Air Combat (Long War)
UFOs are tougher, faster, and much more deadly in the Long War. Along with that, your crafts and armaments are significantly less potent, at least at first. You'll be needing to cycle your craft regularly (like your soldiers), as kills now grant a sort of XP to accuracy, as if your pilots learn UFO flight patterns and movements, and learn to fire with increasing accuracy with their experience. Interceptor experience provides +3% to hit per kill (up to + 30%) and +1% damage per kill (with no top limit). Also, you will find that both your craft and UFOs may sometimes get 'critical hits', with UFOs being downed in a few hits, or your undamaged Interceptor immediatly going into near-full red.
For starters, the Avalanche Missiles, on your fresh pilots, now have an abysmal 40% accuracy. While it is possible to still down the first Scout with one Interceptor, this is incredibly unlikely, and most likely it will take two, or even three interceptions to bring down these upgraded craft.
Of course, with the vastly greater number of UFOs you will encounter being a factor, repair times may cripple you: for example, since you will lose at least 1 country in the first month, that continent will most likely be the one to be focused on for Terror missions and UFO flights, which will damage your craft-- which will then raise panic, and in turn, cause more alien attacks to occur on that continent, to which you cannot intercept in flight.
UFOs can fly at three altitudes. The altitude is a clue of what mission the UFO is going on: "High," "Low," and "NOE," ("Nap of the Earth,"). UFOs flying at NOE altitude are most likely to land, are performing bombing runs, or will generate an Abduction or Terror mission immediately upon arriving at their destination. UFOs at high altitude are most likely to be hunting satellites.
The LW mod brings back a mechanic from previous generations of XCOM: UFOs can now have full DOA crashes (with minimal Alloy recovery, and no corpses or other artifacts), so in some cases you may want to pull your punches. To compensate, the Council will give cash rewards for UFOs obliterated in flight. This will most commonly be the case for high altitude UFOs, as the fall from sub-orbital flight will demolish almost all other material of use from a crash.
Satellite-hunting UFOs might be dissuaded by launching and at least damaging them, as if the aliens abort their mission to return for repairs. And in general, you should send at least one interceptor after a UFO (and avoid damage in turn), as this show of force will reduce the Panic levels gained from the general public, even if a given UFO is far out of your league at that point.
You may now also set a combat stance for your interceptors as they launch on a mission. Aggressive gives +15% to hit for both you and the UFO; balanced plays out like normal, and Defensive gives -15% to hit for both you and the UFO. You may not use the dodge consumable when aggressive and you may not use the auto-hit consumable when defensive.
Lastly, there are Research and Engineering projects that will assist in aerial sorties. The three modules remain, but with Aim being built from Floater corpses (so you may want to keep a good number on hand, at least to help your less experienced pilots), the Boost device from Drone wrecks (primarily useful for close-range weapons, but as the elongated time may work against you, in terms of damaged and destroyed interceptors (at least at first)), and the useful Dodge module being limited by how many Cyberdiscs you can encounter and destroy.
Once, through landing or shooting it down, that you successfully raid a UFO type, you can research that craft type for a damage bonus against it in future encounters.
Lastly, there are several Foundry projects that will vastly improve your crafts stats all around.
As you progress, each type of UFO's statistics also increase, from general 'health' to firing rates, as to keep you on your toes; so don't expect to every truly dominate the skies. Plus with the added variables to air-interception, there is no clear-cut "UFO X can be brought down by Interceptor Y" table. As such, the Long War's UFO page will be your general guide for how--- or if-- to attempt to engage these potent UFOs.