This is a proposed spec only

Airport Tiles

Airport tiles are the graphical component of the airport. They have no direct interaction or effect on the state machine on or aircraft.

Action 0 Airport Tiles

Land shape flags
Animation information
Animation speed

as per Properties for industry tiles 0D, 0F and 10

Tile Subname string (ie, clicking ? on this tile will give you "AirportName (TileSubname)")

Action 2 Airport Tiles

as per Action 2 for houses and industry tiles

Var Action 2 Airport Tiles

as per Variational Action 2 Variables for Industry Tiles, except of course "industry" -> "airport".

Callbacks for Airport Tiles

Next animation frame (1A/26/141)
Animation control (1B/25/140)
Custom shape check (2F)
Decide drawing default foundations (30)
Disable autosloping for industry tiles (3C)

Airports

Airports are the logical component of the airport. The airport contains the state machine.

Action 0 Airports

Name
Class
Small/Large/Helipad/Oilrig (note: for backwards compatibility with vehicle var 44)
Years available
Catchment area
Noise level
Text string to show in the build list
Cost per new tile when building
Cost per overbuilt tile when building
Yearly facility maintanance cost (possibly ?)

Tile array similar to Industry Property 0A
Node array. Each node has an x,y,z position, and a flag byte (hangar, contact point, loading bay) used for overbuilding, buying/selling aircraft in the hangar and, in the case of the contact point(s), aircraft interception from outside the state machine.

Action 2 Airports

The icon to show in the build list.

Var Action 2 Airports

Year built
Days since an aircraft last arrived or was loading at any node
Days since an aircraft last arrived or was loading at a specific node (60+)
Quantity of passengers waiting at the airport
Quantity of mail waiting at the airport
Quantity and ID of most common other cargo waiting at the airport
Variable 7C, 16 4-byte slots of persistent data

Callbacks for Airports

statemachine callback

The statemachine callback is called when an aircraft wants to leave a node. The 3rd nibble contains the following flags:

0 = fly/taxi to the node specified in the low byte
1 = change the movement state to the value specified in the low byte and reiterate
2 = turn to the heading specified in the low byte and wait for 16 ticks before reiterating
8 = begin loading/unloading
A = play the sound effect specified in the low byte and reiterate
C = throw the alert message specified in the low byte, change plan to "heading for a hangar" and reiterate
D = throw the alert message specified in the low byte, change plan to "heading for an exit" and reiterate
E = throw the alert message specified in the low byte and stop the aircraft (if it's on the ground) or leave the statemachine and move to the next order (if it's in the air)
F = leave the statemachine and move to the next order

(note: throwing an alert and stopping the aircraft is probably not a good idea unless the aircraft is in a hangar!)

Var 10 contains the number of the node that was triggered. Var 11 contains information on the aircraft's current plan:

0 = heading for a bay
1 = heading for a hangar
2 = heading for an exit
80 = this is a reiteration after waiting

Type 82 within the callback gets the variables of the aircraft which triggered the callback. This callback + Variable 7C completely replaces the hardcoded state machine!!

Aircraft

Aircraft gain Variable 7C, and an additional property to provide information to the airport state machine.

Action 0 Aircraft

2B = basic aircraft information.

01-0F = runway length required
10 = large aircraft
20 = seaplane (only)
40 = amphibious
80 = special aircraft (airport may want to send it to a special bay/apron).

This property goes into 'uu' in Vehicle Variable 42.

Miscellaneous information

An aircraft heading for an airport will always head for the closest contact point node.

Overbuilding

Airports can be overbuilt like stations, even if aircraft are currently on the airport. Building a new airport tile over an existing airport tile can have a different cost from building one on empty ground (see airport action 0s above). When an airport is overbuilt, the airport's persistent data variables are reset, and the following happens to the aircraft on the airport:

All aircraft currently loading will have their plan changed to "heading for a bay", will be placed randomly at the loading bay nodes of the new airport, and will run the state machine callback to lock themselves in to the bay. Loading aircraft that don't fit will be moved to the first defined hangar.
All other aircraft on the ground will be moved to the airport's first defined hangar.
All aircraft in the air will move to the first defined contact point.

If the airport wants to move aircraft to a hangar but doesn't have one, the overbuilding will fail.

Example Airports

To follow. ;)

Newgrf Airports Documentation

Contents