Commonwealth legislation

AD/VIPER/4 - Blow-Off Valve

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This Act has been repealed and is no longer in force. It is retained for historical reference.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

2/10 complexity

What this does: This rule requires regular inspections of the blow-off valve on specific Rolls Royce Viper jet engines.

Who it affects: Anyone operating or maintaining aircraft with Viper Mk. 521 or 522 engines.

What you must do: Follow the instructions in Rolls Royce Service Bulletin No. 75-31 (or an alternative Civil Aviation Order) to inspect the blow-off valve. This isn't a one-off fix—you need to keep checking it repeatedly.

Why it matters: If these valves get stuck (a problem called "stiction"), it can cause the engine to surge or stall mid-flight. This directive was reissued specifically to make sure operators keep checking this part, not just fix it once.

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AD/VIPER/4 - Blow-Off Valve

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COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY

SCHEDULE OF AIRWORTHINESS DIRECTIVES

View image in the official source Rolls Royce Turbine Engines - Viper Series

AD/VIPER/4 Blow-Off Valve 3/90

Applicability: Viper Mk. 521, 522 engines.

Requirement: 1. Action in accordance with Rolls Royce Service Bulletin No. 75-31, or

CAO 106 AD/RRT-V/14. Compliance: Effective 22 March 1990.

Background: This Directive has been reissued to require repetitive inspection of the blow-off valve.

Engine surge/stall events have been attributed, in part, to stiction of the blow-off valve.

Source text

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