AD/Hu 369/116 Lateral Mixer Output Link Assembly (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 369/116 Lateral Mixer Output Link Assembly 4/2007

Applicability:

Model MD600N helicopters, with a lateral mixer output link assembly part number 600N7636-1, -3, -9 or -11, installed.

Requirement:

1.    Remove each lateral mixer output link assembly (mixer link) and visually inspect, with a bright light and a 10x or higher magnifying glass, for cracks in the shaded areas around the bearing bore as depicted in the following Figure 1:

Figure 1

2.    Perform an eddy current inspection of each mixer link in the bearing end areas.

Replace any cracked mixer link with a serviceable mixer link on which an eddy current inspection has been performed.

Perform an eddy current inspection on each mixer link before installation on any helicopter.

Note:  FAA Emergency AD 2007-05-51 and MDHI Service Bulletin No. SB600N-044 refer.

Compliance:

Before further flight.

This Airworthiness Directive becomes effective on 12 April 2007.

Background: The FAA received a report of a cracked lateral mixer output link assembly part number 600N7636-1, on an in-service MDHI Model MD600N helicopter.  Cracks were also detected on two additional mixer links part number 600N7636-3, which were being held as spares.  The cracks on all three mixer links run through the bearing end area of the mixer link and emanate from staking marks in the mixer link.  Undetected cracks in the mixer link could result in failure of the mixer link and subsequent loss of control of the helicopter.

David Villiers
Delegate of the Civil Aviation Safety Authority

28 February 2007