AIRWORTHINESS DIRECTIVE
For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.
Boeing 747 Series Aeroplanes
AD/B747/252 Pitot Static Probe Wiring 8/2001
Applicability: Model 747-400 series airplanes, as listed in Boeing Alert Service Bulletin (ASB) 747- 30A2078, Revision 1, dated 16 November 2000.
Requirement: 1. Perform a special detailed inspection to detect miswiring of diodes in the heating system of the pitot static probes in accordance with ASB 747-30A2078, Revision 1.
Inspections accomplished prior to the effective date of this Directive in accordance with ASB 747-30A2078, dated 24 August 2000, are acceptable for compliance with the action specified in Requirement 1.
2. If any miswiring is found during the Requirement 1 inspection, rewire per Boeing 747-400 Wiring Diagrams 30-31-11 and 30-31-21, as referenced in ASB 747- 30A2078, Revision 1.
Note 1: For the purposes of this Directive, a special detailed inspection is defined as: “An intensive examination of a specific item(s), installation, or assembly to detect damage, failure, or irregularity. The examination is likely to make extensive use of specialized inspection techniques and/or equipment. Intricate cleaning and substantial access or disassembly procedures may be required.”
Note 2: FAA AD 2001-12-14 Amdt 39-12269 refers.
Compliance: For Requirement 1 - Within 15 months after the effective date of this Directive.
For Requirement 2 - Before further flight after the Requirement 1 inspection. This Airworthiness Directive becomes effective on 9 August 2001.
Background: Boeing advised that several operators reported burnt diodes in the Pitot Probe Heat System. The cause of the anomalies was determined to be miswiring of the diodes in the power reduction circuitry. Reduced power to the heating system of the pitot static probes could lead to ice accumulation on the pitot static probes. Ice accumulation may result in erroneous airspeed or altitude indications to the flight crew, and consequent reduced safety of flight.
Boeing 747 Series Aeroplanes
AD/B747/252 (Continued)
This Directive requires an inspection to detect miswiring of diodes in the heating system of the pitot static probes and, if necessary, corrective action.
Eugene Paul Holzapfel
Delegate of the Civil Aviation Safety Authority 29 June 2001
The above AD is notified in the Commonwealth of Australia Gazette on 11 July 2001.
Overview
The Airworthiness Directive (AD) for Boeing 747 Series Aeroplanes, specifically AD/B747/252, was introduced in 2001 to address a safety concern identified with the pitot static probe wiring of the Boeing 747-400 series aircraft. This directive was issued by the Civil Aviation Safety Authority (CASA) under the Civil Aviation Regulations 1998. The problem identified was the miswiring of diodes in the heating system of the pitot static probes, which could lead to ice accumulation on the probes, resulting in erroneous airspeed or altitude indications to the flight crew and consequently reducing the safety of flight. The policy objective of the AD is to ensure that the unsafe condition is corrected by requiring a detailed inspection and, if necessary, corrective action to be taken on the specified aircraft models.
Scope and Application
The Airworthiness Directive issued by the Civil Aviation Safety Authority (CASA) applies specifically to the Boeing 747-400 series aeroplanes as identified in Boeing Alert Service Bulletin (ASB) 747-30A2078, Revision 1, dated 16 November 2000. The directive mandates a special detailed inspection to detect any miswiring of diodes in the heating system of the pitot static probes, in accordance with the specified bulletin. If any miswiring is identified during this inspection, corrective rewiring must be performed in line with Boeing 747-400 Wiring Diagrams 30-31-11 and 30-31-21 as referenced in the bulletin. The directive applies nationally within Australia, with its effective date set as 9 August 2001. This directive is issued under the authority of the Civil Aviation Regulations 1998, which allow for the creation of such airworthiness directives to address safety concerns. Compliance with this directive is mandatory for all applicable aircraft within the specified timeframes outlined in the directive.
Key Provisions
The Airworthiness Directive (AD) AD/B747/252 issued by the Civil Aviation Safety Authority (CASA) pertains specifically to Model 747-400 series aeroplanes. The AD mandates a special detailed inspection to detect any miswiring of diodes in the heating system of the pitot static probes, as outlined in Boeing Alert Service Bulletin (ASB) 747-30A2078, Revision 1. This inspection is necessary to address the potential unsafe condition arising from miswiring, which can lead to ice accumulation on the probes, thereby affecting airspeed and altitude readings. The AD specifies that inspections conducted prior to the effective date of this directive, in accordance with ASB 747-30A2078 dated 24 August 2000, are acceptable for compliance with the directive.
Operators of the Model 747-400 series aeroplanes are obligated to perform the required inspection within 15 months of the directive’s effective date. Should the inspection reveal any miswiring, the directive requires immediate corrective action to rewire the system according to Boeing 747-400 Wiring Diagrams 30-31-11 and 30-31-21, as referenced in ASB 747-30A2078, Revision 1. This corrective action must be completed before any further flight is undertaken after the inspection. The AD also provides a definition of what constitutes a special detailed inspection, which is an intensive examination aimed at detecting damage, failure, or irregularity using specialized techniques and equipment.
Failure to comply with the requirements of this AD can lead to serious consequences for the safety of the aircraft and its occupants. The AD does not explicitly outline penalties for non-compliance but implies that any failure to adhere to these safety measures could result in unsafe flight conditions, potentially leading to accidents or incidents. The CASA delegate’s authority under subregulation 39.1(1) of the Civil Aviation Regulations 1998 implies that enforcement actions could be taken against non-compliant operators, although the exact penalties are not specified in the AD itself.