AD/DHC-8/29 - Anti-Collision Strobe Light Power Supplies

Overview

The Civil Aviation Regulations 1998, enacted by the Australian Parliament, encompass a range of safety standards and directives to ensure the safe operation of aircraft within Australian airspace. One such directive is the Airworthiness Directive DHC-8/29, which was introduced to address specific safety issues related to Bombardier (Boeing Canada/De Havilland) DHC-8 Series aeroplanes. This directive focuses on the anti-collision strobe light power supplies for DHC-8 Series 100 and 300 aircraft, aiming to mitigate risks associated with electromagnetic interference that could adversely affect the operation of critical systems. The directive mandates compliance with specific modifications and service bulletins issued by the manufacturer to ensure the safety of these aircraft, thereby aligning with the overarching policy objective of maintaining high safety standards in civil aviation.

Scope and Application

The Civil Aviation Regulations 1998, as amended, apply to the DHC-8 Series 100 and 300 aircraft with specific serial numbers that do not have Modification 8/1273 incorporated. The regulations mandate that these aircraft must adhere to the Airworthiness Directive AD/DHC-8/29 concerning anti-collision strobe light power supplies. This directive requires the incorporation of Modification 8/1273 in accordance with Bombardier Regional Aircraft Division de Havilland Dash 8 Service Bulletin 8-33-19 Revision A dated 31 May 1993. The directive further specifies compliance actions, including performing the required modifications before further flight after 6 September 1993 if certain faults are present, or prior to 31 March 1994 if no such faults have been experienced. The purpose of this directive is to mitigate the risk of electromagnetic interference causing incorrect operation of the proximity switch electronics unit, which can lead to several operational issues such as erratic landing gear advisory lights, cabin pressurisation fluctuations, and compromised ground operations.

Key Provisions

The Civil Aviation Safety Authority (CASA) has issued an Airworthiness Directive (AD) under the Civil Aviation Regulations 1998, specifically targeting Bombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes (sections 39-105). This AD, designated AD/DHC-8/29, pertains to the anti-collision strobe light power supplies of DHC-8 Series 100 and 300 aircraft with serial numbers 3 through 214 inclusive, excluding those that have already incorporated Modification 8/1273. The directive requires two main actions. Firstly, operators must follow the instructions outlined in Part B of the Accomplishment Instructions in the Bombardier Regional Aircraft Division de Havilland Dash 8 Alert Service Bulletin A8-33-33 dated 31 May 1993 (section 39-105). Secondly, they must incorporate Modification 8/1273 as per Bombardier Regional Aircraft Division de Havilland Dash 8 Service Bulletin 8-33-19 Revision A, also dated 31 May 1993 (section 39-105). Operators of the affected aircraft must adhere to specific compliance requirements. Before any further flight after 6 September 1993, operators must address any faults indicated by continuous or intermittent illumination of the landing gear green locked down advisory lights when the landing gear is up and locked, or when the landing gear is down and locked prior to or after landing. Additionally, operators must rectify these faults before 31 March 1994 if the aircraft have not yet incorporated Modification 8/1273. The incorporation of this modification is considered the completion of the maintenance actions required by the directive. Failure to comply with the AD/DHC-8/29 could lead to significant operational issues and safety risks. The directive notes that the anti-collision light power supply units may develop a fault causing strong parasitic electromagnetic emissions. These emissions can adversely affect the proximity switch electronics unit (PSEU), resulting in incorrect operations such as flashing of the landing gear locked down advisory lights during cruise, fluctuation of the cabin pressurisation rate needle, retraction and extension of roll and ground spoilers during ground operation, inoperative nose gear steering after landing, and unavailability of normal wheel brakes below 35-40 knots. Ensuring compliance with this directive is essential to prevent such malfunctions and maintain the airworthiness of the aircraft.