

 Standard aviation hand tools

 Flashlight

 Mirror
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IV. DRAWINGS AND TABLES

FIGURE 1 – MS21042 LOCKNUT LOCATION

LOCKNUT LOCATION
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FIGURE 2A – AN364 LOCKNUT FIGURE 2B – AN 365 LOCKNUT FIGURE 2C – MS21044 LOCKNUT

FIGURE 2D – MS21042 LOCKNUT (ALERT SERVICE BULLETIN SUBJECT)

FIGURE 3 – DISCREPANT MS21042 LOCKNUT