Why a container has a sloping corner | How map.flights was built

A round hold

The fuselage of an airliner is roughly a tube. A floor splits it into two storeys: passengers sit upstairs, and downstairs is the hold for suitcases, mail and freight. So the hold sits in the bottom part of a circle, where the walls curve in towards each other, and a square crate would leave empty corners on both sides.

That is why the most common aircraft container, the LD3 with the code AKE, has one bottom corner cut off. At the top it is 201 centimetres wide, at the floor only 156. In the hold they stand in pairs, straight sides together and the sloping corners out towards the fuselage walls, and a pair fills the curve almost to the last centimetre. A passenger 777-300ER takes 44 of them under its floor.

It works that way in 3D too. Two containers that stood side by side in the aircraft ride the train as mirror images: one has its sloping corner on the left, the other on the right.

Diagram of two fuselage cross-sections seen from behind. On the left a widebody: at the bottom two containers with their bottom corners cut off towards the walls, above them a container and a pallet with their outer top corners cut off. On the right a narrowbody: at the bottom a low container cut off on both bottom corners, above it a container cut off on both top corners — A cross-section through a freighter, seen from behind. On the left a widebody: two LD3s in the hold, a container and a pallet on the main deck. On the right a narrowbody with a low AKH below and an AAY above. A diagram, not to the scale of any particular type; the containers are the same models you see on the map.

There are more kinds. An AKE is closed either with a curtain or with a solid door, an AKN has pockets for forklift tines in its base, and an RKN is the refrigerated one. The hold of the A320 family takes the low AKH, 114 centimetres tall and cut off on both bottom corners. The long LD6, coded ALF, spans the whole width of the hold and has both corners cut off as well. The ALP keeps its corners square.

Every container carries a label on its side with its type and a four- or five-digit number, followed in real life by the code of the airline that owns it. In 3D the label shows the airline of the aircraft carrying it.

An AKE container on a dolly, dark grey with an orange curtain across the front; the bottom corner on the curtain side is cut off — Containers for the hold, each on its own dolly. The numbers on the labels are illustrative.

An AKE container on a dolly, light grey with a solid door and red latches; one bottom corner cut off — Containers for the hold, each on its own dolly. The numbers on the labels are illustrative.

Upstairs it’s the other way round

A freighter has no passenger cabin. In its place is the main deck, a long empty hall with rollers in the floor, and it sits in the widest part of the fuselage. The floor there is flat and wide, but overhead the walls curve in towards the ceiling. So containers for the main deck have a top corner cut off.

A 747 or a 777 takes two rows side by side. The AMJ container, 244 centimetres tall, has only its outer top corner cut off, the one by the wall. In the narrower fuselage of a 757 or a 737 there is room for a single row across, so the AAY has both top corners cut off. The square AMA only goes where there is enough room overhead.

Pallets for the main deck are built up to the same outline. The people stacking the freight have a template in the shape of the fuselage, and anything that sticks out gets restacked. That is why a pallet of boxes next to an AAY has the same sloping top corners as the container.

A tall grey AMJ container on a dolly; one top corner along its length is cut off — Containers and a pallet for the main deck. The numbers on the labels are illustrative.

An AAY container on a dolly with a dark blue curtain at the front; both top corners are cut off, so the front looks like the gable of a house — Containers and a pallet for the main deck. The numbers on the labels are illustrative.

Everything under a net

A lot of freight doesn’t go into a container. A crate with a machine in it, drums, tyres or a heap of boxes are stacked on a flat aluminium pallet, a sheet 318 by 244 centimetres, and a net is stretched over the lot. Along the bottom it hooks into a rail around the edge of the pallet. If the aircraft has to brake hard or flies through turbulence, nothing slides off.

In 3D loose freight always has a net, one over the whole pallet. It is usually dark, like most real ones, pulled tight over the tops of the boxes and around the drums and tyres, and drawn down to the rail at the bottom. Over dark film it turns lighter or coloured so you can see it.

And no pallet is like the next. How many drums, how many tyres, how tall the crate is and what colour the film is gets decided by a draw made once for every piece. The same piece then looks the same in the door, on the loader’s platform and on the dolly, and another aircraft carries a different load.

A pallet piled with cardboard boxes of different sizes under a dark net hooked to the edge of the pallet — Pallets for the main deck. Every one has a net over the whole load, drawn down to the rail along the edge.

A pallet with a large crate, a black drum and blue drums, all under one dark net — Pallets for the main deck. Every one has a net over the whole load, drawn down to the rail along the edge.

Trains at the nose

A factory-built 747 freighter has a nose that swings up. A loader pulls up in front of it, a platform on scissors with a bridge, and a train of dollies behind a tug comes alongside. Piece by piece the freight rolls out of the aircraft onto the bridge, the platform takes it down and it rolls off onto a dolly. A full train drives away and an empty one arrives. The same happens at the side door and at the holds, where LD3s travel.

In its turnaround chart Boeing counts 30 pieces on the main deck of a 747-400F and five pallets and 16 containers in the holds. The main deck of a 777F is filled only through the side door behind the wing and takes 27 pallets. The counts come from the documents manufacturers publish for airports.

Children watch the map too. Even though it is only a simulation of what is probably happening on the stand, we try to make it worth watching and fun, and in the end not just for children. If it isn’t for you, the “Aircraft servicing” button in the 3D view controls switches off the whole display of freight and of passengers getting on and off.

A freighter 747 from above and behind on a remote stand: the nose raised with a loader and a train of dollies in front of it, more loaders and a train at the side, buildings of the cargo area behind — A freighter 747 on a remote stand, with loaders and trains at the nose and along the side. The aircraft is illustrative. Map data © OpenStreetMap contributors.

The detail comes when you zoom in. Close up the containers have ribs, a frame, a curtain with straps and a label with a code, and the pallets have boxes and a net. From further away only the shape and the colour are left, and from far away a plain box. A big cargo airport with dozens of aircraft on its stands doesn’t slow down because of it.

At night the same train works in the dark, with amber beacons flashing on the tug and the loader.

A freighter 777 from the side with its side door open behind the wing; below it a tug with a train of five dollies: pallets of boxes under nets, a green net and a green container — Trains of containers and pallets at a 777F and a 747-400F, by day and at night. The aircraft are illustrative. Map data © OpenStreetMap contributors.

The same freighter 777 and its train of pallets at night, a beacon lit on the tug — Trains of containers and pallets at a 777F and a 747-400F, by day and at night. The aircraft are illustrative. Map data © OpenStreetMap contributors.

A container for the hold has a sloping bottom corner, one for the main deck a sloping top corner. On our map you can tell which way each one is going.