AD/Hu 369/121 Vertical Stabilizer Control System Adapter Tubes (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.

McDonnell Douglas (Hughes) and Kawasaki 369 Series Helicopters

AD/HU 369/121 Vertical Stabilizer Control System Adapter Tubes 11/2008 TX

Applicability:

Model 500N helicopters, serial numbers (S/N) -001 through -107 with a prefix of “LN,” and Model 600N helicopters, S/N -003 through -076 with a prefix of “RN,” with Yaw Stability Augmentation System (YSAS) adapter tubes, part number (P/N) 500N7218-1, installed.

Requirement:

1.    De-energize the YSAS, pull the circuit breaker on the circuit breaker panel, and install a plastic cable tie on the circuit breaker to prevent accidental operation of the YSAS.

Note 1:  MDHI maintenance manual CSP-HMI-3, Section 96-00-00, pertains to the subject of this AD.

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

“YSAS SYSTEM DE-ENERGIZED. AIRPSEED LIMIT 100 KIAS or VNE, 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:

(a)   VNE is limited to 100 KIAS or less as determined by referring to the airspeed VNE placard already installed on the helicopter.

(b)   Use of the autopilot is prohibited.

Note 2:  FAA Emergency AD 2008-18-51 dated 20 August 2008 refers.

Compliance:

Before further flight after the effective date of this AD.

This Airworthiness Directive becomes effective on 26 August 2008.

Background:

This Airworthiness Directive is 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.

The manufacturer anticipates having airworthy YSAS and VSCS adapter tubes available within the next 30 to 60 days.  It is also anticipated that an amendment to this AD, will be made, requiring that the YSAS and VSCS adapter tubes be replaced with the airworthy parts as a terminating action to the requirements of this AD.

David Villiers
Delegate of the Civil Aviation Safety Authority

22 August 2008