Commonwealth legislation

AD/ELECT/4 - Magnetos BTH - Earthing Modification

RepealedCTH

This Act has been repealed and is no longer in force. It is retained for historical reference.

Jurisdiction

Commonwealth

Collection

legislative instrument

Plain English Summary

3/10 complexity

This Airworthiness Directive requires a mandatory modification to BTH magnetos (models AG4, SG4, MC1 with screened contact breaker covers) before installation. Maintenance engineers and owners must ensure the contact-breaker cover’s earthing connection is corrected — removing and refitting the earthing spring/brush and making small drill/cut alterations to a brass insert — to secure proper grounding.

It prevents magneto switch failure that could stop the engine from shutting down when ignition is turned off.

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AD/ELECT/4 - Magnetos BTH - Earthing Modification

COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY

SCHEDULE OF AIRWORTHINESS DIRECTIVES

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Electrical Equipment

AD/ELECT/4 Magnetos BTH - Earthing Modification NK

Applicability: BTH AG4, SG4 and MC1 types with screened contact breaker covers.

Requirement: Modify the contact breaker cover as follows to ensure positive connection of the magneto switch lead to the magneto earthing spring and brush assembly.

Remove the earthing spring and brush assembly from the contact breaker cover.

2. Remove switch lead set screw and tab washer. Drill out thread for this screw in insert.

3. Cut channel of approximately 1/8" width in brass insert, sloping from bottom of drilled hole to top of insert for earthing spring as shown in Fig. 1 of this Section. Radius all corners to remove sharp edges.

Note: This channel may be conveniently cut by using a small grinding wheel (3/32 in. or 1/8 in. diameter) in an air or electric drill.

4. Replace contact breaker cover spring and brush assembly.

Magnetos BTH - Earthing Modification

or ANO 107.2.16.2.3.

Compliance: Before installation in an aircraft.

Source text

Sourced from the Federal Register of Legislation (legislation.gov.au), CC BY 4.0.

1 AD/ELECT/4 - Magnetos BTH - Earthing Modification