AD Number:AD/RAD/84 Honeywell RCZ-83 and RCZ-85 Communications Units 10/2005 TX
Applicability: Honeywell RCZ-83 and RCZ-85 Communication Units with Part Numbers (P/N) 7510700-725, -763, -765, -813, -815, -825, -863 and -875.
Note 1: These units are known to be fitted to, but not limited to, the following models:

• Embraer RJ 145
• Embraer RJ 135
• Falcon Jet 900
• British Aerospace HS 125-800
• British Aerospace HS 125-1000
• Hawker Series 125-800
• Hawker Series 125-1000
• Bombardier BD-700
• Cessna Citation CJ 1
• Cessna Citation CJ 2
• Cessna Citation 550
• Cessna Citation 560
• Cessna Citation 650
• Learjet 45
• Lockheed C130
• British Aerospace Jetstream 41
• Falcon Jet 2000
• Lockheed L382G

Requirement: 1. Amend the applicable Aircraft Flight Manual (AFM) by inserting the following statement into the Normal Procedures Section: "After completion of any 4096 ATC Code change (also referred to as Mode A Code), check the status of the transponder. If the transponder indicates that it is in standby mode, re-select the desired mode (i.e. the transponder should be in the active mode)." Amendment of the AFM Normal Procedures Section may be accomplished by inserting a copy of this Directive into the AFM

2. Modify the Communications Units by incorporating Honeywell Service Bulletin (SB) Publication No A21-3851-005 dated 29 July 2005 or Honeywell SB Publication No A24-3851-002 dated 28 July 2005 as applicable. Honeywell Technical Newsletter A23-1146-004 dated 9 December 2004 also refers.

3. Remove the AFM inserted in compliance with Requirement 1.

Note 2: EASA AD 2005-0021 refers. Compliance: For Requirement 1 - Within five days after the effective date of this Directive.

For Requirement 2 - Within nine calendar months after the effective date of this Directive. For Requirement 3 - Concurrent with compliance with Requirement 2.

This Airworthiness Directive becomes effective on 5 August 2005.

Background: The European Aviation Safety Agency (EASA) has advised of a design deficiency in RCZ-83 and RCZ-85 Communication Units manufactured by Honeywell which causes the associated transponder to revert to standby mode if a change of the 4096 ATC code (also referred to as the Mode A code) is not completed within 5 seconds. As a consequence, the Secondary Surveillance Radar (SSR) symbol and label associated with the aircraft's position will no longer be shown on the Air Traffic Control (ATC) ground radar display. Also, aircraft collision avoidance systems (ACAS) on board own and other aircraft will be compromised. Current operational procedures, typically, do not require the crew to recheck the transponder status after changing the 4096 ATC Code. This type of failure will increase ATC workload and will result in improper functioning of ACAS.

This Directive requires the insertion of an AFM amendment and the modification of the Control Unit.

FMI: www.casa.gov.au