AIRWORTHINESS DIRECTIVE
On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/B737/297 Amdt 2 and issues the following 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 Amdt 3
De-Icing Fluids and Main Wheel
Well Electrical Connectors
1/2012
 
Applicability:
Model 737-600, -700, -700C, -800 and -900 series aeroplanes.
Despite the new AD/B737/297 Amdt 3, an exclusion or an alternate method of compliance that was in force before the coming into effect of AD/B737/297 Amdt 3 continues to be in force.

Requirement:
1.    Either

 
a.     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, or

 
b.    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.

 
2.    If, as a result of the Requirement 1.a. determination:

 
a.     It can be positively determined that an aeroplane has not been exposed, repeat Requirement 1.

 
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 the Requirement 1.b. inspection.

 
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 1.b. or 2.b. inspections in accordance with ASB 737-24A1148 Revision 1.

 
Inspections and/or rectifications accomplished before the effective date of the original issue 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.  Where equivalent inspections were required by either AD/B737/188 Amdt 1 or the original issue of this Directive, the interval for repetitive inspection in this Amendment commences when the last inspection was originally accomplished.

 
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.

 
FAA AMOC Letter 130S-09-9, issued to permit the use of a renamed corrosion inhibiting fluid, is 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 130S-05-490 dated 20 October 2005 refer.

Compliance:
For Requirement 1 - Within 12 months after the effective date of this Amendment and thereafter at intervals not exceeding 24 months.

 
For Requirement 2.a. - At intervals not exceeding 24 months after the initial determination.

 
For Requirement 2.b. - Within 90 days after the Requirement 1.a. determination is made and thereafter at intervals not exceeding 24 months.

 
For Requirement 3 - Before further flight after the Requirement 1.b. or 2.b. inspection, as applicable.

 
This Amendment becomes effective on 9 January 2012.

Background:
The original issue of this Directive superseded AD/B737/188 Amdt 1 (FAA AD 2002-16-03) which was cancelled.  AD/B737/188 Amdt 1 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.

 
 
 
 
The original issue of this Directive was 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.

 
The first Amendment followed clarification from the FAA that the inspection in paragraph (f) (2) of FAA AD 2005-18-23 (the AD on which this Directive is based) was indeed meant to be repetitive.  The Amendment also introduced the option to either make a determination regarding exposure to de-icing fluids or the carry out an inspection, again reflecting the requirements of the FAA AD.

 
The second Amendment was issued to correct a typographical error to the AMOC reference number.

 
The third Amendment incorporates FAA AMOC 130S-09-9 which allows a renamed inhibitor product to be used.  Following the acquisition of the original manufacturer, the new owners renamed the product range as a branding initiative.  Original product specifications remain unchanged and are compliant with the specifications detailed in the SB.

 
The original issue of this Directive became effective on 21 December 2006.

Mike Higgins
Delegate of the Civil Aviation Safety Authority
23 December 2011