AD/B737/297 De-Icing Fluids and Main Wheel Well Electrical Connectors (Cth)

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 39.001(1) of CASR 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 737 Series Aeroplanes

AD/B737/297 De-Icing Fluids and Main Wheel
Well Electrical Connectors 13/2006

Applicability:	Model 737-600, -700, -700C, -800 and -900 series aeroplanes.
Requirement:	1.    Determine aeroplane exposure to runway de-icing fluids containing potassium formate or potassium acetate by reviewing airport data on the type of components in the de-icing fluid used at airports that support aeroplane operations.
2.    If, as a result of the Requirement 1 determination:
a.     It can be positively determined that an aeroplane has not been exposed repeat the Requirement 1 determination at 24 monthly intervals.
b.    It can be determined that an aeroplane has been exposed or it cannot be conclusively determined that an aeroplane has not been exposed, perform a detailed inspection of the line replaceable units (LRU) electrical connectors (including the contacts and backshells) in the wheel well of the main landing gear (MLG) for corrosion (the presence of moisture, corrosion pits, or white coloured material build-up), in accordance with Boeing Alert Service Bulletin (ASB) 737-24A1148 Revision 1 dated 10 July 2003.
Note 1:  For the purposes of this Directive, a detailed inspection is defined as: "An intensive visual examination of a specific structural area, system, installation or assembly to detect damage, failure or irregularity.  Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector.  Inspection aids such as mirror, magnifying lenses, etc., may be used.  Surface cleaning and elaborate access procedures may be required."
3.    Rectify any discrepancies noted during the Requirement 2 inspection in accordance with ASB 737-24A1148 Revision 1.
Inspections and/or rectifications accomplished before the effective date of this Directive in accordance with the Accomplishment Instructions of ASB 737-24A1148, dated 6 December 2001, are acceptable for compliance with this equivalent requirements of this Directive.
Later revisions of the above SB, approved by the United States Federal Aviation Administration (FAA) as an Alternate Method of Compliance (AMOC) to FAA AD 2005-18-23, are considered acceptable for compliance with the equivalent requirements of this Directive.
Note 2:  FAA AD 2005-18-23 Amdt 39-14264 and FAA AMOC Letter 103S-05-490 dated 20 October 2005 refer.
Compliance:	For Requirement 1 - Within 12 months after the effective date of this Directive and thereafter at intervals not exceeding 24 months.
For Requirement 2.b. - Either within 90 days after the Requirement 1 determination or within 24 months after the last inspection in accordance with AD/B737/188 Amdt 1 and thereafter at intervals not exceeding 24 months.
For Requirement 3 - Before further flight after the Requirement 2.b. inspection.
This Airworthiness Directive becomes effective on 21 December 2006.
Background:	This Directive supersedes AD/B737/188 Amdt 1 (FAA AD 2002-16-03) which is cancelled.  That Directive required either determining exposure to runway de-icing fluids containing potassium formate, or performing inspections of certain electrical connectors in the wheel well of the main landing gear (MLG) for corrosion and follow-on actions.  This new Directive adds a new inspection requirement and related corrective actions.
The Directive is issued to prevent corrosion and subsequent moisture ingress into the electrical connectors, which could result in an electrical short and consequent incorrect functioning of critical aeroplane systems essential to safe flight and landing of the aeroplane, including fire warning systems.

James Coyne
Delegate of the Civil Aviation Safety Authority

25 October 2006