Airships

"Won't catch me in one of those infernal contraptions! Work of the Mahrrus himself they are! Whats wrong with a horse, that's what I always say."  - Elderly Dwarven lady when I asked her opinions on the rise in air travel.

Airships are arguably the most wondrous of the creations which the discovery of Essence has given rise to. Airships come in many different forms - from seagoing vessels which have been repurposed and fitted with balloons and Engines, while some are purpose built, sleek vehicles constructed for war.
One key downside of air travel on Nalan compared to any other world where it has risen to similar presence is that they are hindered greatly by the strange manner in which oxygen seems to work here. This means individuals choosing to fly outside of a passenger vessel must wear a set of oxygen gear, as the air is too thin for almost any creature the breath - the exception being Goliaths, presumably due to their high altitude adaptations.
So far the this world has been somewhat fortunate in that there is impressively little conflict between any of the key Human races, and thus airships have never truly been utilised against a population during a war. That being said however especially in recent years engineers are beginning to see the potential in having a powerful military air force, especially when one's capital is a flying city. 
Regardless of their purpose, over the last 100 years airships have become an increasingly common sight above the skies of Nalan, and most major cities will have facilities for a fair number of airships to dock.

As previously mentioned, air on Nalan seems to function a little differently than air on any other world I have been to. More specifically, there seems to be a definitive cut-off point between where the air is perfectly breathable and where it is almost to thin to breathe at all. All airships tend to fly at altitudes corresponding to their function - the fastest ships (usually special order cargo or military transports) fly so high that there is so little oxygen only Goliaths are able to breathe properly there. A passenger airship on the other hand will fly at a level where it is comfortable to breathe.

High Altitude Operating Gear

(H.A.O.G)

HAOG is the general solution to the problem of high altitude travel. It essentially consists of two pressurised oxygen cannisters strapped either over the back or at the hips connected by an airtight leather tube to a fur-lined steel facemask through which the user breathes. The equipment is not enormously comfortable to wear, which is likely the reason why passenger flights take the slower option of flying at a lower level.
Since there creation roughly 15 years ago, the standard HAOG equipment has been developed extensively by Empire military technicians, and now comes as standard in naval battle armour.

The cheapest HAOG options are fairly affordable for people looking to fly at high altitudes, costing around 30 suns for a full kit. That being said these cheaper alternatives do not have reusable air cannisters, and must be replaced every time. From what I can tell, the most expensive variants cost in excess of 300 suns, and usually come as part of a full suit.

On top of breathing equipment, its also important to have particularly warm clothing, unless you happen to be a Goliath, in which case the climate at the higher end of air travel likely feels like home.