AD/At/20 Amdt 4 Wing Lower Spar Cap Safe Life (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/AT/20 Amdt 3 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.

Airtractor AT-300, 400 and 500 Series Aeroplanes

AD/AT/20 Amdt 4 Wing Lower Spar Cap Safe Life 7/2006 DM

Applicability:

Model AT-501 aircraft.

Requirement:

Action in accordance with the technical requirements of FAA AD 2002-11-05 R1 Amdt 39-14564.

Compliance:

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

This Amendment becomes effective on 5 May 2006.

Background:

An AT-502A aircraft in Arizona suffered an in-flight wing fatigue failure in April 2000.  Service Letter No. 197 and FAA AD 2000-14-51 address the problem by specifying repetitive visual or ultrasonic inspection of the critical location in the wing spars of certain early production aircraft, until terminating wing spar reinforcement modification is installed.

Amendment 1 was prompted by numerous reports of cracks found in the 3/8-inch bolt hole of the wing lower spar cap on the affected aircraft.  The required actions are intended to prevent fatigue cracks from occurring in the wing lower spar cap before the originally established safe life limit is reached.  Fatigue cracks, not detected and corrected, could result in in-flight separation of the wing.

Amendment 2 allowed modification of the wing lower spar cap, rather than just replacement, upon reaching the safe life limit.

Amendment 3 retained the safe life for the wing lower spar cap for affected aircraft that was previously established, and reduced the safe life for aircraft that incorporate or have incorporated Marburger Enterprises Inc. winglets.  This Directive also required an eddy current inspection immediately prior to the replacement/modification to detect and correct any crack in a bolthole before it extends to the modified centre section of the wing.  This Directive was the result of reports the FAA received of cracks originating in the outboard 3/8-inch hole of the main spar lower cap on affected aircraft at times lower than the established safe life.

Amendment 4 is issued in response to a revision of the related FAA AD, which retains the actions of the previous issue of this Directive for Model AT-501 aircraft, and removes AT-400 series and Models AT-802 and AT-802A aircraft from applicability.  The requirements for AT-400 series aircraft are now contained in AD/AT/27 and the requirements for Models AT-802 and AT-802A aircraft are now contained in AD/AT 800/7.

David Villiers
Delegate of the Civil Aviation Safety Authority

3 May 2006