Uplink
A message sent from an ATSU to an aircraft is known as an uplink. Depending on the response attribute of a given message, an aircraft may or may not have to respond with one of the allowed downlink messages.
Response Attributes
Section titled “Response Attributes”| Resp. | Description |
|---|---|
| W/U | Response Required with one of the following downlink messages:
|
| A/N | Response Required with one of the following downlink messages:
|
| R | Response Required with one of the following downlink messages:
|
| Y | Response Required with any downlink message |
| N | Response Not Required, but one of the following downlink messages could be sent:
|
| NE | Response Not Required, and the message should be considered closed even though a response may be downlinked by the aircraft |
List of Messages
Section titled “List of Messages”| ID | Resp. | Formatted Message |
|---|---|---|
| UM0 | N | UNABLE |
| UM1 | N | STANDBY |
| UM3 | N | ROGER |
| UM4 | N | AFFIRM |
| UM5 | N | NEGATIVE |
| UM19 | W/U | MAINTAIN [altitude] |
| UM20 | W/U | CLIMB TO [altitude] |
| UM23 | W/U | DESCEND TO [altitude] |
| UM26 | W/U | CLIMB TO REACH [altitude] BY [time] |
| UM27 | W/U | CLIMB TO REACH [altitude] BY [position] |
| UM28 | W/U | DESCEND TO REACH [altitude] BY [time] |
| UM29 | W/U | DESCEND TO REACH [altitude] BY [position] |
| UM30 | W/U | MAINTAIN BLOCK [altitude] TO [altitude] |
| UM31 | W/U | CLIMB TO AND MAINTAIN BLOCK [altitude] TO [altitude] |
| UM32 | W/U | DESCEND TO AND MAINTAIN BLOCK [altitude] TO [altitude] |
| UM36 | W/U | EXPEDITE CLIMB TO [altitude] |
| UM37 | W/U | EXPEDITE DESCENT TO [altitude] |
| UM38 | W/U | IMMEDIATELY CLIMB TO [altitude] |
| UM39 | W/U | IMMEDIATELY DESCEND TO [altitude] |
| UM46 | W/U | CROSS [position] AT [altitude] |
| UM47 | W/U | CROSS [position] AT OR ABOVE [altitude] |
| UM48 | W/U | CROSS [position] AT OR BELOW [altitude] |
| UM49 | W/U | CROSS [position] AT AND MAINTAIN [altitude] |
| UM51 | W/U | CROSS [position] AT [time] |
| UM52 | W/U | CROSS [position] AT OR BEFORE [time] |
| UM53 | W/U | CROSS [position] AT OR AFTER [time] |
| UM54 | W/U | CROSS [position] BETWEEN [time] AND [time] |
| UM55 | W/U | CROSS [position] AT [speed] |
| UM56 | W/U | CROSS [position] AT OR LESS THAN [speed] |
| UM57 | W/U | CROSS [position] AT OR GREATER THAN [speed] |
| UM61 | W/U | CROSS [position] AT [altitude] AT [speed] |
| UM64 | W/U | OFFSET [distance] [direction] OF ROUTE |
| UM72 | W/U | RESUME OWN NAVIGATION |
| UM74 | W/U | PROCEED DIRECT TO [position] |
| UM75 | W/U | WHEN ABLE PROCEED DIRECT TO [position] |
| UM76 | W/U | AT [time] PROCEED DIRECT TO [position] |
| UM77 | W/U | AT [position] PROCEED DIRECT TO [position] |
| UM78 | W/U | AT [altitude] PROCEED DIRECT TO [position] |
| UM79 | W/U | CLEARED TO [position] VIA [route clearance] |
| UM80 | W/U | CLEARED [route clearance] |
| UM81 | W/U | CLEARED [procedure] |
| UM82 | W/U | CLEARED TO DEVIATE UP TO [distance] [direction] OF ROUTE |
| UM83 | W/U | AT [position] CLEARED [route clearance] |
| UM84 | W/U | AT [position] CLEARED [procedure] |
| UM91 | W/U | HOLD AT [position] MAINTAIN [altitude] INBOUND TRACK [degrees] [direction] TURN LEG TIME [leg type] |
| UM92 | W/U | HOLD AT [position] AS PUBLISHED MAINTAIN [altitude] |
| UM93 | R | EXPECT FURTHER CLEARANCE AT [time] |
| UM94 | W/U | TURN [direction] HEADING [degrees] |
| UM96 | W/U | CONTINUE PRESENT HEADING |
| UM106 | W/U | MAINTAIN [speed] |
| UM107 | W/U | MAINTAIN PRESENT SPEED |
| UM108 | W/U | MAINTAIN [speed] OR GREATER |
| UM109 | W/U | MAINTAIN [speed] OR LESS |
| UM116 | W/U | RESUME NORMAL SPEED |
| UM117 | W/U | CONTACT [unit name] [frequency] |
| UM120 | W/U | MONITOR [unit name] [frequency] |
| UM123 | W/U | SQUAWK [beacon code] |
| UM127 | R | REPORT BACK ON ROUTE |
| UM134 | NE | CONFIRM SPEED |
| UM135 | NE | CONFIRM ASSIGNED ALTITUDE |
| UM137 | NE | CONFIRM ASSIGNED ROUTE |
| UM148 | NE | WHEN CAN YOU ACCEPT [altitude] |
| UM153 | R | ALTIMETER [altimeter] |
| UM154 | R | RADAR SERVICES TERMINATED |
| UM157 | R | CHECK STUCK MICROPHONE [frequency] |
| UM159 | N | ERROR [error information] |
| UM160 | N | NEXT DATA AUTHORITY [facility ident] |
| UM161 | N | END SERVICE |
| UM163 | N | [atsu unit] |
| UM166 | N | DUE TO TRAFFIC |
| UM167 | N | DUE TO AIRSPACE RESTRICTION |
| UM179 | W/U | SQUAWK IDENT |
| UM183 | N | CURRENT ATC UNIT [unit name] |
| UM169 | R | [text] |