AD/AC-SNOW/24 Amdt 5 Wing Spar (Cth)

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/AC-SNOW/24 Amdt 4 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.

Ayres Thrush (Snow) Commander Series Aeroplanes

AD/AC-SNOW/24 Amdt 5 Wing Spar 7/2006 DM

Applicability:

Models 600 S2D, S2R and S-2R series aircraft, as listed in FAA AD 2006-07-15 that do not have a part number 22507 lower spar cap incorporated on both the left and right wings.

Requirement:

Inspect the wing main spar lower caps in accordance with the technical requirements of FAA Corrected AD, 2006-07-15 Amdt 39-14542.

Note 1:  Ayres Service Bulletin No. SB-AG-39, Ayres Custom Kit No. CK-AG-29, and Quality Aerospace Custom Kit No. CK-AG-30 refers.

Note 2:  The Requirement document can be obtained through the FAA web site, or by contacting [email protected]

Compliance:

As specified in the Requirement document, with a revised effective date of
9 May 2006.

This Amendment becomes effective on 9 May 2006.

Background:

The original issue of this AD was raised following a wing spar fatigue failure accident in Holland, and initial inspections that found two Australian aircraft with cracked spars.

Amendment 1 was raised following a wing spar fatigue failure accident in the USA, the inspection results of the original AD issue revealing more aircraft with spar cracks, and a reassessment of compliance data.  The FAA issued an AD requiring a once-only inspection as an interim measure.  Both CASA and the Dutch authority, the RLD, instituted repetitive inspections.  Amendment 1 was subject to review upon receipt of further information.

Amendment 2 reflected the next FAA AD which took into account the service cracking experienced, and aircraft weight and configuration; and included repetitive inspections.

Amendment 3 retained the repetitive inspections and replacement (if necessary) requirements of the lower spar caps that are currently required by the previous AD, adds additional aircraft to applicability, and adds a third repair option.

Amendment 4 was issued as a result of FAA analysis of data from 112 cracks found in the last 8 years on similar design Model 600 S2D, S2R and S-2R series aircraft; and FAA’s determination that an immediate initial inspection and more frequent repetitive inspections are necessary for certain aircraft.  Consequently, this Directive requires an increase in frequency of the repetitive inspections for certain aircraft, and a decrease for others.  Undetected fatigue cracks could result in lower wing spar cap failure, and consequent loss of a wing.

Amendment 5 is issued in response to a revision of the related FAA AD, which corrects Table 3, (iii) Eddy Current Inspection, by moving “350 hours TIS” to the repetitive inspection interval third column.

David Villiers
Delegate of the Civil Aviation Safety Authority

5 May 2006