Q: What is this?
A: This is a Javascript remake of an ancient BSD game by Ed James called ATC (Air Traffic Control). The goal of the game is to guide as many airplanes safely to their destination as possible. The game ends when any two planes collide, any plane crashes, or illegaly exits the game arena.

Q: What are the difference between this remake and the original?
A: This remake follows the original gameplay very closely, with some liberties taken to enhance the interface. The graphics is intentionally simplistic, so that the game emulates an actual radar display. The greatest change is the removal of the destination table - now each plane has its destination displayed next to its name and altitude. The controls are mostly the same, except that some commands were not implemented because of my laziness ^^

Q: How do i play it?
A: As the air traffic controller, your task is to bring as many planes as possible to their destinations, while avoiding collisions and other dangers. A collision occurs when any two planes get into neighbouring squares,  and their respective altitudes are less than 2000 ft. apart. You will also lose if any plane leaves the board illegaly, exits through a wrong exit, lands at the wrong airport, or runs out of gas.
Each plane has its information displayed next to its icon. The first character is the plane's name, lower-case means that the plane is a jet (and moves twice as fast as an upper-case [propeller] plane). The plane's altitude is the second character times 1000 ft. In the parentheses is the plane's destination. (E - an exit, A - an airport)
All planes enter and leave the board through exits or airports. Planes entering your area will arrive with altitude of 7000 ft., while leaving planes must be at 9000 ft. To land a plane, set its altitude to 0 just as it moves over an airport. Take care to land in the proper direction, as marked on the airport's icon.

The game is controlled by keyboard alone. In order to guide a plane, first type a letter corresponding to its name. (Planes are named by single letters, A-Z. Lower-case planes are jets and they move twice as fast as the others.) The next entered letter describes the command:
A - set new altitude
    (0-9)
T - turn to heading:
    Q - 315 (NW)
    W - 0 (N)
    E - 45 (NE)
    A - 270 (W)
    D - 90 (E)
    Z - 225 (SW)
    X - 180 (S)
    C - 135 (SE)
I - Ignore (the plane will appear darker on your screen, it's used to declutter the display)
U - Unmark (just like Ignore, but the plane will light up again after it executes a becaon command)
M - Mark (cancels Ignore and Unmark)
C - fly in circles
Radio beacons are used to delay commands - you can order a plane to perform certain manuevers when they reach a specified beacon
Some commands can be delayed by typing AB<X>, which translates to "at beacon <X>".
All commands are confirmed with Enter.
Examples:
aa9 <enter> - Plane A, change altitude to 9000 ft.
ztx <enter> - Plane Z, Turn to 180.
a t d a b 0 <enter> Plane A, turn to 90 at beacon #0

UPDATE: 2013-12-20:

New features:

• New maps: airports, Atlantis, box. Current map can be changed by clicking links on the top of the screen.
• Planes can now be told circle at an airport (i.e. acaa2 means "A, circle at airport 2.")
• Tweaked the plane-spawning algorithm to make the game slightly more fair.

Bugfixes:

• Fixed random collisions caused by two planes spawning on top of each other.
• Prevented the browser from quitting the game when backspace was pressed (works in Firefox)
• Fixed the bug that caused the prop planes to move out of sync with each other.
• Increased the amount of fuel carried by planes; it now depends on the size of the map too.
• Low fuel warning now appears at 15 turns before crash (30 turns for prop planes)
• Fixed airport icons appearing at wrong positions.