AD/B747/149 - Fuselage Skin Above Forward Entry Doors

Overview

The Civil Aviation Regulations 1998, specifically Part 39, includes a series of Airworthiness Directives aimed at ensuring the safe operation of aircraft within Australian airspace. One such directive, AD/B747/149, addresses specific concerns about the fuselage skin of Boeing 747 Series aeroplanes, particularly around the forward entry doors. This directive was enacted to address the problem of skin cracks reported by operators, which, if left unrepaired, could lead to rapid decompression. The directive requires inspections and modifications to specific sections of the aircraft to mitigate these risks. This AD was issued by the Civil Aviation Safety Authority under the authority granted by the Civil Aviation Act 1988 and is intended to ensure that aircraft meet the required safety standards. The underlying policy objective is to enhance the safety of air travel by preemptively addressing structural issues that could compromise the integrity of the aircraft.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 105 and the Civil Aviation Safety Authority Schedule of Airworthiness Directives for Boeing 747 Series Aeroplanes, applies to all Boeing 747 aircraft within line numbers 1 to 206 inclusive. The directive mandates inspections and modifications to the fuselage skin above the forward entry doors to address potential skin cracks that could lead to rapid decompression. Operators must inspect the specified areas using the high-frequency eddy current method and comply with the Boeing Service Bulletins referenced in the directive. For aircraft not previously modified under certain service bulletins, additional inspections are required. Compliance necessitates inspections before a specific number of flights and at intervals thereafter, while modifications must be completed before a certain number of flights, with compliance to modifications cancelling the need for further inspections. This directive extends to all Boeing 747 aircraft within the specified line numbers and ensures safety standards are met through detailed inspection and modification procedures.

Key Provisions

The Civil Aviation Regulations 1998, specifically Part 39 - 105, under the Civil Aviation Safety Authority's Schedule of Airworthiness Directives for Boeing 747 series aeroplanes, mandates detailed inspections and modifications for the fuselage skin above the forward entry doors. According to AD/B747/149 (Section 1), operators of Boeing 747 aircraft, line numbers 1 to 206 inclusive, must inspect the fuselage skin at the aft row of fasteners between stringers S-14E and S-16 at the left and right Body Station (BS) 460 circumferential splice for cracks. This inspection must be conducted using the high-frequency eddy current (HFEC) method in accordance with Boeing Service Bulletin (SB) 747-53-2289, Revision 2. For aircraft that have not been modified as per Boeing SB 747-53-2181 or SB 747-53-2105, an additional HFEC inspection of the forward row of fasteners of the BS 460 circumferential splice is required, again in accordance with Boeing SB 747-53-2289, Revision 2. Furthermore, operators must modify the aft side of the left-hand and right-hand lap splices between stringers 14E and 16 in accordance with Boeing SB 747-53-2289, Revision 2. If not previously done, they must also modify the forward side of the left-hand and right-hand lap splices between stringers 14E and 16 in accordance with either Boeing SB 747-53-2181 or SB 747-53-2105. Operators must comply with specific timelines for inspections and modifications as outlined in the directive. The initial inspection must be performed before the aircraft accumulates 10,000 flights or before 1,000 flights after 22 June 1995, whichever occurs last. Subsequent inspections must be conducted at intervals not exceeding 3,000 flights (Section 2). The required modifications must be completed before the aircraft accumulates 20,000 flights. It is important to note that if the modifications are performed, the inspection requirements specified in this directive are negated. Failure to comply with the AD/B747/149 provisions can result in significant safety risks, as the regulation is in response to numerous reports of skin cracks up to 15 inches long at the rear fastener row of the BS 460 circumferential skin splice. If these cracks remain unrepaired, they could lead to rapid decompression. The requirements of this airworthiness directive are consistent with the recommendations of the Boeing 747 Structures Working Group. Non-compliance could potentially lead to serious safety incidents and legal repercussions for the operators, as the AD is designed to mitigate these risks.