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/87 Wing Main Spar Steel Strap Corrosion 4/92 DM
Applicability: All 500, 600 and 700 series with the original factory-fitted internal steel strap which reinforces the main spar lower cap. The steel strap was fitted in aircraft serial numbers 1731 and subsequent, but not in the 690C and 695 series which featured an internal aluminium alloy strap.
Note: This excludes aircraft that have had the steel strap replaced, on the assumption that all replacement straps were 301 stainless.
Requirement: 1. Determine whether the strap is made from 4130 or 301 (stainless) steel. The following simple method is suggested.
Run a magnet along the wing lower surface skin, under the main spar, between the fuselage and the engine nacelle. If there is a strong magnetic attraction the strap is made from 4130 steel. Since the 4130 strap is prone to corrosion, it must be inspected in accordance with paragraph 2.
If there is no magnetic attraction the strap is made from 301 stainless steel, which is not as prone to corrosion, and does not have to be inspected. (Note that this does not obviate the need for the aluminium alloy spar caps to be inspected for corrosion under AD/AC/83).
2. Gain access to the 4130 steel strap inside the wing, removing fuel cells and lifting filler blocks as necessary. Visually inspect the exposed areas of the steel strap (in between the main spar lower cap and the next stringer aft) for corrosion, between the side of the fuselage and the engine nacelle.
If corrosion is found, determine the full extent of the corroded area on the remainder of the strap.
Protect the steel strap in the area opened up for inspection by liberally applying an inhibitor conforming to MIL-C-0081309C or MIL-C-16173D.
3. Inspect the seals on all upper surface access panels through which water may reach the steel strap. They should be water tight.
4. Report defects using the normal Major Defect reporting System and in addition organisations are requested to report the steel strap material and whether or not corrosion was found in the 4130 steel straps to Mr Dick Hewitt on (06) 268 4456.
Note: This aircraft has a history of wing fatigue problems. Repair of the steel strap, or the alloy spar cap, or any other primary structure, or continued flight with the defective straps on caps, must be supported by a though fatigue and residual strength evaluation.
Compliance: Complete the inspections not later than 31 March 1992. If micro structure of the main spar lower cap is susceptable to stress corrosion (AD/AC/86 refers) repair or replace the defective straps before further flight.
COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Background: Very severe corrosion has been found in the internal steel strap of an Australian- registered aircraft. The strap was made from 4130 steel, not 301 stainless as the design records indicate. Twin Commander has advised that there may be up to 200 other aircraft with 4130 steel straps, but there are unfortunately no production records. At least one corroded 4130 has be found in the USA.
The 4130 steel straps, unprotected, are very prone to corrosion. A corroded strap could seriously degrade the durability of the main spar assembly.
This Directive has been issued to protect the Australian fleet in the short term. Twin Commander are developing a more permanent solution, to be published in a forthcoming service bulletin.
Overview
The Commonwealth of Australia enacted the Civil Aviation Regulations 1998, with amendments over the years, to ensure the safety and efficiency of civil aviation in Australia. This legislation, overseen by the Civil Aviation Safety Authority, addresses the identification and rectification of safety issues in aircraft. One such issue pertains to the corrosion of steel straps in Twin Commander aircraft models 500, 600, and 700. Specifically, Airworthiness Directive AD/AC/87 targets the corrosion of the internal steel strap that reinforces the main spar lower cap in these aircraft, which can compromise the structural integrity of the wing. The directive was introduced to ensure that all applicable aircraft are inspected and, if necessary, repaired to prevent corrosion-induced failures. The policy objective is to maintain the airworthiness of the aircraft and protect the safety of passengers and crew.
Scope and Application
The Civil Aviation Regulations 1998, specifically Part 39 - 105, concerns the Airworthiness Directives for the Twin Commander (Gulfstream/Rockwell/Aerocommander 500, 600 and 700) series aeroplanes. This directive applies to all Twin Commander aircraft serial numbers 1731 and subsequent with the original factory-fitted internal steel strap that reinforces the main spar lower cap, excluding the 690C and 695 series which feature an internal aluminium alloy strap. The directive also excludes aircraft that have had the steel strap replaced, on the assumption that all replacement straps are 301 stainless. This regulation is a Commonwealth law and thus applies nationally across Australia, encompassing all relevant operators and entities within the aviation industry. Compliance is mandatory, and the inspection must be completed by 31 March 1992, with any necessary repairs or replacements of defective straps made before further flight if the microstructure of the main spar lower cap is susceptible to stress corrosion. This directive extends to requiring operators to report defects and specific findings about the steel strap material and corrosion presence to Mr Dick Hewitt.
Key Provisions
The Civil Aviation Regulations 1998, specifically under PART 39 - 105, establish critical airworthiness directives for the Twin Commander series aeroplanes. This particular directive (AD/AC/87) pertains to the corrosion of the wing main spar steel strap in 500, 600, and 700 series aircraft equipped with the original factory-fitted internal steel strap (section 1). The directive applies to aircraft with serial numbers 1731 and subsequent, excluding the 690C and 695 series which have internal aluminium alloy straps (section 2).
The directive mandates that operators determine whether the steel strap is made of 4130 or 301 (stainless) steel by using a magnet to test for magnetic attraction (section 3). If the strap is made of 4130 steel, it must undergo a detailed inspection for corrosion, which includes removing fuel cells and lifting filler blocks as necessary to gain access to the strap (section 4). The inspection involves visually checking the exposed areas of the steel strap and applying an inhibitor to any corroded areas (section 5). Additionally, operators must inspect the seals on all upper surface access panels to ensure they are watertight (section 6). Any defects identified must be reported through the normal Major Defect reporting System, and additional information about the steel strap material and the presence of corrosion must be communicated to Mr Dick Hewitt (section 7).
Operators of these aircraft are obligated to complete the required inspections by 31 March 1992. If the microstructure of the main spar lower cap is susceptible to stress corrosion, as referenced in AD/AC/86, the defective straps must be repaired or replaced before any further flight (section 8). Failure to comply with these directives can result in serious safety risks, including the potential for wing fatigue problems, which could compromise the structural integrity of the aircraft.
The Civil Aviation Regulations impose strict penalties for non-compliance with these airworthiness directives. Any breaches of these requirements can result in significant civil or criminal consequences. The specific penalties are not detailed in the text, but they can include fines, suspension of airworthiness certificates, or other regulatory actions that may further escalate to criminal charges in cases of gross negligence or willful disregard for safety protocols. The seriousness of these consequences underscores the importance of adhering to the specified inspection and maintenance procedures to ensure the safety and airworthiness of the affected aircraft.