COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
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.
Overview
The Civil Aviation Regulations 1998, as amended, address various safety concerns in aviation through the implementation of Airworthiness Directives. One such directive, AD/B767/74, targets Boeing 767 series aeroplanes and was enacted to address the issue of the Ram Air Turbine (RAT) airspeed switch relay chattering during critical phases of flight, such as take-off and landing. This problem was identified after reports indicated that the switch could fail due to excessive cycling, potentially leading to the RAT not deploying automatically and resulting in a loss of hydraulic power. The directive mandates the replacement of the RAT airspeed switch, capping and stowing the associated wiring, and conducting a functional test in accordance with specified procedures. The objective of this directive is to ensure continued airworthiness and safety by preventing the failure of the RAT system, which could critically affect the aircraft's ability to maintain hydraulic power during flight.
Scope and Application
The Civil Aviation Regulations 1998, specifically Part 39 - 105, addresses the maintenance and operation of aircraft through the Civil Aviation Safety Authority's Schedule of Airworthiness Directives. This legislation applies to Boeing 767 series aeroplanes as listed in Boeing Service Bulletin 767-29-0021 Revision 4 dated 12 May 1988. The regulation mandates that operators of these aircraft must replace the Ram Air Turbine (RAT) airspeed switch, cap and stow the relevant wiring, and perform a functional test of the RAT deployment system. Compliance is required either before 30 June 1995 or within 4000 hours of time in service after 31 March 1994, whichever occurs later. This directive aims to mitigate the risk of the RAT airspeed switch relay chattering during critical phases of flight, which could result in the failure of the RAT to deploy and a consequent loss of hydraulic power.
Key Provisions
The Civil Aviation Regulations 1998, specifically Part 39 - 105, contain an Airworthiness Directive (AD) concerning Boeing 767 series aeroplanes, identified as AD/B767/74 (1). This directive addresses issues with the hydraulic power system, particularly the Ram Air Turbine (RAT) wiring and its airspeed switch. The requirement outlined in the directive mandates that operators of Boeing 767 series aeroplanes listed in Boeing Service Bulletin 767-29-0021 Revision 4 dated 12 May 1988, must replace the RAT airspeed switch if it has not already been replaced. Additionally, operators are required to cap and stow the wire between the RAT airspeed switch and the air/ground relay, followed by a functional test of the RAT deployment system, in accordance with the specified service bulletin (2). Compliance with this directive must be achieved either before 30 June 1995 or within 4000 hours of time in service after 31 March 1994, whichever is later (3).
Operators of Boeing 767 series aeroplanes governed by this AD are required to ensure that the specified modifications and tests are carried out on the RAT system. This includes replacing the RAT airspeed switch to prevent its potential failure due to excessive cycling, which can result in the RAT not deploying automatically and, consequently, the loss of hydraulic power. Operators must adhere to the detailed procedures outlined in Boeing Service Bulletin 767-29-0021 Revision 4, ensuring that all steps are completed correctly to maintain airworthiness (4). Failure to comply with these requirements can result in serious safety implications, including potential loss of hydraulic power during critical phases of flight, such as take-off and landing.
Under the Civil Aviation Regulations 1998, failure to comply with the provisions of this AD can lead to significant consequences. The legislation does not explicitly state the penalties for non-compliance; however, non-compliance with airworthiness directives is generally considered a serious violation. Such violations can result in enforcement actions by the Civil Aviation Safety Authority (CASA), including the issuance of compliance orders, fines, and potential grounding of the aircraft until the required modifications are completed (5). In extreme cases, non-compliance can lead to criminal charges against individuals responsible for the oversight of the aircraft, carrying severe penalties. Therefore, operators must prioritise compliance to avoid these serious repercussions.