Note.— Wherever the variable “level” is specified, the message can specify either a single level or a vertical range, i.e. block level.
Table A5-21. Emergency and urgent messages (downlink)
Message intent/use  Message element  URG  ALRT  RESP 
55  Urgency prefix.  PAN PAN PAN  U  H  Y 
56  Distress prefix.  MAYDAY MAYDAY MAYDAY  D  H  Y 
112  Indicates specifically that the aircraft is being subjected to unlawful interference.  SQUAWKING 7500  U  H  N 
57  Notification of fuel remaining and number of persons on board.  (remaining fuel) OF FUEL REMAINING AND (persons on board) PERSONS ON BOARD  U  H  Y 
58  Notification that the pilot wishes to cancel the emergency condition.  CANCEL EMERGENCY  U  M  Y 

Message intent/use  Message element  URG  ALRT  RESP 
59  Notification that the aircraft is diverting to the specified position via the specified route due to an urgent need.  DIVERTING TO (position) VIA (route clearance)  U  H  Y 
60  Notification that the aircraft is deviating the specified distance in the specified direction off the cleared route and maintaining a parallel track due to an urgent need.  OFFSETTING (specified distance) (direction) OF ROUTE  U  H  Y 
61  Notification that the aircraft is descending to the specified level due to an urgent need.  DESCENDING TO (level)  U  H  Y 
80  Notification that the aircraft is deviating up to the specified distance from the cleared route in the specified direction due to an urgent need.  DEVIATING UP TO (specified distance) (direction) OF ROUTE  U  H  Y 

Note.— Wherever the variable “level” is specified, the message can specify either a single level or a vertical range, i.e. block level.
Table A5-22. System management messages (downlink)
Message intent/use  Message element  URG  ALRT  RESP 
62  A system-generated message that the avionics has detected an error.  ERROR (error information)  U  L  N 
63  A system-generated denial to any CPDLC message sent from a ground facility that is not the current data authority.  NOT CURRENT DATA AUTHORITY  L  L  N 
99  A system-generated message to inform a ground facility that it is now the current data authority.  CURRENT DATA AUTHORITY  L  L  N 
64  Notification to the ground system that the specified ATSU is the current data authority.  (facility designation)  L  L  N 
107  A system-generated message sent to a ground system that tries to connect to an aircraft when a current data authority has not designated the ground system as the NDA.  NOT AUTHORIZED NEXT DATA AUTHORITY  L  L  N 
73  A system-generated message indicating the software version number.  (version number)  L  L  N 

No. 2

Message intent/use  Message element  URG  ALRT  RESP 
100  Confirmation to the ground system that the aircraft system has received the message to which the logical acknowledgement refers and found it acceptable for display to the responsible person.  LOGICAL ACKNOWLEDGEMENT  N  M  N 

Table A5-23. Additional messages (downlink)
Message intent/use  Message element  URG  ALRT  RESP 
65  Used to explain reasons for pilot’s message.  DUE TO WEATHER  L  L  N 
66  Used to explain reasons for pilot’s message.  DUE TO AIRCRAFT PERFORMANCE  L  L  N 
　
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