AIRWORTHINESS DIRECTIVE AIRWORTHINESS DIRECTIVE

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/ AD/B747/252 Pitot Static Probe Wiring 8/2001

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.