Now we all know for sure that in 2020 we're gonna have Legs AND Atmospheric Planets 
Jokes aside, here is a proposal for the Atmospheric Transition in case Atmospheric Planets will ever be taken into consideration.
LANDING ON AN ATMOSPHERIC PLANET
The ships need to be equipped with an advanced planetary landing module that allows to land on airless and atmospheric planets (this replaces the old one). This module allows also the ship to fly on the planet surface at regular speeds, like in the void, even in thick and dense atmosphere ignoring the air drag. The fuel consumption is eventually increased but it is such a low difference that it can be negligible (or taken into consideration in case FDEV decides to make a more complex fuel consumption model).
The initial approach to the planet and its exclusion zone is like any regular airless planet, with speed automatically limited at 200 km/s.
Crossing the mesosphere the ship will start making glowing/burning effects and the heat levels will rise at the fix value of 60%. The ship will also experience vibration and heavy turbulence. The speed will be reduced automatically by the FSD like approaching an airless planets.
Glide Phase 1: it starts entering the stratopause (ELW and WW is around 50 km altitude). Speed is limited at 5 km/s and the heat level rises to 70%. In this phase it is mandatory to keep the ship pitch in a range between -45° and -30°. There will still be turbulence during this transition so it would require constant input from the player to keep the ship in the appropriate range. This Glide Phase can’t be interrupted, if you fail to keep the attitude the ship will start heating up.
You can eventually sink down with a pitch of -90° but the heat levels will immediately jump to values higher than 500% (for example). If your pitch is higher than -30° the FSD will have to correct the ship drift generated by the atmospheric drag (explanation for the lore) so it will heat up again. If you pitch above 0° you climb again to orbit and the heat level will fix again at 70%. Glide Phase 1 ends reaching the Tropopause (around 20km altitude for ELW and WW). According to the math this phase is 10 seconds long.
Glide Phase 2: in the Troposphere we have the meteorological phenomena with jet streams at high altitude, rain, clouds and winds. Atmospheric transition is over so there's no more risk of overheating. The ship slows down to 2.5 km/s fixed. Here you have no more pitch limitations, except that if you pitch above -5° the glide stops. You can use this phase to correct your route in case you overshot your destination or you’re still far from it because of the limitations of phase 1. The ship can experience strong turbulence because of high altitude jet streams or dense clouds. Phase 2 ends at 5 km altitude.
Normal Flight Mode
Since our ships fly as bricks with powerful thrusters and they have the advanced atmospheric module installed the aerodynamics do not really affect the flight except for the winds because the ship is completely immersed in the atmospheric fluid. Like in normal aircrafts the wind speed and direction could speed up or slow down our maximum speed. If we have head wind we may decide to fly closer to the ground where this is weaker. If we have tail wind we may decide to fly at high altitude to get some real boost from the jet streams. The drift caused by the lateral wind is instead corrected by the Flight Assist.
The ship is also exposed to all strong environmental phenomena like thunderstorms and turbolence through the thick clouds.
Leaving an atmospheric planet
It’s not possible to high-wake from the troposphere. If the troposphere is thin you can cross it in normal flight and then high-wake from the stratosphere in Normal Flight mode without overheat issues. Otherwise you can low-wake in Supercruise at 2.5 km altitude. Speed is limited to 2.5 km/s until you reach the stratosphere. Ship is still affected by strong turbolence crossing the high altitude jet streams.
Once in the stratosphere the ships accelerate up to 5 km/s and the Heat Level rise again to 70%. Now it is possible to high-wake if your ship does not overheat easily. Otherwise you need to wait to a bit more to have a clean High-Wake.
In the stratosphere supercruise, if you decide to go back to the planet surface as soon as you sink down below 0° pitch the ship will automatically go into Glide Phase 1, so you‘ll have to control the ship in the correct pitch range again (-45°-30°) to avoid overheat.
Once the ship is out of the stratosphere and into the mesosphere the heat level reduces again to 60%. The ship behaves like leaving an airless planets, so accelerating as the altitude increases and the ship goes into orbital flight mode. Once out of the stratosphere the heat level returns to the regular value.
TO RESUME:
Jokes aside, here is a proposal for the Atmospheric Transition in case Atmospheric Planets will ever be taken into consideration.
LANDING ON AN ATMOSPHERIC PLANET
The ships need to be equipped with an advanced planetary landing module that allows to land on airless and atmospheric planets (this replaces the old one). This module allows also the ship to fly on the planet surface at regular speeds, like in the void, even in thick and dense atmosphere ignoring the air drag. The fuel consumption is eventually increased but it is such a low difference that it can be negligible (or taken into consideration in case FDEV decides to make a more complex fuel consumption model).
The initial approach to the planet and its exclusion zone is like any regular airless planet, with speed automatically limited at 200 km/s.
Crossing the mesosphere the ship will start making glowing/burning effects and the heat levels will rise at the fix value of 60%. The ship will also experience vibration and heavy turbulence. The speed will be reduced automatically by the FSD like approaching an airless planets.
Glide Phase 1: it starts entering the stratopause (ELW and WW is around 50 km altitude). Speed is limited at 5 km/s and the heat level rises to 70%. In this phase it is mandatory to keep the ship pitch in a range between -45° and -30°. There will still be turbulence during this transition so it would require constant input from the player to keep the ship in the appropriate range. This Glide Phase can’t be interrupted, if you fail to keep the attitude the ship will start heating up.
You can eventually sink down with a pitch of -90° but the heat levels will immediately jump to values higher than 500% (for example). If your pitch is higher than -30° the FSD will have to correct the ship drift generated by the atmospheric drag (explanation for the lore) so it will heat up again. If you pitch above 0° you climb again to orbit and the heat level will fix again at 70%. Glide Phase 1 ends reaching the Tropopause (around 20km altitude for ELW and WW). According to the math this phase is 10 seconds long.
Glide Phase 2: in the Troposphere we have the meteorological phenomena with jet streams at high altitude, rain, clouds and winds. Atmospheric transition is over so there's no more risk of overheating. The ship slows down to 2.5 km/s fixed. Here you have no more pitch limitations, except that if you pitch above -5° the glide stops. You can use this phase to correct your route in case you overshot your destination or you’re still far from it because of the limitations of phase 1. The ship can experience strong turbulence because of high altitude jet streams or dense clouds. Phase 2 ends at 5 km altitude.
Normal Flight Mode
Since our ships fly as bricks with powerful thrusters and they have the advanced atmospheric module installed the aerodynamics do not really affect the flight except for the winds because the ship is completely immersed in the atmospheric fluid. Like in normal aircrafts the wind speed and direction could speed up or slow down our maximum speed. If we have head wind we may decide to fly closer to the ground where this is weaker. If we have tail wind we may decide to fly at high altitude to get some real boost from the jet streams. The drift caused by the lateral wind is instead corrected by the Flight Assist.
The ship is also exposed to all strong environmental phenomena like thunderstorms and turbolence through the thick clouds.
Leaving an atmospheric planet
It’s not possible to high-wake from the troposphere. If the troposphere is thin you can cross it in normal flight and then high-wake from the stratosphere in Normal Flight mode without overheat issues. Otherwise you can low-wake in Supercruise at 2.5 km altitude. Speed is limited to 2.5 km/s until you reach the stratosphere. Ship is still affected by strong turbolence crossing the high altitude jet streams.
Once in the stratosphere the ships accelerate up to 5 km/s and the Heat Level rise again to 70%. Now it is possible to high-wake if your ship does not overheat easily. Otherwise you need to wait to a bit more to have a clean High-Wake.
In the stratosphere supercruise, if you decide to go back to the planet surface as soon as you sink down below 0° pitch the ship will automatically go into Glide Phase 1, so you‘ll have to control the ship in the correct pitch range again (-45°-30°) to avoid overheat.
Once the ship is out of the stratosphere and into the mesosphere the heat level reduces again to 60%. The ship behaves like leaving an airless planets, so accelerating as the altitude increases and the ship goes into orbital flight mode. Once out of the stratosphere the heat level returns to the regular value.
TO RESUME:
