AD/Do 228/11 Honeywell Cas 67a ACAS II LBA STC SA1310 (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.

Dornier 228 Series Aeroplanes

AD/DO 228/11 Honeywell CAS 67A ACAS II - LBA STC SA1310 5/2007

Applicability:	Model 228-100, 228-101, 228-200, 228-201 and 228-212 aeroplanes, all serial numbers except 8191, 8232, 8233, 8244 and 8245, modified in accordance with Luftfahrtbundesamt (LBA) Supplemental Type Certificate (STC) No.SA1310 before 31 January 2005.
Requirement:	Modify the Honeywell CAS67A Airborne Collision Avoidance System (ACAS) II, installed under LBA STC SA1310, in accordance with Aerotechnic Vertriebs und Service GmbH Service Bulletin DO228-119780-0104 Revision 2 dated 21 December 2006.
Note:  EASA AD 2007-0059 refers.
Compliance:	Within 200 flight cycles or 8 weeks, whichever comes first, after the effective date of this Directive.
This Airworthiness Directive becomes effective on 10 May 2007.
Background:	The European Aviation Safety Agency (EASA) has received advice from the STC holder that in earlier installations of the ACAS II system there were no isolation diodes installed in the heading and attitude valid lines.  The absence of an isolation diode in the valid lines can prevent the valid flag to come up even if a gyro fault exists.  The problem has only been detected for heading valid lines but could equally affect the attitude valid lines.
With installation of the ACAS II, the heading and attitude valid lines have to be connected to the TPU67A Processor.  On valid state, the signals are +28VDC.  On invalid, the signals are open.  This condition of direct connection (without an isolation diode installed) of the valid lines to the TPU67A, if not corrected, could cause the TPU67A to feed current into the open stated valid lines.  This prevents the flag to appear even if the gyro is invalid, providing the flight crew with erroneous navigation information.

For the reasons stated above, this Directive requires the installation of isolation diodes into the signal lines to the TPU67A to prevent reverse feed of the valid lines.

Charles Lenarcic
Delegate of the Civil Aviation Safety Authority

16 March 2007