Ad/SF340/108 - Hydraulic System Accumulators (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.

SAAB SF340 Series Aeroplanes

AD/SF340/108 Hydraulic System Accumulators 10/2008

Applicability:

SAAB AB, SAAB Aerosystems (formerly SAAB Aircraft AB) SF340A and 340B aircraft, which have hydraulic accumulators Part Number (P/N) 08 8423 001 1 or P/N 08 8423 030 1 installed, except accumulators with serial numbers as listed in SAAB Service Bulletin (SB) 340-29-023 dated 10 June 2008.

Requirement:

1.    Replace hydraulic accumulators P/N 08 8423 001 1 and P/N 08 8423 030 1 (except those with serial numbers as listed in SAAB SB 340-29-023) with a new or modified accumulator in accordance with SAAB SB 340-29-023 or later approved revision.

2.    Do not install a hydraulic accumulator with P/N 08 8423 001 1 or P/N
08 8423 030 1 on any aircraft, except those with serial numbers as listed in SAAB SB 340-29-023 or later approved revision.

Note:  EASA AD 2008-0146 dated 1 August 2008 refers.

Compliance:

For Requirement 1

For accumulators having a manufacturing date of June 2000 or earlier - Within 24 months after the effective date of this AD.

For accumulators having a manufacturing date of July 2000 or later - Within 10 years from the manufacturing date or within 24 months after the effective date of this AD, whichever occurs later after the effective date of this AD.

For Requirement 2 - After 15 August 2010.

This Airworthiness Directive becomes effective on 25 September 2008.

Background:

Two cases of main hydraulic accumulator failure have been reported, one of which was caused by corrosion.  Investigation has shown that a severe failure can occur to any of the four hydraulic accumulators which are installed in the hydraulic compartment.  Either one of the two end parts on the accumulator may depart from the pressure vessel due to corrosion.  This condition, if not corrected, is likely to degrade the functionality of the hydraulic system, possibly resulting in degradation or total loss of control of the landing gear, flap actuation and brakes.

A severe failure during flight may even result in debris penetrating and exiting the fuselage outer skin.  When such a failure occurs while the aircraft is on the ground, as in the two reported cases, this may cause severe damage to the fuselage and result in injuries to persons nearby.

To address and correct the unsafe condition, a modified hydraulic accumulator has been developed, which is sealed between the barrel and the screw cap and between the screw cap and the end cap.

For the reasons described above, this AD requires the replacement of the affected hydraulic accumulators P/N 08 8423 001 1 and P/N 08 8423 030 1, as identified in SAAB SB 340-29-023, with a modified hydraulic accumulator.

James Coyne
Delegate of the Civil Aviation Safety Authority

8 August 2008