Rules of Aether Travel

In the Aether, the vast ocean of magic that separates Orphan’s splinters, there is no air. All the same, humans can safely traverse the Astral Sea wearing no special gear. How?
The Aether has no air, but nor does it exactly have a lack of air. It is not reality, but raw potentiality, and it operates on the logic of faith. A person has certain beliefs, ingrained on the instinctual level—if I jump, I’ll come back down; if I breathe, my lungs will fill with air—and the Aether conforms to these beliefs. You create your own gravity; you breathe in the Aether’s raw spellstuff, and by the time it reaches your lungs it has become air.
This is why, on aether stations with large populations, the Aether tends to act in a way reminiscent of stable reality. The collective belief of a large population imposes a facsimile of reality. Out in the open vastness of the Astral Sea, such strictures do not always apply. Due to the surreal nature of Aether travel, it comes with a handful of special rules, as seen below.

General Rules

• Negation. While in the Aether, you can consciously suspend your instinctive beliefs, thus allowing you to alter aspects of your pocket of self-imposed reality. This discipline, known as negation, is an act of mental legerdemain which even seasoned aethernauts may find challenging, and which can rarely be sustained for longer than a few seconds at a time. The most common use of negation is to reverse the effects of gravity, allowing one to float, but you might use it to do other things; I’ll adjudicate such cases as they arise.
• Floating. To float, you must spend your reaction to make a DC 10 Intelligence check. At the beginning of each of your subsequent turns, you must spend your reaction to repeat this check. As long as you succeed on these checks, you gain a flying speed equal to your walking speed. You stop floating when you fail one of your checks or when you choose to stop floating as a free action. Most aethernauts float only when it’s absolutely necessary, preferably while tethered to their ship. The Aether is a dangerous place. Falling overboard is undesirable.
• Flight. While in the Aether, spells and effects that grant flight work as normal. Feather fall, rather than slowing your fall, stops it outright and lets you hover in place for the spell’s duration. For this reason, a potion or scroll of feather fall is part of many aethernauts’ kits.
• Teleportation. Long-range transport spells (gate, plane shift, teleport, teleportation circle, transport via plants, and word of recall) can be used to travel between splinters, thus forgoing the need for Aether travel entirely.

Aetherships

An aethership is a vessel that has been enchanted with the ability to traverse the Aether. Aetherships vary hugely in terms of construction and appearance: some are elaborate and opulent vessels, constructed painstakingly and at great cost, while others are little more than ramshackle assemblages of debris.
An aethership is steered by means of an arcane helm, a mystical device powered by the Aether’s ambient magic. A person operating an aethership’s arcane helm is called a pilot.
Aetherships are mechanically very simple. A typical aethership’s stat block lists its armor class, hit points, and damage threshold, as well as its immunities. Most aetherships have immunity to poison and psychic damage, and to all conditions save for grappled, invisible, and restrained. Aetherships have no ability scores; if a ship would make an ability check or saving throw, its pilot makes a roll instead, usually either an Intelligence (Arcana) check or an Intelligence saving throw.
If an aethership sustains damage, its crew can repair it. During travel, this is a slow and cumbersome process, which restores the ship’s hit points by 1d4 per day and crew member doing repairs. Stopping the ship increases this amount to 2d4, but drifting in the Aether is a risky prospect. Finding an aether-haven and hiring professionals to handle the repairs costs money, but is much faster and safer.

The Helm

An arcane helm is a product of Valqari engineering: a column of some durable material, varying in size but usually taller than a person, inscribed with magical runes. An aethership’s helm is simultaneously its engine and its method of steering.
To operate an arcane helm, you must use an action to connect to it. To do so, you must be standing within 5 feet of the helm. Connecting to the helm requires concentration; if you cast a spell which requires concentration, or fail a concentration saving throw, the connection ends. Once you’ve connected to the helm, you do not need to stay near it to maintain the connection, but if you leave the ship, the connection ends. While connected to the helm, you can use an action to touch a willing creature and transfer the connection to it.
You can challenge a pilot for control of their helm. To do so, you connect to the helm as usual; this triggers an Intelligence (Arcana) contest between you and the pilot. If the pilot is not within sight of the helm, they have disadvantage on their roll. The winner of the contest connects, or maintains their connection, to the helm. The loser takes psychic damage equal to the difference between the rolls.
While connected to an arcane helm, you sense the nearest pharoi, and you can use your action to set your ship traveling towards one of them. You can also use your action to perform smaller-scale maneuvers. Usually such maneuvers succeed automatically; where fancy flying is required, you might have to make an Intelligence (Arcana) check.
While within 30 feet of an arcane helm, you can use a bonus action to feed a spell slot of any level into the helm. Doing so supercharges the helm until the start of your next round, and gives the pilot advantage on one roll made to pilot the ship. You don’t have to be connected to the helm to do this.

Other Actions

The pilot is not the only member of an aethership’s crew. On some smaller aetherships, the pilot is also the captain, but many larger ships have both a pilot and a captain. An aethership might have a small crew sharing the various duties aboard, or it might have dedicated jobs: gunners, lookouts, guards, surgeons, cooks, and so forth. Performing these roles is less elaborate than piloting the ship, and usually comes down to making skill checks to perform certain actions.
Here are some other actions you might perform during combat:

• Command. You can command a creature aboard your ship to perform some action. This is a free action. The creature must be able to hear you and comprehend your orders, and your orders must be succinct enough to be conveyed in a turn. You might need to make a Charisma (Persuasion) check to convince the creature to heed you if your orders are potentially dangerous or the creature is otherwise disinclined to obey you.
• Fire cannon. Firing a thaum cannon or other shipboard weapon is an action which requires a Dexterity-based attack roll.
• Survey. In a battle or other dangerous situation, lookouts are invaluable. You can spend an action to survey the scene and convey this information to a creature of your choosing. To do so, you must succeed on a Wisdom (Perception) check (DC varies), and the creature must be able to hear your words. The creature gains advantage on an ability check, skill check, or attack roll made while acting on your information before your next turn.