COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
DHC-6 (Twin Otter) Series Aeroplanes
AD/DHC-6/57 Voltage Regulators - Inspection and
Provision of Ground Wires
6/85
Applicability: All model DHC-6 Aircraft with S/Nos 531 through 814 (Post Modification No.
6/1590).
Requirement: Inspect the Generator Field Control Relay Panel for the existence of wires between Terminal Block TB-1A, Terminals A4 and C4 and Ground at intercostal C6FS1442-
36. If wires coded 1P80B20N and 2P80B20N exist between terminals A4 and C4 repectively and ground then no further action is required. If no wires exist at these locations, install wires in accordance with the requirements of DeHavilland of Canada
S.B No 6/473. Compliance: Prior to 31 July 1985.
Background: It is believed that during factory incorporation of Mod 6/1590 the two ground wires may have been omitted. The two wires provide “latching” for relays associated with generator overvoltage protection. Failure of these relays to “latch in” after a generator overvoltage may cause the generators to enter a cyclic mode with rising and falling voltages being applied to the aircraft electrical system.
Overview
The Civil Aviation Regulations 1998, administered by the Civil Aviation Safety Authority (CASA), address the need for ensuring the airworthiness of aircraft through various safety directives. One such directive, AD/DHC-6/57, specifically targets DHC-6 (Twin Otter) series aeroplanes with serial numbers between 531 and 814 post-modification number 6/1590. This directive was introduced to rectify a potential safety issue where the installation of two critical ground wires, essential for generator overvoltage protection, might have been omitted during factory modifications. The directive mandates an inspection of the Generator Field Control Relay Panel to ensure the presence of these wires and requires their installation if missing, to prevent potential cyclic generator operation and voltage fluctuations that could compromise the aircraft's electrical system.
The policy objective behind AD/DHC-6/57 is to enhance the safety and reliability of DHC-6 aircraft by addressing a specific modification oversight that could lead to hazardous conditions in flight. By setting a compliance deadline of 31 July 1985, the regulation ensures timely corrective action to mitigate any risk associated with the identified wiring issue.
Scope and Application
The Civil Aviation Regulations 1998, specifically under Part 39 - 105, mandate the application of Airworthiness Directives for certain aircraft models, including the DHC-6 (Twin Otter) Series Aeroplanes. The regulation AD/DHC-6/57 pertains to aircraft with serial numbers ranging from 531 through 814, specifically those that have undergone Post Modification No. 6/1590. This directive requires a thorough inspection of the Generator Field Control Relay Panel to ensure the presence of designated wires between specific terminal blocks and ground points. If the requisite wires are missing, they must be installed as per the specifications outlined in DeHavilland of Canada S.B No 6/473. The requirement is to comply with these directives before 31 July 1985, reflecting the urgency and critical nature of the electrical safety issues at hand. The geographic reach of these regulations extends throughout Australia, enforced by the Civil Aviation Safety Authority, ensuring adherence to safety standards across the Commonwealth.
Key Provisions
The Civil Aviation Regulations 1998, Part 39 - 105, specifically in relation to the Civil Aviation Safety Authority (CASA) Schedule of Airworthiness Directives for DHC-6 (Twin Otter) Series Aeroplanes, contains detailed operational requirements and obligations under AD/DHC-6/57 (paragraph 6/85). This Airworthiness Directive mandates an inspection of the Generator Field Control Relay Panel on all model DHC-6 Aircraft with Serial Numbers (S/Nos) ranging from 531 to 814, specifically post Modification No. 6/1590. The inspection must ascertain the presence of wires between Terminal Block TB-1A, Terminals A4 and C4, and Ground at intercostal C6FS1442-36. If the wires coded 1P80B20N and 2P80B20N are found between terminals A4 and C4 and ground, no further action is necessary. However, if these wires are absent, they must be installed in accordance with the specifications outlined in DeHavilland of Canada S.B No 6/473. The compliance deadline for these requirements was set as prior to 31 July 1985.
The obligations imposed by this Airworthiness Directive are clear and specific. Operators of DHC-6 (Twin Otter) Series Aeroplanes within the specified serial number range must ensure that the required inspections and installations are conducted. The inspection must be thorough, verifying the presence of the necessary ground wires. If the wires are missing, they must be installed correctly to prevent potential issues with the generator overvoltage protection system. This requirement ensures that the aircraft's electrical system operates safely and reliably, mitigating the risk of the generators entering a cyclic mode, which could lead to unsafe voltage fluctuations.
Failure to comply with the provisions of AD/DHC-6/57 (paragraph 6/85) can result in serious consequences. Although the specific penalties are not detailed within the text provided, non-compliance with Airworthiness Directives generally carries both civil and criminal liabilities under Australian aviation law. Civil penalties can include fines, while criminal penalties could involve imprisonment, depending on the severity of the breach and its impact on aviation safety. CASA has the authority to enforce these regulations, and non-compliance could also lead to the grounding of the aircraft until the necessary actions are taken to rectify the non-compliance, potentially disrupting operations and incurring additional costs for the operator.