Airport Collaborative Decision Making (A-CDM) Controller Guide¶
What is A-CDM?¶
On VATSIM, A-CDM is a tool that encourages virtual pilots, controllers, and dispatchers to coordinate more effectively - much like in the real world, but adapted for an online flight simulation environment. By sharing essential departure data, planning collaborative push-back times, and adhering to consistent procedures, A-CDM helps to reduce airfield congestion and improve overall traffic flow. The result is a more immersive, realistic, and seamless experience for everyone involved in the virtual aviation community. It links with the ECFMP and event slots to ensure that pilots who have event slots depart on time, and controls departure rates to prevent overloading of runway holding points, enroute sectors and arrival airfields. The below instructions describe how ADC controllers in VATSIM UK should use A-CDM to ensure an efficient traffic flow during busy events.
Note
A-CDM can be used by controllers at any time they deem necessary. At certain events, the use of A-CDM will be notified as mandatory. As a general rule of thumb, if opening a GMP position at a busy airfield, it is advised to enable the system.
Timings¶
There are many significant points in the lead up to an aircraft departing an airfield. These significant points are labelled using different acronyms. Below are the most pertinent for use on the VATSIM network.
| Time | Description |
|---|---|
| EOBT | The departure time entered by the pilot on the flightplan, not useful for VATSIM as this is normally inaccurate |
| TOBT | When the aircraft aims to push back |
| TSAT | When ATC plans to approve start, considering flow restrictions, taxi times, capacity etc. |
| TTOT | When the A-CDM system estimates the aircraft will be airborne. |
| CTOT | Also known as a "slot". The aircraft must depart -5/+10 minutes of this time. |
Enabling The Plugin¶
The plugin is already configured in the UK Controller Pack for all SMR profiles. List items have similarly been set up to provide a balance between showing the most pertinent times, but omitting times that are not commonly useful to controllers on the VATSIM network.
Each airfield must have a "master", with other controllers at the same airfield acting as slave. Normally, the controller providing the GMP function will be the "master".
.cdm master {airport} will enable you as the master for the airfield
.cdm slave {airport} will enable you to receive CDM data for the airfield
Controller Handover¶
During a controller handover, the existing master will use the command .cdm slave {airport}, followed by the incoming controller using .cdm master {airport}.
A-CDM Colours¶
TOBT¶
| Colour | Defintion |
|---|---|
 LIGHT GREEN |
Before TOBT -5 |
 DARK GREEN |
TOBT -5 -> -2 |
 YELLOW |
Last minute of TOBT |
TSAT¶
| Colour | Defintion |
|---|---|
LIGHT GREEN |
TOBT -35 to TSAT -5 |
DARK GREEN |
TSAT -5 to TSAT +5 |
YELLOW |
From TSAT +5 to TSAT +6 |
 RED |
TSAT >+6 (Expired) |
CTOT¶
| Colour | Defintion |
|---|---|
GREEN |
CDM Server CTOT |
 ORANGE |
Manual/Event CTOT |
RED |
Flow/CAD CTOT |
Controller responsibilities¶
GMP / Planner¶
Slotted Events¶
Events with CTOTs will be added to the system prior to the event. This is linked to the pilots' CID.
When a pilot logs in, the system will automatically show the event CTOT in the EVNT column. To add the Event CTOT to the A-CDM system, the GMP controller must left click on the event CTOT. This will then generate the A-CDM times.
When the pilot calls for clearance, GMP shall advise the aircraft of the TSAT.
Radiotelephony
BIGJET123, cleared to Kennedy, CPT3G departure, Squawk 1234, QNH 1013. Expect start at time 1200.
Once within TSAT +/-5 minutes (colour is dark green), the aircraft can be passed to GMC for start up.
Pilots without a slot or those who miss their TSAT by more than 5 minutes should be treated as below.
Non-slotted/Overload Events¶
When the aircraft calls ready for start, GMP will left click the TOBT to generate the A-CDM system times. If the TSAT is within +/-5 minutes (dark green), the aircraft can be passed to GMC for start up.
If the TSAT is not within +/- 5 minutes (light green), advise the aircraft of the TSAT and advise them to hold position.
GMC¶
Once an aircraft calls fully ready, the GMC controller must check the TSAT is within the +/- 5 minute window. If it is, start up can be issued.
The TTOT/CTOT columns in the taxi out list can be used to determine a reasonable order to taxi the aircraft to the holding point in. However, final sequencing for departure remains with the AIR controller.
AIR¶
The AIR controller shall use the TTOT/CTOT fields alongside applying the normal route/speed/wake separation to determine the departure order. Where a CTOT is given, this should be prioritised to ensure flow restrictions such as MDIs are adhered to.