Table A5-17. Voice contact requests (downlink)
Message intent/use  Message element  URG  ALRT  RESP 
20  Request for voice contact.  REQUEST VOICE CONTACT  N  L  Y 
21  Request for voice contact on the specified frequency.  REQUEST VOICE CONTACT (frequency)  N  L  Y 

Table A5-18. Route modification requests (downlink)
Message intent/use  Message element  URG  ALRT  RESP 
22  Request to track from the present position direct to the specified position.  REQUEST DIRECT TO (position)  N  L  Y 
23  Request for the specified procedure clearance.  REQUEST (procedure name)  N  L  Y 
24  Request for a route clearance.  REQUEST CLEARANCE (route clearance)  N  L  Y 

No. 2

Message intent/use  Message element  URG  ALRT  RESP 
25  Request for a clearance.  REQUEST (clearance type) CLEARANCE  N  L  Y 
26  Request for a weather deviation to the specified position via the specified route.  REQUEST WEATHER DEVIATION TO (position) VIA (route clearance)  N  M  Y 
27  Request for a weather deviation up to the specified distance off track in the specified direction.  REQUEST WEATHER DEVIATION UP TO (specified distance) (direction) OF ROUTE  N  M  Y 
70  Request a clearance to adopt the specified heading.  REQUEST HEADING (degrees)  N  L  Y 
71  Request a clearance to adopt the specified ground track.  REQUEST GROUND TRACK (degrees)  N  L  Y 

Table A5-19. Reports (downlink)
Message intent/use  Message element  URG  ALRT  RESP 
28  Notification of leaving the specified level.  LEAVING (level)  N  L  N 
29  Notification of climbing to the specified level.  CLIMBING TO (level)  N  L  N 
30  Notification of descending to the specified level.  DESCENDING TO (level)  N  L  N 
31  Notification of passing the specified position.  PASSING (position)  N  L  N 
78  Notification that at the specified time the aircraft’s position was as specified.  AT (time) (distance) (to/from) (position)  N  L  N 
32  Notification of the present level.  PRESENT LEVEL (level)  N  L  N 
33  Notification of the present position.  PRESENT POSITION (position)  N  L  N 
34  Notification of the present speed.  PRESENT SPEED (speed)  N  L  N 
113  Notification of the requested speed.  (speed type) (speed type) (speed type) SPEED (speed)  N  L  N 
35  Notification of the present heading in degrees.  PRESENT HEADING (degrees)  N  L  N 
36  Notification of the present ground track in degrees.  PRESENT GROUND TRACK (degrees)  N  L  N 
37  Notification that the aircraft is maintaining the specified level.  MAINTAINING (level)  N  L  N 
72  Notification that the aircraft has reached the specified level.  REACHING (level)  N  L  N 
76  Notification that the aircraft has reached a level within the specified vertical range.  REACHING BLOCK (level) TO (level)  N  L  N 

Message intent/use  Message element  URG  ALRT  RESP 
38  Read-back of the assigned level.  ASSIGNED LEVEL (level)  N  M  N 
77  Read-back of the assigned vertical range.  ASSIGNED BLOCK (level) TO (level)  N  M  N 
　
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