Tower — Play Free in Your Browser

What Is Tower?

Tower is a radar scope, one runway, and a stream of aeroplanes that will not stop coming. Each blip arrives at the edge of the screen with a heading and a level already set, flies straight until somebody speaks to it, and the somebody is you. Aircraft turn up roughly every 1.9 seconds.

You have three instructions to give: a heading, dragged out from the aircraft itself; a level, chosen from the nine rungs on the ladder down the right-hand side, running from the ground to 8,000 feet in thousand-foot steps; and a clearance, which sends an aircraft down to land. Your score is landings. The meter beside it starts at 100 and only ever falls, and at zero the airspace closes and the shift is over.

Reading the Scope

Four things you can do to an aircraft, and they are not interchangeable.

A heading: Drag from the aircraft and its nose swings onto the line you drew at 1.8 radians a second. Fast enough to matter, slow enough that a turn made late arrives late. Point an aircraft away from the field and it stops being an arrival and becomes a problem for later.
A level: Click a rung on the ladder, or press the up and down arrows, and the aircraft moves in thousand-foot steps. Two of them may sit as close together as you like provided they are 1,000 feet apart vertically, which makes height the only instruction that buys separation without spending distance.
A clearance: The one that scores. A cleared aircraft turns for the field, descends at 2,600 feet a second, and touches down as soon as it is over the runway below 600 feet. Give it any other instruction afterwards and the approach is cancelled.
Doing nothing: Six seconds after you last touched an aircraft, the tower’s fallback automation takes it and flies it at the runway. The landing counts. It is also flown with no idea where anybody else is.

How to Play

Open the tower and aircraft begin arriving almost at once, one every 1.9 seconds or so, with the gaps narrowing as the shift wears on.
Click a blip to take it. Brackets appear around it, and a tag in the bottom left corner gives its callsign, its heading and its level.
Drag anywhere on the scope to vector it. The dashed line is the heading you are asking for, and the aircraft turns onto it and holds it until you say something else.
Assign a level by clicking a rung on the ladder or pressing the arrow keys. Aircraft climb and descend at 1,400 feet a second, which is quick, and the ladder reaches from the ground to 8,000 feet.
Separate in height before you separate in distance. Two aircraft converging on the same patch of sky are cheapest to fix by putting one of them a thousand feet above the other.
Clear an aircraft to land with a click on the runway or the L key, and do it when nothing else is on the same piece of the approach. An arrival flown onto an occupied runway goes around instead.

The runway blocks for one second after each touchdown, so it is almost never the runway that limits you. It is the final approach, and how many aircraft you have allowed onto it at once.

What the Tower Does When You Look Away

Leave an aircraft alone for six seconds and the automation takes it, sets its level to zero and points its nose at the field. The landing that follows is real and it lands on your score. Hands off, with no controller at all, that is what happens to nearly everything on the scope.

What the automation cannot do is see the rest of the board. It has no idea that somebody is already on final, or that the aircraft it just turned will cut across the runway at the worst possible moment. Each aeroplane is flown perfectly and the airspace as a whole is flown badly, and the bill arrives as a conflict or a go-around.

Altitude Is the Only Cheap Tool

The separation minimum is 34 pixels across and 1,000 feet vertically, and both halves have to fail before the meter is charged. So the same crowded patch of sky can hold two aircraft perfectly legally as long as one of them is a thousand feet higher. Moving somebody in height costs you the height. Moving them sideways costs you their track and their arrival time.

The ladder gives you nine levels. Arrivals show up between 3,000 and 8,000 feet, so the top six rungs are busy the moment they appear and the bottom three are yours to build shelves in.

Why Go-Arounds Compound

An aircraft that reaches a runway still blocked from the last touchdown does not wait for it. It goes around, which costs 4 per cent of the meter, and it pays that price in the worst place available: low, close to the field, and pointed away from it.

Then its clock restarts, and six seconds later the automation flies it at the same runway from a worse position, in company with everything that has arrived since. That is how one late arrival becomes a queue.

What the Meter Is Charging You For

The drain opens at 1.4 per cent a second and gains another 0.045 every second it runs, so it is always accelerating. A landing hands back 1 per cent. A loss of separation costs 2.5 the moment it starts and 5 for every second the pair stay inside the minimum. A go-around is 4, and letting an aircraft wander off the scope is 3.

The arithmetic explains the shape of a shift. Landings cannot cover the drain, and late on they barely slow it down. What you are protecting is the meter you have not spent yet, and the two things that spend it fastest are conflicts and go-arounds.

Tower on a Phone

The scope is scaled to the height of the screen rather than to a fixed pixel size, so the separation minimum covers the same fraction of the picture on a phone as it does on a desktop, and a shift played with a thumb is the same shift.

Everything works by touch. Tap a blip to take it, drag on the scope to steer it, tap a rung to change its level. The ladder sits on the right edge where a thumb already is, and the tag for the selected aircraft sits in the bottom left, clear of everything you have to reach.

Questions

Tower — FAQ

Why did the shift end when nothing had gone wrong?

Because the meter falls on its own. The base drain starts at 1.4 per cent a second and gains another 0.045 every second, and it runs whether you touch anything or not. Landings give a little back, never as much as the shift takes, so the only question is how long you can make it last.

Why did an aircraft I had cleared suddenly turn away?

Because you gave it a second instruction. Any heading or level change cancels an approach, since the automation will not fly a level and a landing at the same time. The tag reads CLEARED TO LAND right up until you break it off.

Why did the tower land something I was about to deal with?

You had not spoken to it for six seconds, so the fallback took it. The bar in its tag drains as that clock runs and it is the only warning you get. Touching an aircraft resets the clock, even if all you do is change its level.

Two aircraft were miles apart and still cost me. How?

Separation is measured in two directions at once: 34 pixels across and 1,000 feet vertically, with both needed before the meter is charged. A pair on opposite sides of the scope is free. A pair at the same level in the same place costs 5 per cent a second.

How do I get more landings out of a shift?

Keep the final approach empty rather than the runway itself. The runway only blocks for a second, so your real constraint is how many aircraft you let onto the approach at once. Stagger them in time, and hold the ones that would otherwise arrive together.

What is the most expensive mistake I can make?

Letting one drift off the edge of the scope, at 3 per cent. A conflict is dearer if you leave it running, at 5 per cent a second on top of a 2.5 per cent entry charge, but a conflict is something you can still fix. An aircraft off the scope is gone and you paid for the privilege.

Is it ever right to let an aircraft go around?

Often, yes. A go-around costs 4 per cent and gives you an aircraft six seconds later from a worse position, which sounds like a bad trade and frequently is. But sending one into a runway that is still blocked costs more, and the meter charges you either way.

Keep flying