Commonwealth legislation

AD/B767/74 - Hydraulic Power - Ram Air Turbine Wiring

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legislative instrument

Plain English Summary

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What it does: Requires operators of certain Boeing 767 aeroplanes to replace the Ram Air Turbine (RAT) airspeed switch, cap and stow the wire to the air/ground relay, and perform a functional RAT deployment test in accordance with Boeing Service Bulletin 767‑29‑0021 Rev 4.

Who it affects and why it matters: Applies to the models listed in that Service Bulletin and must be done by 30 June 1995 or within 4,000 flight hours after 31 March 1994. The stated aim is to prevent RAT non‑deployment from switch failure, which could cause loss of hydraulic power.

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AD/B767/74 - Hydraulic Power - Ram Air Turbine Wiring

COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY

SCHEDULE OF AIRWORTHINESS DIRECTIVES

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Boeing 767 Series Aeroplanes

AD/B767/74 Hydraulic Power - Ram Air Turbine Wiring 4/94

Applicability: Model 767 series aeroplanes listed in Boeing Service Bulletin 767-29-0021 Revision 4 dated 12 May 1988.

Requirement: Unless previously accomplished; replace the Ram Air Turbine (RAT) airspeed switch; cap and stow the wire between the RAT airspeed switch and the air/ground relay and then perform a functional test of the RAT deployment system; in accordance with Boeing Service Bulletin 767-29-0021 Revision 4 dated 12 May 1988.

Note: FAA AD 94-01-02 Amdt 39-8784 refers.

Compliance: Prior to 30 June 1995 or within 4000 hours time in service after 31 March 1994, whichever occurs later.

Background: The aircraft manufacturer has received reports of the RAT airspeed switch relay chattering during take-off and landing. Although the relay is designed and tested to cycle in excess of one million times, it was only expected to cycle once each flight, therefore the switch may fail due to excessive cycling.

If the failed switch remained in the open position the RAT may not automatically deploy, leading to a possible loss of hydraulic power. Compliance with this Directive is intended to prevent the inability to maintain hydraulic system power in the event that power is lost in both engines.

Source text

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

1 AD/B767/74 - Hydraulic Power - Ram Air Turbine Wiring