AD/BELL 47/90 - Hydraulic Servo Cylinders

Overview

The Civil Aviation Regulations 1998, enacted by the Australian Parliament, provide comprehensive regulatory oversight of civil aviation within Australia. Specifically, Part 39 - 105 of the Regulations includes the Airworthiness Directives that ensure the continued safety of aircraft in operation. One such directive, AD/BELL 47/90, addresses the issue of hydraulic servo cylinder corrosion and binding in Bell Helicopter Textron 47 series helicopters, aiming to mitigate risks associated with potential failures in these critical components. This directive requires regular inspections and modifications to the hydraulic servo cylinders to prevent malfunctions that could compromise flight safety. The policy objective underpinning this directive is to maintain and enhance the safety standards of civil aviation by proactively addressing potential mechanical failures. The directive applies to all Bell 47 models equipped with specific hydraulic servo cylinders, mandating inspections for corrosion and verification of the input lever pivot bolts’ freedom of movement. If issues are detected, the servo must be removed from service for necessary repairs. Compliance with this directive is mandatory, with inspections required at specified intervals following the directive's issuance. This regulatory measure ensures that all relevant stakeholders, including pilots and licensed aircraft maintenance engineers, are aware of and adhere to the safety protocols designed to prevent hydraulic servo cylinder failures.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 105, addresses the safety directives concerning Bell Helicopter Textron 47 (All Variants) Series Helicopters, focusing on the hydraulic servo cylinders. This legislative instrument applies to all Bell 47 models that are equipped with hydraulic servo cylinders identified by part numbers 103650-3, 103650-5, and 47-691-273-1. The regulations mandate that inspections and necessary modifications must be carried out to ensure the airworthiness of these aircraft. Part 1 of the directive requires gaining access to the hydraulic servo cylinders, inspecting for corrosion, and verifying the freedom of the input lever pivot bolts by rotating them by hand, with appropriate action taken if stiffness or binding is detected. Part 2 mandates further inspection and modification of the servos in accordance with specified service bulletins, except for servo part number 47-691-273-1, which is exempt from these requirements. Compliance with these directives is essential and must be documented in the Maintenance Release. The inspection and certification can be performed by the pilot in command, a Licensed Aircraft Maintenance Engineer, or another authorised person, depending on the context and specific actions taken. These regulations are part of the broader Civil Aviation Regulations 1998, which are administered under the Civil Aviation Act 1988. The application of these regulations is overseen by the Civil Aviation Safety Authority, and they extend to all civil aviation activities within Australia, including territorial waters and airspace. This means that the directives apply to both domestic and international operations within the Australian jurisdiction. The Act does not specify any exclusions or exemptions for these directives, implying that all applicable aircraft must comply with the stipulated safety measures. Furthermore, the regulations can be extended or modified through subordinate instruments issued by the Civil Aviation Safety Authority.

Key Provisions

The Civil Aviation Regulations 1998, specifically Part 39 - 105, pertains to the airworthiness directives issued by the Civil Aviation Safety Authority (CASA). One such directive, AD/BELL 47/90, addresses the hydraulic servo cylinders of Bell Helicopter Textron 47 series helicopters. This directive applies to all Bell 47 models equipped with specific hydraulic servo cylinder part numbers (103650-3, 103650-5, and 47-691-273-1). The directive mandates that operators must ensure the hydraulic servo cylinders are inspected and maintained to prevent failures due to corrosion and binding. Under this directive, the primary requirement is to access the hydraulic servo cylinders and inspect them for signs of corrosion and verify the freedom of movement of the input lever pivot bolts. If any stiffness or binding is detected when rotating the bolts by hand, the bolts should be sprayed with a penetrating lubricant such as WD-40. If the condition persists, the servo must be removed from service and sent to an overhaul facility for necessary repairs or upgrades. Additionally, each servo must be inspected and, if necessary, modified in accordance with Flight Accessory Services Service Bulletin 004 Part A, except for servo part number 47-691-273-1, which is not subject to this modification requirement. Compliance with this directive is mandatory. Operators must conduct the inspection outlined in Part 1 of the directive at the next daily inspection after 28 November 1983, and subsequently at each daily inspection. For aircraft maintained under ANO 100.5.1, this directive must be logged on the Maintenance Release as maintenance required. The inspection outlined in Part 1 (a) and (b) can be performed by the pilot in command without needing certification, though certification can be done by a Licensed Aircraft Maintenance Engineer in other cases. Part 2 of the directive requires inspection and modification within the next 100 hours of time in service after 28 November 1983, but no later than 31 March 1984. Failure to comply with the provisions of this airworthiness directive can result in serious safety issues, as the manufacturer has reported a recent failure of the servo valve input rod assembly due to corrosion and binding. Operators are strongly advised to follow the directive closely to prevent potential accidents or malfunctions. Non-compliance may result in aircraft being deemed unairworthy, which could lead to severe penalties, including fines and potential grounding of the aircraft until the issues are rectified.