Note.— Wherever the variable “level” is specified, the message can specify either a single level or a vertical range, i.e. block level.
Table A5-3. Crossing constraints (uplink)
Message intent/use  Message element  URG  ALRT  RESP 
42  Notification that a level change instruction should be expected which will require the specified position to be crossed at the specified level.  EXPECT TO CROSS (position) AT (level)  L  L  R 
43  Notification that a level change instruction should be expected which will require the specified position to be crossed at or above the specified level.  EXPECT TO CROSS (position) AT OR ABOVE (level)  L  L  R 
44  Notification that a level change instruction should be expected which will require the specified position to be crossed at or below the specified level.  EXPECT TO CROSS (position) AT OR BELOW (level)  L  L  R 
45  Notification that a level change instruction should be expected which will require the specified position to be crossed at the specified level which is to be maintained subsequently.  EXPECT TO CROSS (position) AT AND MAINTAIN (level)  L  L  R 
46  Instruction that the specified position is to be crossed at the specified level. This may require the aircraft to modify its climb or descent profile.  CROSS (position) AT (level)  N  M  W/U 
47  Instruction that the specified position is to be crossed at or above the specified level.  CROSS (position) AT OR ABOVE (level)  N  M  W/U 
48  Instruction that the specified position is to be crossed at or below the specified level.  CROSS (position) AT OR BELOW (level)  N  M  W/U 
49  Instruction that the specified position is to be crossed at the specified level and that level is to be maintained when reached.  CROSS (position) AT AND MAINTAIN (level)  N  M  W/U 
50  Instruction that the specified position is to be crossed at a level between the specified levels.  CROSS (position) BETWEEN (level) AND (level)  N  M  W/U 

No. 2

Message intent/use  Message element  URG  ALRT  RESP 
51  Instruction that the specified position is to be crossed at the specified time.  CROSS (position) AT (time)  N  M  W/U 
52  Instruction that the specified position is to be crossed at or before the specified time.  CROSS (position) AT OR BEFORE (time)  N  M  W/U 
53  Instruction that the specified position is to be crossed at or after the specified time.  CROSS (position) AT OR AFTER (time)  N  M  W/U 
54  Instruction that the specified position is to be crossed at a time between the specified times.  CROSS (position) BETWEEN (time) AND (time)  N  M  W/U 
55  Instruction that the specified position is to be crossed at the specified speed and the specified speed is to be maintained until further advised.  CROSS (position) AT (speed)  N  M  W/U 
56  Instruction that the specified position is to be crossed at a speed equal to or less than the specified speed and the specified speed or less is to be maintained until further advised.  CROSS (position) AT OR LESS THAN (speed)  N  M  W/U 
57  Instruction that the specified position is to be crossed at a speed equal to or greater than the specified speed and the specified speed or greater is to be maintained until further advised.  CROSS (position) AT OR GREATER THAN (speed)  N  M  W/U 
58  Instruction that the specified position is to be crossed at the specified time and at the specified level.  CROSS (position) AT (time) AT (level)  N  M  W/U 
　
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