Document ID: chunk:federal_register_of_legislation:F2009L01504:body:0:p2
Version: federal_register_of_legislation:F2009L01504
Segment Type: other
Provision Reference: 
Character Range: 5448–7318

communication.  One type of 'PLOC' occurrence can be caused by equipment not receiving radio communication from an Air Traffic Controller or another aircraft.  Typically, this type of failure is temporary and can be corrected by the crew of the aircraft transmitting a radio message.  Following this transmission, the equipment correctly receives all incoming radio signals.  This type of failure is referred to a 'sleeping receiver' problem.

             This type of problem causes workload issues for the Air Traffic Controller and can result in a reduction in safety levels.  It is important, therefore, to do all that is possible to reduce or eliminate this type of occurrence.

             Thales, during exhaustive testing, managed to re-create the problem of the 'sleeping receiver' once.  Further testing failed to induce the failure and the actual cause of the problem still remains unknown.

             Thales, however, instigated a design change to eliminate the possibility of this type of occurrence by checking every 20ms, when not transmitting, that the "sleeping receiver" conditions are not fulfilled and by forcing it into receive mode if it is not the case.  The modified Thales VHF data radio is now installed on some aircraft.  Since installing the modified radio, no reports of any 'PLOC' occurrences attributable to a 'sleeping receiver' have been received.

             For this reason, it is considered that the modification as per the Thales Service Bulletins should be mandatory for all aircraft with these models of radio installed.
             This Amendment corrects some minor omissions from the original issue of the Directive and extends compliance by 12 months.

   The original issue of this Directive became effective on 15 February 2007.

James Coyne
Delegate of the Civil Aviation Safety Authority

26 March 2009