Document ID: chunk:federal_register_of_legislation:F2021L01225:body:0:p3
Version: federal_register_of_legislation:F2021L01225
Segment Type: other
Provision Reference: 
Character Range: 11607–13373

enable a digital link between the air data computer and the transponder.
               Note 5:  EASA AD 2009-0173R1 is the basis for this AD.
Compliance:    For Requirement 1 - Within 60 days after the commencement date of this AD, unless previously accomplished in accordance with a previous issue of this AD.
               For Requirement 2 - Concurrent with the accomplishment of the Requirement 1 modification of the aeroplane.
               For Requirement 3 - After the commencement date of this AD.
Commencement:  This AD commences on 10 September 2021.
Background:    The original issue of this Directive advised of a mismatch between the ARINC (formerly Aeronautical Radio Inc.) and General Aviation Manufacturers Association (GAMA) specifications for the Selected Altitude in Motion Bit of label 102 in certain Rockwell Collins TDR-94 transponders is causing incorrect transmission of the Mode-S Selected Altitude parameter.
               This condition, if not corrected, could lead to invalid Selected Altitude data being transmitted to Mode S ground stations, creating disruptions in the Air Traffic Management process and potentially compromising aeroplane safety.
               For the reasons described above, the original issue of this Directive required the modification or replacement of the affected transponders and prohibited reinstallation of unmodified units.
               Amendment 1 of this AD continued those requirements and at the same time supplied relief from those requirements for operators of some DHC-8 aircraft.
               Amendment 2 of this AD removes obsolete references and makes minor editorial changes to reflect current requirements.

David Punshon
Delegate of the Civil Aviation Safety Authority
27 August 2021