AD/Hu 369/121 Amdt 2 Vertical Stabilizer Control System Adapter Tubes (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/HU 369/121 Amdt 1 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.

McDonnell Douglas (Hughes) and Kawasaki 369 Series Helicopters

AD/HU 369/121 Amdt 2 Vertical Stabilizer Control System
Adapter Tubes 13/2008 TX

Applicability:

Model 500N and Model 600N helicopters, with Yaw Stability Augmentation System (YSAS) adapter tubes, part number (P/N) 500N7218-1, installed.

Requirement:

1.    Turn the YSAS switch OFF.

Note 1:  MDHI Service Bulletin SB500N-040R1/SB600N-047R1 dated 27 August 2008, MDHI maintenance manual CSP-HMI-3, Section 96-00-00, pertain to the subject of this AD.

Note 2:  The original issue of this AD required the CB to be pulled and collared.  Ensure that the CB is un-collared and reset.

2.    Install a placard on the instrument panel as close as practicable to the airspeed indicator that states:

“YSAS SYSTEM IS OFF.  AIRPSEED LIMIT 100 KIAS or V_NE, WHICHEVER IS LESS.”

3.    Make pen and ink changes or place a copy of this AD in the airworthiness limitations section of the Rotorcraft Flight Manual (RFM) to revise the airworthiness limitations as follows:

“V_NE is limited to 100 KIAS or less as determined by referring to the airspeed V_NE placard already installed on the helicopter.”

4.    Replace each adaptor tube with an airworthy adaptor tube that has a production date code.

Remove the placards and revisions that were made to the RFM and return the YSAS switch to its normal position.

The replacement of the adaptor tube with an airworthy adaptor tube that has a production date code stamp is terminating action for the requirements of this AD.

Note 3:  FAA Emergency AD 2008-22-52 refers.  This AD supersedes FAA Emergency AD 2008-18-52.

Compliance:

For Requirements 1, 2 and 3 - Before further flight.

For Requirement 4 - Within 45 days after the effective date of this AD.

This Amendment becomes effective on 27 October 2008.

Background:

This Airworthiness Directive was prompted by reports that two Model MD900 helicopters experienced broken Vertical Stabilizer Control System (VSCS) adapter tubes.  In one case, the helicopter experienced uncommanded yaw, resulting in loss of a window and a door.  The same part-numbered adapter tube is used on the Model 500N and 600N helicopters Yaw Stability Augmentation System (YSAS).  Some of the VSCS and YSAS adapter tubes were not manufactured to the required specifications and can fail.  This condition, if not corrected, could result in loss of yaw control and subsequent loss of control of the helicopter.

Amendment 1 was raised in response to the FAA being advised that the action of pulling the CB can result in impaired directional control which could result in loss of control of the helicopter.  Therefore amendment 1 required that the YSAS is turned off instead of pulling the CB.

Amendment 2 removes reference to any serial numbers in the applicability section because the unsafe condition can occur on any helicopter with the affected tubes installed.  This amendment also requires that replacement adaptor tubes have a production date code stamped on them to determine that the parts are airworthy. (e.g., 08-08 indicates a production date of August 2008).

The original issue of this AD became effective on 26 August 2008.

Amendment 1 of this AD became effective 28 August 2008.

James Coyne
Delegate of the Civil Aviation Safety Authority

24 October 2008