Downlink

A message sent from an aircraft to an ATSU is known as an downlink. Depending on the response attribute of a given message, an ATSU may or may not have to respond with one of the allowed uplink messages.

Response Attributes

Resp.	Description
Y	Response Required with any uplink message
N	Response Not Required, and the message should be considered closed even though a response may be uplinked by the ATSU The GOLD specification accomodates logical acknowledgements. Not sure if we want these.

List of Messages

If a position report message type is desirable, we would need to work out which fields are necessary. I am unable to confirm the exact fields that are included in real-world position reports, but the following is likely needed at a minimum:

ID	Resp.	Formatted Message
`DM48`	N	`POSITION REPORT [time] [position] [altitude] [speed]`

Aircraft-specific documentation implies the presence of data on winds aloft, course offset, estimated time of arrival, and temperature. I would like to be able to corroborate this with other sources.

ID	Resp.	Formatted Message
`DM0`	N	`WILCO`
`DM1`	N	`UNABLE`
`DM2`	N	`STANDBY`
`DM3`	N	`ROGER`
`DM4`	N	`AFFIRM`
`DM5`	N	`NEGATIVE`

`DM6`	Y	`REQUEST [altitude]`
`DM7`	Y	`REQUEST BLOCK [altitude] TO [altitude]`
`DM9`	Y	`REQUEST CLIMB TO [altitude]`
`DM10`	Y	`REQUEST DESCENT TO [altitude]`
`DM11`	Y	`AT [position] REQUEST CLIENT TO [altitude]`
`DM12`	Y	`AT [position] REQUEST DESCENT TO [altitude]`
`DM13`	Y	`AT TIME [time] REQUEST CLIMB TO [altitude]`
`DM14`	Y	`AT TIME [time] REQUEST DESCENT TO [altitude]`
`DM15`	Y	`REQUEST OFFSET [distance] [direction] OF ROUTE`
`DM18`	Y	`REQUEST [speed]`
`DM20`	Y	`REQUEST VOICE CONTACT`
`DM22`	Y	`REQUEST DIRECT TO [position]`
`DM23`	Y	`REQUEST [procedure]`
`DM24`	Y	`REQUEST [route clearance]`
`DM25`	Y	`REQUEST CLEARANCE`
`DM27`	Y	`REQUEST WEATHER DEVIATION UP TO [distance] [direction] OF ROUTE`
`DM34`	N	`PRESENT SPEED [speed]`
`DM38`	N	`ASSIGNED ALTITUDE [altitude]`
`DM40`	N	`ASSIGNED ROUTE [route clearance]`
`DM41`	N	`BACK ON ROUTE`
`DM55`	N	`PAN PAN PAN`
`DM56`	N	`MAYDAY MAYDAY MAYDAY`
`DM57`	N	`[time] OF FUEL REMAINING AND [number] ON BOARD`
`DM58`	N	`CANCEL EMERGENCY`
`DM59`	N	`DIVERTING TO [position] VIA [route clearance]`
`DM60`	N	`OFFSETTING [distance] [direction] OF ROUTE`
`DM61`	N	`DESCENDING TO [altitude]`
`DM62`	N	`ERROR [text]`
`DM63`	N	`NOT CURRENT DATA AUTHORITY`
`DM65`	N	`DUE TO WEATHER`
`DM66`	N	`DUE TO AIRCRAFT PERFORMANCE`
`DM77`	N	`ASSIGNED BLOCK [altitude] TO [altitude]`
`DM80`	N	`DEVIATING [distance] [direction] OF ROUTE`
`DM99`	N	`CURRENT DATA AUTHORITY`
`DM107`	N	`NOT AUTHORIZED NEXT DATA AUTHORITY`

`DM67`	N	`[text]`
`DM68`	Y	`[text]`