Development Log

Every rule was read again and asked whether it was sane, simple and justified. Service becomes one company-wide setting, from no frills to full service, its cost growing with the hours an aircraft flies and the crew it carries. A refit is a purchase like any other and needs the cash; an aircraft on offer may still be refitted, its buyer taking it as it stands. A company below zero pays no other company — neither rent nor dividends — and a tie at the top of a share register leaves a company controlling itself, keeping its owner. A company's head office grows with its own aircraft and with each company it holds shares in, never with what those companies do.

A hub adds travellers to its own city without taking any from markets elsewhere. Every decision travels with the rest of its sitting, every line of the activity feed stays a real week, keeping the names and the outcome it showed, a request to join holds its username while it waits, and every screen reads the world the same way, so one page always agrees with the next. Every preview plays the coming day as it will happen, and nothing the phone already knows would fail can be confirmed.

A flight is its route, its days, a departure time, the minutes it stands at each stop — an hour to start, moved in quarter hours, never below what its type needs — and the type of aircraft it wants, or none yet; an airline that fits one type two ways may name the fit too. At each day boundary the game puts an aircraft of that type on every flight, the oldest flights first, each keeping the one it had where it can, and reads its seats, cabins and costs from that aircraft. A flight it cannot fly, or that finds no free aircraft or no gate at a stop, waits as a draft, and says why — at which airport, and on which days.

Picking a type that needs longer at a stop lengthens the stops that were shorter, and never shortens one. When an aircraft leaves the airline, its flights are given another of the same type if one is free. The map and the airports' timetables show what flies now — a flight just saved joins them on the day it first flies, the routes list showing it at once — and every decision that would turn flights into drafts, any airline's, lists them before it is confirmed.

An owner who appoints an operator keeps every control over the company they own: both can run it day to day, and where both change the same thing, the later decision stands. The operator still leaves the owner's own decisions — shares, dividends, appointments and the company's name — to the owner.

A world's staff can act for any company their rank reaches, an abandoned one included, exactly as its operator would: running it day to day, never dealing its shares or selling below fair value. A button asks first, and while staff act for a company that is not theirs the whole screen is bordered in red, so nothing happens by mistake. Its owner sees every change, and who made it.

The player card, opened from the button beside the search, lists the worlds you belong to above the directory of public ones, with a way to create your own. Inside a world: invitations, your name there, and the activity feed of your decisions there, each with how it went, with the staff's tools for those who hold a role. Every name can be reported, and a world's staff can keep a player out.

A world's staff — its admin and the moderators the admin appoints — have a page of their own: the requests to join, to let in or turn away, and the members, each with what the staff member's rank reaches — freezing a player, removing them, appointing a moderator. On a company's page, staff can act for it as its operator would, to open up a hub one airline has shut. World Port's developer is staff in every world, and can ban a player from all of them at once. Each act asks first, and says when it would not take effect.

Notifications live inside the game. When another player does something to you or your companies — makes an offer for your shares, takes an offer you made, asks to join a private world you run, lets you into one you asked to join, or, as staff, freezes you — that world gets a dot on your player card, and the player button a dot while any world has one. Your own decisions never mark anything.

Opening a marked world takes you to its activity feed, where each of those decisions stays for a week, even past the world's daily tidy-up, read as it was when it happened, so that you see it when you come back. The game never buzzes your phone: if you want to know what's going on, you open it.

Replaces: Notifications on your phone.

A player would have been alerted when another player's decision involved them — an offer, a change of ownership, moderation, a request to join their world — in one fixed sentence, with iOS's own Notification Center as the one list, and the phone would have warned when a bankruptcy count started and again just before its deadline.

Replaced by: Notifications.

The exchange is where deals are made: offers of shares, aircraft and leases, the ownerless ones included, and new aircraft to order by manufacturer, family and type, each with its wait. Every type has its page: its price, range, speed and running costs, and the engines and winglets it can be ordered with.

Each kind of offer has its own list, every offer standing in the world as your phone has it, with its price as things stand; one that a decision your phone has already fetched will take or withdraw is marked with the day it goes. One form accepts any of them. It states the deal from your side — what you buy, sell or lease, and from whom — with the price as the deal will work it out, your cash or, for a lease, its term and the cash it needs, and before you confirm, whether it would fail as things stand and which side fails it. Your acceptance then shows its progress on the offer, on the aircraft it brings and on the page of the company whose shares it takes.

Every company has a page anyone can open: its cash as a staircase into the weeks ahead, marked with the day it would start closing below zero and the deadline that follows, and each week's money beneath it line by line; its credit line as a gauge; and its share register as a ring with the controller marked, beside its value and share price. Its owner or operator sets its service there, and its owner alone its name, dividends and operator; a new company gets a short checklist: borrow, become an airline, order an aircraft, plan a flight.

Shares are traded from the page too. A company's owner may sell some of its shares, or a controlling block, and buy them back from its one other holder; on another company's page, bid for its shares or sell those it holds. One offer form serves shares and aircraft alike: it lists the prices you may set, can name the one company that may take the offer, shows the price as the deal itself works it out, and says before you confirm when the offer could not be taken as things stand — a line each standing offer shows under it too.

Each sitting's decisions go up to iCloud as one small record, and every phone fetches what everyone else decided and works the world forward from it. iCloud stamps each record as it arrives, and that stamp decides when a decision takes effect — the same moment on every phone. Anyone joining downloads the world's latest saved copy and catches up from there.

Every record is checked as it arrives, and one that cannot be applied is set aside rather than allowed to stop the world.

A decision made with no signal waits on the phone and goes up when a connection returns. Once a week a phone that is up to date saves a fresh copy of the world for newcomers, and a phone whose clock was set wrong learns iCloud's time from the first decision it sends, so it plays the same day as everyone else.

The map is the game's home: flights shown by their numbers in their airlines' colours, airports and bases, and a search that finds airports by their codes, names or cities. Tap an airport for its page — its hub level, its timetable, its free gates across the day, and for an airline you run its gates there, to take or give up — or a flight for its card, with its airline's name, its fares and how full each cabin is.

With it comes what every screen shares: one tray over the map that never closes, holding every page but the player card, a button for how the map looks and what it shows, a choice of which of your companies you are acting for, and one status on every decision you make — waiting to sync, then the day it takes effect, then in effect, or not, with the reason.

Pick a loop's airports on the map, and the whole flight sits on one page: its stops and their turnarounds, its days of the week, the cabin layout it flies and a fare for each cabin on each leg. A week grid picks its departure, greying the times it could not fly — a gate taken, an airport closed, no aircraft free — and saying where.

A leg at a time, its market shows as charts: who travels across the week, how attractive each hour of the day is, and how many travellers are premium, standard or budget. While a time or a fare is dragged, the planner shows the flight's projected load and profit, live — counting the decisions you have made that have yet to take effect.

Your flights are listed by route, each with its status: tap one to change it, or swipe to end it — or select several and end them at once, the gates they would give up listed before you confirm. And so that a new company can reach the planner at all, borrowing, becoming an airline and buying one of the old aircraft every world starts with come with it.

The fleet lists every aircraft by type — owned, leased out, leased in or on order — with its layout, its weekly costs and how it stands: flying, spare, on order, leased to or from whom, or on offer. Each aircraft's page holds the decisions open to it: scrap it, hand a leased one back, offer it for sale or lease and withdraw the offer, or refit it. An order's page cancels it, refunding all but a fee.

New aircraft come from the exchange, by manufacturer, family and type, each with its wait and a page of its figures. Ordering one opens the layout editor — on one of your layouts of that type, or an empty one if you have none — which builds the cabin seat model by seat model, with its engine, winglets and in-flight entertainment, showing seats, costs and how passengers will rate each class as it goes. A refit opens the same editor on the aircraft's own cabin, and charges only for what it changes.

Before any of these is confirmed, it says what it changes: the weekly maintenance, which grows with every extra aircraft family or engine you fly; the flights left with no aircraft to fly them; and the gate leases they no longer justify. An offer says it as if it were taken now.

Each city has its travellers, and each pair of cities its own tie; busy hubs draw travellers toward them, but never invent them. In each market every cabin on every flight is a choice, weighed by its fare, its comfort, its departure time, the convenience of its airports and its airline's presence there — and some travellers choose to stay home.

Every phone has to reach the same answer, so all of it is done in whole numbers and rounded once, the same way everywhere. An independent check wrote its own version of the rules from the design and matched the first version exactly on three full-size test worlds; every change since is checked against a plain reading of the rules on smaller test worlds, and a second independent reading found the code agreeing with the design at every number.

A flight leaves its base, calls at up to three more airports and comes home, on whichever days of the week its airline picks. It must be legal: within its aircraft's range, at airports able to take it, and inside each airport's opening hours. It is numbered automatically, and it locks in the earliest-delivered free aircraft of its layout.

A flight with no aircraft free is a draft — kept on the schedule, but not flying, earning or costing anything until it is edited once an aircraft is free. Changing a fare never moves a flight to another aircraft.

From landing to take-off every aircraft needs a gate. At a busy airport the gates fill up, and each weekday of each flight holds a claim, dated from when its times, its stops or its aircraft type were last set — a fare change keeps it, and a draft claims only once it has its aircraft. The earlier claim flies, and the later one waits — its whole loop, that day only — and flies again by itself once a gate frees up.

Working that out for every airport, every five minutes of the week, was the slowest part of a game day until it was rewritten: on the same full-size world, a game day that took three to five seconds now takes under one, and stays under two even when every airport has room for every flight.

A flight's running cost is worked out when it is scheduled, and does not depend on how full it is: fuel and crew for each leg, a charge at each landing, and its service on top. Every aircraft pays maintenance each week — more as it ages, and more again across a mixed fleet than a fleet of one type — and the company pays its head office and the interest on what it has borrowed.

The test flight's costs were checked by hand, to the last unit of currency.

An airline sets its service company-wide, from no frills to full service: what it serves aboard, the bags it carries free, its Wi-Fi and its crew, together, each level saying what it offers. Each level adds a percentage to the crew's cost, so it scales with the size of the aircraft and the hours it flies, and changes how passengers rate the airline's cabins.

Staff moderate. The admin and moderators approve requests to join, boot or freeze a player, hide or rename a name, and can act for a company their rank reaches as its operator would — which is how a fortress hub is opened up, its flights there ended — never dealing its shares or selling below fair value. Only the admin role passes on — to the oldest moderator, else the oldest member — and only when the admin leaves it. A booted player who asks to come back waits for staff to let them in; a frozen one can do nothing in the world, not even leave, while their companies fly on.

The developer's own account is staff in every world, above each world's admin, whether or not it is a member there — which is how a private world everyone has left can still let a player in, and how a frozen admin is set free. A ban takes an account out of every world at once, and while it lasts the account can join none; once it is lifted, the player asks again, and where the ban removed them, that world's staff decide whether to let them back in. The developer can play too, asking to join a world as anyone does.

The same account publishes which version of the game is the latest, and a phone that is behind asks its player to update.

Every phone works the world out for itself, so every phone, on every version of the game, must reach exactly the same answer. The proof is a handful of worlds, each grown from a seed: ordinary ones, and one deliberately extreme, with every price, rate and pool at the largest the game allows and airlines holding the most and least cash there can be. Each is played forward with its decisions, and every day of it, to the last passenger, the last unit of currency and the reason each decision gives, folds into one number. Every build replays them, and each number must come out as pinned. A number that moves is a mistake, unless a rule was changed on purpose.

Building it found four places where a world at the very edge of what the game allows could have stopped the app or left a save no one could load. None could happen in play; each is closed, with a test.

Running costs happen whether or not there is cash to pay them, rent included. While a company's cash is below zero, the rent it pays for an aircraft leased from another company goes to the world instead, and its lessor goes without until the company is back at zero — at most four game weeks at a stretch, since a company below zero that long goes bankrupt and the aircraft goes home. Nothing is owed, so there is nothing to track, repay or settle, and going below zero never saves a company a single ¤. And to protect those who lease aircraft out, a company can take a lease only with four weeks' rent in cash — nothing is paid up front, but a company with nothing cannot take an aircraft it could never pay for.

Replaces: Falling behind, and paying it back.

A company in trouble has four game weeks — four days of real time — to recover. If its cash closes below zero on every day of those four game weeks, it goes bankrupt; a single day at zero or above starts the count again. Nothing is sold off: its aircraft and the shares it held become ownerless and stand on offer to everyone, its orders lapse, aircraft it leased go back to their owners, its flights end and its airline code is freed. Its debts vanish with it.

Every gate starts in common use. An airline flying into an airport often enough can lease gates there: the whole gate, all day, used or not, for a weekly rent. A lease buys certainty, not a discount — a landing costs the same on your own gate as on a shared one — so, as in the real world, an airline leases where a hub is filling up and it must, not everywhere it flies.

One lease for every four daily flights — flights waiting for a gate count too, so a newcomer can fly its way into a full hub — and never more than part of an airport's gates, so a hub can be defended but never sealed shut. Taking one needs four weeks' rent in the bank. A lease its flights no longer justify ends that same day, and no flight ends with it.

Anyone can join a public world at once, unless its staff have booted them. A player picks a name for each world they join, and can change it. Only members play: someone outside a world can do nothing there but ask to join.

Leaving is a decision like any other, and it gives up every role in the world — an operator who leaves no longer runs the company. While a company's owner is out of the world, the company flies on without an owner, and the shares it holds stand on offer to everyone at its normal price; if the owner comes back while it still controls itself, it is theirs again.

Running costs happen whether or not there is cash to pay them, so a company can go below zero and fall behind on what it owes other companies — rent, mostly. What it falls behind on is owed as arrears and repaid out of what comes in, shared among those it owes, and no dividends are paid while it owes.

Replaced by: Rent while under water.

Companies lease aircraft to one another, so debts can run both ways, or round a circle of companies. Rather than cash going round and round, what they owe each other cancels down to the difference, and rent owed to a company that itself owes the payer comes off its debt instead. Rounding never pushes a company into the red: whatever it leaves over is written off.

Every phone works out the whole world for itself — a full world, as the design sizes it, is 300 airlines and some 36,000 flights — so the first thing built was a test of whether that is fast enough. A computer-generated world of full size, every market shared out between every airline, is timed one game day at a time.

On the project's small development server a full game day took from just over half a second to just under two. The measurement that counts is on a phone, and there, on an iPhone 17 Pro, a full game day takes about a quarter of a second, so catching up a missed game week takes under two seconds, the phone staying cool throughout. The phone keeps up, so the design stands; and it works out exactly the same world as the computer it was built on, down to the last passenger.

An aircraft can change hands between companies — airlines or not — outright or on a lease with a weekly rent and a term. Nobody types a price: a sale is the aircraft's fair value times one of a few fixed steps, from a nominal sum up to a premium, and a lease is always at its fair rent.

A company leasing an aircraft can hand it back before its term at no cost; while it is out on lease, it is not for sale to anyone, its lessee included, until it comes home. Every world also opens with a stock of older aircraft on sale at their book value, so a new airline can fly before its first new aircraft is built.

Companies own shares in each other. Whoever holds the most of a company's shares controls it, and its owner is the player at the top of that chain. An owner can appoint another player to run the airline day to day, and while that player runs it the owner keeps only the owner's own decisions; when the company changes hands, the appointment ends and the new owner decides who runs it. A company paying dividends shares its weekly profit out over its shares while it has the cash.

Any company can offer to buy or sell shares, or to sell or lease out an aircraft, and another accepts. Buy enough of a company's shares and you control it — and every offer the company had standing ends, as does every offer made to it alone, since its new owner made and asked for none of them. A deal priced away from fair value is refused if the side that loses by it has other shareholders or is in debt — the harm test.

Whatever has no owner — the classic stock, a bankrupt company's leftovers, the shares held by a company whose owner has left — stands on offer to everyone at full value. Shares an ownerless company holds in another company are paid for to it; for everything else, the money leaves the world.

This is the piece the rebuild exists for. A company is founded, borrows from its credit line, buys its operating certificate and orders an aircraft. The aircraft is delivered when its turn on the manufacturer's production line comes, a flight is scheduled on it, and from then on passengers choose it, it earns and pays its costs, and cash moves every day.

The test that proves it: a daily Dublin–London flight sells out at its standard fare, and its passengers fall as its fare rises to one and a half times and then twice that. Its week's revenue and costs were checked by hand, to the last unit of currency, and an independent review checked the whole loop against the design, every finding fixed.

An aircraft can be scrapped for its scrap value, or refitted with a new cabin layout — no time out of service, paid for when it takes effect. When one leaves service — scrapped, sold or handed back — its flights pass whole to the earliest-delivered spare of its type, or wait as drafts if there is none; they are never quietly cancelled.

Phones never send each other pictures of the world, only decisions: found a company, order an aircraft, schedule a flight, change a fare. Each has an exact, compact written form, and a sitting's worth travels as one small record. The saved copy of the whole world that newcomers start from has one too, written byte for byte the same by every phone that holds the same world.

The format is built to grow: a phone on an older version skips what a newer one adds rather than misreading it. And reading a record can never crash the game, whatever its bytes — the tests change every byte of a record one at a time, cut records short anywhere, and feed in random data.

The game's rules need a world to run on — cities with travellers, airports at their real positions, aircraft types with their engines and seats, and the price of everything. This is a small hand-made one, with round, plausible numbers.

It is a test bed, not the game's world: the full data, and tuning it until the game feels right, come before launch.

The board would list the companies no other company controls — a group once, not its airlines again — ordered by value, with their passengers and fleet beside them.

A rotation is a loop, and half of it was quietly failing. The flight out operated normally; the flight home was cancelled, and you were told the aircraft was already in use. It was not something you could fix by buying aircraft, re-timing the schedule or changing anything at all — on a test world with roughly eight times more aircraft than its timetable needed, every single return leg was cancelled.

The cause turned out to be the game misreading its own bookkeeping. When a departure succeeded, the code that files the outcome could not tell success from an unexplained failure, so it recorded the flight as missed and released the aircraft from the loop it had just started — orphaning every later leg. The aircraft was then genuinely unavailable to the flight home, and the reason you were shown was technically true and completely useless.

Alongside it: a turnaround is now timed from when the aircraft lands rather than from when the simulation gets round to noticing, so a schedule built on the minimum legal turn is actually flyable; an aircraft can no longer be dispatched on a leg beyond its range; and when a flight is dropped, the reason distinguishes a congested runway holding your aircraft from a genuine shortage — because those call for opposite responses and only one of them is worth spending money on.

You could already see who else flies your route and how full they are. You could not see their prices — which made it hard to tell a rival stealing your passengers on service from one simply undercutting you.

The list now counts the whole city, not just your airport. An airline flying London to Paris out of Gatwick is competing for the same passengers as one flying out of Heathrow, and the simulation has always treated them that way. The panel used to hide it. Now it says all airports and shows them together.

Setting your own fare has always worked. Reacting to someone else's did not: if a rival dropped their price and started taking your passengers, nothing happened until you noticed by hand and changed it yourself.

A route can now follow the going rate instead. Match the market, undercut it by a set amount, or deliberately price above it. Nothing stops two airlines undercutting each other into the ground — that is a decision the game lets you make, and lets you pay for.

Watching it run in a live world turned up a second problem underneath it. The “going rate” on a city pair was being learned so slowly that a brand-new route saw a market price of about a dollar, and a carrier told to match the market would have charged almost nothing for a seat. It now learns the real fare from the first day of flying, which is what makes the setting safe to use.

Short flights lose passengers to trains, and they should: on London–Paris a fast, frequent rail link takes a large share of the market, and the game models that.

The trouble was that a city's rail quality was being applied to every nearby city it flew to, whether or not a train could get there. Seoul was losing a quarter of its Shanghai and Beijing traffic to a railway across the Yellow Sea, and Tokyo–Seoul was giving up passengers to one across the Sea of Japan.

Cities now carry which surface network they sit on, so a rail alternative only counts when both ends are on it. London–Paris is untouched — the Channel Tunnel is real, and so is the competition it creates.

Every part of this project is written to a single standard, and the rule is that whoever built something is the worst judge of whether it works. So a separate pass went back over the recent work on the economy — the rewrite of how a failed airline's assets are paid out to its former shareholders, two changes to how long records are kept, and the fare mechanism above — and measured it against that standard instead of against the test suite, which was entirely green throughout.

It found real things. A retention change turned out to fix a problem that could not actually occur, while creating one that could. A safety rule that had been removed for good reasons was still described as active in a dozen places in the code, several of which had been half-updated in a way that made them read as current and correct. And the fare signal above turned out to be constant on the live world.

It also disproved three of its own findings, including one of its most alarming, by running the checks it had written down to test them — and those are recorded as prominently as the confirmed ones. A list of problems nobody has tried to knock down is not an audit; it is a list of suspicions.

Everything it found has since been fixed. The one thing it left open — why the fare signal was constant — was run as an experiment rather than argued about, and the answer was not what the audit predicted. Fares do reach the simulation correctly. What stops load factor moving is that far more passengers are being generated on some routes than really exist, so there is always someone to fill the seat. That is now understood well enough to be scoped as its own piece of work rather than guessed at, and it is described under the demand rebuild below.

Two of the fixes went further than the finding did. The stale-description problem now has an automatic check that reads every explanatory note in the code and fails the build if it names something that no longer exists — and it immediately found eighteen more that nobody had reported.

When an airline collapses, its aircraft and facilities are sold off and the money goes to whoever is owed it — lenders first, then the former shareholders. A safety check sat over that process to confirm nothing had been left behind in the middle.

The check was too strict. If anything anywhere in the world had left money stranded — a lease ending in an unusual way, weeks earlier — the check would refuse every subsequent purchase from that marketplace, permanently, with an error no player could act on and no obvious connection to the cause. A bookkeeping slip became an outage in a feature that had nothing to do with it.

It now records the problem loudly and lets the sale go through. That is the general rule the game is being held to: a hiccup is recoverable, but a mechanic that stops working is not. The same pass replaced three separate copies of the who-gets-paid logic with one — and two of them had already drifted apart, in a way that could have refunded a borrower more than the buyer paid.

Each route has a control for how aggressively its fares should follow demand — from a fixed price that never moves, to one that rises when the route is busy and softens when it is quiet. The mechanism was fully built and had nothing to read: it was being asked to compare a route's load against the load it was expected to have, which is the same number, so the answer was always "no change".

It now prices against how full that route has genuinely been over the previous game week. A week is deliberate — services run on day-of-week patterns, so a shorter window would sample Tuesdays and not Thursdays and the fare would drift on nothing more than which day the calculation ran.

A brand-new route with no history prices at its normal anchor rather than as though it were flying empty — the difference between those two readings was a fifty percent discount on every route the moment it opened.

One honest caveat, found by auditing it afterwards rather than by testing it: on the development world every flight is currently flying full, every day. A signal that never varies moves every fare by the same amount and none of them relative to each other — so the machinery is running and correct, and the effect a player would actually notice is not visible yet. Whether that is the simulation being tuned to run too hot, or simply what a capacity-starved market looks like, is an open question and the next thing to answer.

Cancelling a flight compensates the passengers you stranded, and until now it paid a flat rate per person however far they were going. That made the cheapest disruption to absorb whichever one you happened to have — a widebody left without a replacement cost an airline no more per passenger than a regional turnaround, which is not how the consequence should scale.

Compensation is now banded by distance, following the same three bands European air-passenger regulation uses and for the same reason: the further someone was going, the more it costs to put them somewhere else. Short flights pay what they always did; the longest ones pay more than twice as much per passenger.

The practical effect is that short-haul becomes the cheapest place in your network to absorb a bad day — which is where a real airline absorbs one too.

If an airline's day cannot be settled, the tick moves on rather than stalling every other airline in the world — which is right, but it used to mean the failure was a line in a log nobody was reading. Settlement now counts every airline-day it settles and every one it cannot, so a world that quietly stopped closing its books is a number that climbs rather than a silence.

A failure that has been repeating for a full game-week is reported differently from one that just started, because the first is stuck and the second is usually a retry away from fixing itself. That distinction costs nothing to make: an unsettled day already carries the date it belongs to, so how long it has been failing is simply how far behind it has fallen.

Reviewing every query that decides who gets paid, rather than only the two the report named, turned up the one that mattered: terminating an aircraft lease credited the escrow account and never drained it. Fifteen million dollars accumulated on a balance that must always read zero, which would eventually have made every seized-asset sale in that world impossible.

Also closed: settlement steps that could run twice, an insolvency check that recorded its verdict before doing the work it authorised, capital spending booked to the wrong category, and a codeshare payout that started its arithmetic from zero for a reseller who owned no aircraft.

A recurring class of bug: the interface recomputing something the server had already worked out, and getting a slightly different answer. One screen predicted an 18-hour flight the simulation actually flew in 14.

Almost every fix was a deletion. The server was already sending the right value; the client just was not reading it. Also fixed in the same pass: share prices displayed to the nearest ten million, a 200-row window presented as complete history, and a cabin-rules editor that offered four of the five cabin classes and silently destroyed any rule for the fifth when you pressed Save.

Retiring a route now also warns you what it ends — it could previously kill rotations at entirely different airports with no warning.

Four near-identical copies of the airport-authority logic became one template. Twelve copies of a content-merging loop became one. A geography helper with fifteen users was deleted outright because the standard library already did the job.

The point is the side effect. Six of those consolidations surfaced a genuine bug that the duplication had been hiding: one copy answered a different error code from its siblings, another silently overrode authored data, a spectator could not see a route's schedule, and the test data generator had been creating arrived flights with no arrival time and no cabin breakdown — which blanked the entire airport analytics screen on every test world anyone had ever looked at.

An airframe's state is what an airline actually tracks: hours flown, cycles completed, and when it was last checked. Two tiers of inspection come due on that basis — frequent light checks and rarer, far more expensive heavy ones — and an aircraft that reaches the end of its life is permanently retired.

The cabin ages separately. An interior that has not been refitted in fifteen years is worth less and sells fewer premium seats, which makes refurbishment a real investment decision rather than cosmetic.

Where the work is done matters too: your own hangar at the aircraft's own base does the job quickly, while flying a team in from another continent takes far longer. That is the payoff the maintenance facility tiers exist to sell — and getting it built was the single acceptance criterion an internal review caught as missing.

Replaces: Aircraft "condition" as a stored number.

Its replacement is dates and counters, which is what an airline's own maintenance records contain. Everything the condition number was used for — value, maintenance due, retirement — reads off those instead.

Replaced by: Maintenance — checks, life and cabin age.

There is a difference between "no aircraft is free at Heathrow this morning" — an ordinary busy day — and "this airline does not own a single aircraft of any type this rotation permits", which is structural.

The second suspends the rotation and says so. It also lifts automatically the instant the situation changes: buy the aircraft the message told you to buy, and the rotation resumes on the very next pass rather than after a lost day.

The engine was a genuine integer-programming solver. It worked, in the sense that it produced optimal assignments — but an optimiser that reshuffles your entire operation overnight is not a game mechanic players can plan around, and it required a native mathematics library that complicated every build.

Removing it made the whole system simpler in one stroke: assignment became a lookup against records the player already authored, the entire codebase became free of native dependencies, and the simulation tick got several times faster.

The lesson recorded at the time is the one worth repeating: automation executes, it never designs.

Replaced by: Rotations — you publish the timetable, the game staffs it.

Things drift. An aircraft goes into unscheduled maintenance somewhere unexpected, a rotation is retired, a base closes. Left alone, a fleet slowly ends up in the wrong cities.

A rebalancing pass notices this and dispatches empty repositioning flights to fix it. These are real flights — they appear on the map, they burn fuel, they use a runway slot — because a deadhead is a genuine operational cost and hiding it would misrepresent the cost of a messy network.

It is on this page because it is an honest part of the record. Roughly a fortnight of work was thrown away, and the replacement is better for it: the current model refuses an impossible schedule and says so, rather than quietly producing something the player never asked for.

This is the heart of the game. A rotation is a loop you write: leave your base at 07:15, fly to Munich, turn around, fly to Rome, come back — arriving home so the aircraft can do it again tomorrow. You choose the departure times, which days of the week it operates, and which aircraft types are allowed to fly it.

The game's job is then to staff that timetable from the fleet you own: every day it works out which specific airframe flies each loop. It does not invent routes for you, it does not move your departure times, and it does not decide your network. If your timetable cannot be flown with the aircraft you have, it tells you — before the flights fail — how many more you need and at which base.

That last point is why the design works. The game can predict a shortfall before anything fails to fly, so buying an aircraft is an informed decision rather than a reaction to a mess.

Because a rotation always ends where it began, the game never has to search for where an aircraft is — it already knows. That one guarantee is what let an enormously complicated optimiser be replaced by a simple lookup.

Replaces: The automatic flight-assignment engine.

The single largest performance change in the project. Deciding which aircraft flies which leg is now settled once, in advance, and written down; the simulation just looks it up.

The result is a tick that is fast, predictable, and — importantly for a shared world — does not spend its time solving the same problem repeatedly for airlines whose plans have not changed.

When an airline dies owing money, its assets get sold — but often long after the company itself has ceased to exist. Somebody still has to receive that money and pass it to the people owed it.

The answer is an estate: a frozen snapshot of who held shares at the moment of dissolution, which outlives the company and receives proceeds as its assets are realised. If a repossessed aircraft sells six weeks later, the former shareholders are still paid.

The same work separated the bank's two roles — the institution that lends you money, and the neutral party that holds seized collateral in escrow — which had been the same entity and was quietly mixing the two pots.

Rather than testing against a laptop that gets closed at night, the simulation now runs permanently on a real server with real worlds advancing in real time. Long-horizon bugs — the ones that only appear after a world has been running for weeks — surface on their own instead of being imagined.

It also means what you would see if you visited is the actual current state of the build, not a demo.

World Port installs like a native app and carries everything that is not live game data on your device: the whole interface, the entire world map and its geography, and the complete rulebook of airports and aircraft.

So it starts up on a plane, on a train, or on a bad hotel connection, and asks the network only for the things that genuinely change — your money, your flights, and what other players have done.

A large audit across airport capacity, facilities, the AI companies and the company model produced hundreds of findings, which deduplicated to 260 root causes. Every critical and high-severity one was fixed and independently verified.

This is the least visible work on this page and among the most valuable: it is the difference between a simulation that looks right for an evening and one that is still correct after a world has been running for months.

When an aircraft is due for a check, the game works down one list: your own hangar at that airport, then a partner you have a contract with, then whoever is there at walk-up rates, then the manufacturer's own network, then a last-resort fallback at a punishing price.

The ladder is the same everywhere, so the answer to "why did this cost so much" is always readable. Before this, several parts of the game each had their own opinion about the ordering.

A new world is not empty. It contains aircraft lessors with fleets to lease out, manufacturers taking orders, ground handlers at major airports and a bank that lends money — and all of them are ordinary companies in the database, subject to the same rules as a player's.

That matters more than it sounds. Because the bank is a real company with a real balance sheet, money it holds has to come from somewhere and go somewhere; because the lessors own real aircraft, the used market has genuine supply. A world with two human players still feels populated.

Failure is a process, not a deletion. A failing airline stops selling seats, finishes the flights already in the air, has its leases terminated and its collateral seized, and its remaining assets sold off. What is left is distributed to whoever held shares in it.

The wind-down deliberately cannot complete while anything is still unresolved — an aircraft mid-flight, an unsold facility, an outstanding debt — because a company that vanishes with loose ends attached breaks the world around it.

Periodically the whole build is audited by a reviewer who did not write it, hunting specifically for the kinds of bug this codebase is prone to: game-time confused with real-world time, money paths that fail open instead of closed, half-finished database transactions, and race conditions between the simulation and the API.

The findings are then deduplicated down to root causes and fixed at the source rather than patched where they were spotted. This audit found a critical one the automated checks could not: the API did not start at all under a particular configuration.

Previously every airport carried a hand-written importance tier that drove its lease pricing and authority fees. That meant a designer's guess decided how expensive a hub was, forever, regardless of what players did there.

Now it emerges: an airport that airlines genuinely build up becomes prominent, and prominence feeds back into what it costs to operate there. A quiet regional field that a player turns into a hub becomes an expensive place to be — and that is a consequence the players created.

The tier drove gate and slot lease pricing and airport-authority fees. It was removed entirely rather than kept alongside the emergent measure, because two sources for the same fact is how they end up disagreeing.

A lounge serves everybody who passes through, so modelling it per-flight was both wrong and expensive. It became a facility that accumulates usage and settles weekly — simpler, faster, and closer to how a lounge actually works.

There had been parallel lists of countries in different parts of the codebase, drifting apart from each other. They were collapsed into one, with a region derived from the country rather than stored separately — so it cannot disagree with itself.

Real aviation is full of nationality restrictions, and they shape who can buy whom. World Port models this as a default-closed rule: taking control of a licensed airline across a border is prohibited unless that country's rules allow it.

It is a genuine strategic constraint on the share market — you can hold a stake in a foreign carrier, but there is a line past which the acquisition is simply not permitted.

When you just need an aircraft somewhere else, you ferry it. It leaves, it arrives some hours later, it costs money, and it does not appear on the map or in any statistic as a revenue flight.

Deliberately, a ferry ignores aircraft range limits. That is how a short-range turboprop bought in Europe can end up flying in Hawaii, which is exactly what happens in reality — via a slow multi-stop delivery nobody wants to micromanage. Charging for it and moving on is the right level of detail.

This is a different mechanic from a repositioning flight, which is the game's own tool for correcting a fleet that has drifted out of place, and which does fly for real.

A merger moves everything the acquired airline owned onto the acquirer and dissolves the original. That includes the awkward parts: contracts where the two airlines were each other's customer, overlapping gate allotments at the same airport, and duplicate routes.

The first phase handles the mechanical transfer. What it deliberately does not yet do is tell the player what a merger will destroy before they confirm it — that is still ahead.

Unglamorous but load-bearing. A world holds millions of interlinked rows, and deleting one has to leave no dangling references anywhere. This is what makes it safe to spin up experimental or short-lived worlds and throw them away afterwards.

Money can move between the group and the companies it owns, recorded as equity rather than as revenue. That lets a player run a profitable handling business and use it to bankroll a loss-making airline — a completely legitimate strategy, and one the books now describe accurately.

An A320 can come from Hamburg, Mobile, Tianjin or Toulouse; a 737 comes from Renton. The game models that: you choose the assembly line, and the delivery flight starts from there. It is a small piece of authenticity that has real consequences for delivery cost and time.

Ordering a jet in a dense all-economy layout costs meaningfully less than the same jet with a full flat-bed business cabin. The configuration decision therefore has a capital cost as well as a revenue consequence, instead of being a free choice made after purchase.

A320, B77W, E190, AT76 — the same codes used on real flight plans and in real airline systems. Anyone who follows aviation will recognise them immediately, and it removes a whole class of invented-identifier confusion.

Freighter variants of aircraft carry cargo instead of passengers, against their own demand model and their own revenue. Cargo behaves differently from passengers — it is less schedule-sensitive and more price-sensitive — so an all-freight operation plays quite differently from a passenger airline.

Consolidated the various one-off ways things changed hands into a single marketplace with listings, and reorganised the fleet screens around the idea that an airline is a portfolio of assets — aircraft, facilities and contracts — rather than just a list of aeroplanes.

Aircraft are fitted out with a mix of First, Business, Premium, Economy and a basic-economy cabin. What you fit decides how many of each seat you have to sell, and denser layouts trade comfort for volume.

On the other side, demand is split into business, general and budget travellers who value price, schedule and comfort differently. A route full of business traffic and a route full of holidaymakers reward completely different aircraft configurations — which is the point.

The idea was that you could pay extra to be served before other airlines when a facility was busy. In practice the only thing that shipped was a doubled fee on maintenance events, with no queue or precedence logic behind it at all.

Facilities stopped being a property of your airline and became assets with their own identity. That means they can be listed on a marketplace, sold to another player, pledged as loan collateral, repossessed by the bank, or moved between sister companies in the same group.

It opens up a genuine second career path: build handling operations at busy airports and make money from other people's airlines rather than running one yourself.

Codesharing lets you sell a seat on a flight you do not operate. You request it on the route page, the operating airline approves it, and from then on your brand pulls passengers onto their aircraft with the revenue split between you.

It is genuinely useful rather than cosmetic: it lets a small airline offer destinations it could never serve profitably itself, and it gives a large one a way to fill seats it was going to fly empty.

Internally a codeshare booking is bookkeeping, not a second aircraft — an important distinction that keeps every per-flight statistic honest.

Holding capacity at an airport is not free. Each gate and slot allotment carries a weekly fee, locked in at the rate that applied when you signed, and set per-airport by whoever holds the authority role in that world.

Fall behind on those fees and your allotments are revoked automatically — which is a slower, more recoverable failure than bankruptcy, and a much more common one.

A shared persistent world needs governance. This shipped a three-tier permission system — game administrator, world administrator, and per-world staff split into moderators and airport authority — plus the surfaces they act through: grants, suspensions, an audit trail, world settings, join codes and world deletion.

The airport-authority role is the interesting one: it is a player-facing job, setting gate and slot pricing, capping frequencies and banning country pairs, rather than a hidden admin switch.

An airport can only handle so many movements an hour, park so many aircraft, and clear so many departures per runway. When demand for those exceeds supply, aircraft queue — on the ground before departure and in a hold before landing.

This is enforced at the moment a flight tries to depart or arrive, not estimated afterwards. Congestion at a hub is therefore a real operational cost that shows up as delay, and it is caused by all the airlines at that airport collectively, not just yours.

Whether you are served by a contracted partner, paying walk-up rates, or falling back on the default operator, the money moves through the same daily settlement path. Before this, one of those three routes silently charged nothing at all.

An early version moved cash around at the moment each flight landed, which made the books almost impossible to explain to a player: money appeared and vanished with no readable trail.

This inverted the model. Costs and revenue accumulate against the thing that caused them and settle on a schedule, each producing a labelled ledger row. It is why the finance screens can now tell you why you lost money last week rather than just that you did.

At an airport where you have no facilities of your own, someone has to handle your aircraft. That someone is another player's ground-services company, an independent operator, or — if nobody wants the business — a fallback provider at an unattractive price.

Contracts are open-ended and priced at signing, so a rival who builds a handling business at a busy airport before you do has genuine leverage over your costs there. This is the point at which World Port stops being a solitaire tycoon game.

It also shipped the aircraft-on-ground flow: when a jet breaks somewhere you have no maintenance cover, it sits there, earning nothing, until someone is paid to fix it.

You do not simply receive an aircraft into your fleet. It is assembled at the manufacturer's factory airfield and then has to travel to one of your bases, which takes time and costs money.

For a short-range turboprop bought for a network on the other side of the world, that is a real consideration rather than a formality.

Not every airline can afford new metal. Aircraft can be listed for sale by their owners and bought by anyone, at whatever price the market bears, with age and condition reflected in the value.

Leasing is the alternative: far less cash up front, a rent bill every week forever, and the aircraft goes back at the end. Choosing between the two is one of the sharper financial decisions in the game — and getting it wrong is one of the more common ways to go broke.

An in-world bank will lend against your fleet and facilities. How much, and at what interest rate, depends on a credit assessment of your airline: what you own, what you already owe, and whether you have been running a deficit.

Miss enough payments and the bank seizes what it lent against. That seizure path is fully modelled rather than being a game-over screen — the aircraft genuinely change hands and come back onto the market.

A player is not an airline. A player owns a group (a holding company), and that group owns companies — airlines, and later ground-handling and maintenance businesses. Each company is then activated inside a specific world.

The layering is what makes the interesting things possible later: selling a company without selling the player, moving cash between sister companies, letting one player hold a stake in another player's airline, and winding a failing airline down without deleting the person behind it.

It also shipped the universal transfer primitive — one mechanism that moves money, aircraft or facilities between any two owners — and the first version of the wind-down state machine that handles an airline going out of business.

Ground services (check-in, baggage, catering, pushback) and maintenance hangars exist at tiers. A higher tier turns aircraft around faster and does heavier maintenance work, but costs more to build and staff.

Crucially, construction is not instant — you commit money now for a capability that arrives weeks later, which is the first real forward-planning decision the game asks of you.

This also set the airline-wide catering policy: what you serve in each cabin, priced per passenger, and penalised if you promise a standard you cannot deliver.

Four payroll categories — flight crew, cabin crew, ground staff and maintenance staff — sized from what you actually operate, plus fixed weekly upkeep on every facility you own.

This is the floor under the whole economy: it is the reason an idle fleet bleeds cash, the reason overbuilding hurts, and the reason a route that merely covers its fuel is still losing you money.

Before an airline can exist, the game needs to know what an airport is. This laid down the catalogue: real-world airports with their runways, gates and the aerodrome reference code that decides which aircraft are physically allowed to operate there — a 747 cannot use an airfield built for turboprops, and the game enforces that rather than trusting the player to know.

It is deliberately shipped as authored data files rather than database tables, so the whole rulebook travels with the app and can be read on the player's own device without asking a server.