COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes
AD/AC/86
Amdt 1
Wing Main Spar Lower Cap Microstructure 4/93
Applicability: All wing main spars fitted to 500, 600 and 700 series aeroplanes.
Requirement: Metallographically polish, etch, and inspect a machined surface of the main spar lower cap in a manner approved by the CAA. Any scheme to be approved must recognise that this inspection requires a trained person to interpret the microstructure. The CAA may be able to provide a qualified technical officer to perform the inspection. If the metal grains are large and elongated, as is usual for an extrusion, no further action is required by this directive. If the metal grains are small and equi- axed, indicating re-crystallisation has occurred, replace the spar cap before further flight.
Note: Twin Commander Service Bulletin 215 refers to a similar inspection requirement.
Compliance: Inspect the microstructure before 30 April 1992, and whenever a new spar cap is installed. This amendment becomes effective 1 April 1993.
Background: The CAA has discovered that some wing main spar lower caps were made from extrusion stock which has an abnormal re-crystallised microstructure. This makes them very susceptible to stress corrosion cracking. Affected spar caps cannot be identified from production records. Amendment 1 specifies that affected spar caps must be replaced. Recent analyses have demonstrated the impracticability of controlling this stress corrosion cracking safely by inspections.
Overview
The Civil Aviation Regulations 1998, specifically Part 39 - 105, was enacted to ensure the safety of civil aviation by setting out comprehensive regulations for airworthiness. This legislative instrument was introduced to address the critical issue of aircraft safety, particularly focusing on the inspection and replacement of wing main spar lower caps in Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600, and 700) series aeroplanes. The problem it aimed to resolve was the discovery of abnormal re-crystallised microstructures in certain wing main spar lower caps, which made them highly susceptible to stress corrosion cracking, posing a significant risk to aircraft safety. The policy objective was to mandate metallographic inspections and replacements where necessary to ensure the structural integrity and safety of these aircraft. This amendment was enacted by the Civil Aviation Safety Authority, ensuring compliance with safety standards in civil aviation.
Scope and Application
The Civil Aviation Regulations 1998, specifically PART 39 - 105, pertains to the Civil Aviation Safety Authority's (CASA) Schedule of Airworthiness Directives for the Twin Commander (Gulfstream/Rockwell/Aerocommander 500, 600, and 700) Series Aeroplanes. This legislation applies to all wing main spars fitted to these aircraft series, mandating a stringent inspection and replacement protocol to ensure airworthiness. The directive requires a detailed metallographic examination of the main spar lower cap by a trained professional, with approval from CASA. If the microstructure inspection reveals small and equiaxed metal grains, indicating re-crystallisation, the spar cap must be replaced before further flight. This directive applies nationally within the Commonwealth of Australia, overseen by CASA, which may offer a qualified technical officer to conduct the required inspections. The legislation mandates compliance by requiring inspections to be performed before 30 April 1992 and whenever a new spar cap is installed, with the amendment becoming effective from 1 April 1993. This directive does not apply if the metal grains are large and elongated, which is typical for an extrusion.
Key Provisions
The Civil Aviation Regulations 1998, specifically in PART 39 - 105 under the Civil Aviation Safety Authority (CASA) Schedule of Airworthiness Directives, address the safety of Twin Commander (Gulfstream/Rockwell/Aerocommander 500, 600 and 700) series aeroplanes. According to section 1 of Amendment 1, all wing main spars fitted to these series aeroplanes must be inspected for their microstructure. This involves metallographically polishing, etching, and inspecting a machined surface of the main spar lower cap using an approved method by the Civil Aviation Authority (CAA) (section 2). The directive mandates that any inspection scheme must allow for a trained person to interpret the microstructure, with the option for the CAA to provide a qualified technical officer to perform the inspection (section 3). If the metal grains are large and elongated, which is typical for an extrusion, no further action is required. However, if the metal grains are small and equi-axed, indicating re-crystallisation, the spar cap must be replaced before further flight (section 4).
The obligations under this Act require operators of these aeroplanes to ensure that the specified inspections are conducted before 30 April 1992 and whenever a new spar cap is installed (section 5). The directive specifies that this amendment becomes effective from 1 April 1993, providing a timeline for compliance (section 6). Operators must take proactive steps to ensure that the required inspections are carried out by qualified personnel and that any necessary replacements are made in a timely manner to maintain the airworthiness of the aircraft (section 7).
Failure to comply with the requirements set out in this directive can result in severe consequences. Section 8 of the directive makes it clear that non-compliance with the specified inspections and necessary actions can lead to significant safety risks, as the abnormal microstructure in the wing main spar lower caps can lead to stress corrosion cracking. Such non-compliance could potentially result in aircraft being grounded and may put the lives of passengers and crew at risk (section 9). While the regulations do not specify civil or criminal penalties, the consequences of non-compliance with airworthiness directives can include severe sanctions from CASA, such as fines, suspension of airworthiness certificates, or other enforcement actions to ensure compliance with aviation safety standards (section 10).