With regards to this question you posted over at Frideamon's thread (as I think it is better to answer that here)
GarryG wrote: ↑27 Oct 2021 04:04
Have planes got a dedicated height they fly?
I did a little test:
- PlanesHeightOpenTTD03.png (91.71 KiB) Viewed 2294 times
- PlanesHeightOpenTTD04.png (43.46 KiB) Viewed 2294 times
The jets I tested were roughly 187 + 16 = 203 above sealevel.
I think slower planes (propellor ones) may even fly a little lower.
So depending on the type of plane (propellor, jet, supersonic) roughly I think it is somewhere between 150 to 250 above sealevel.
Also keep in mind that it also depends on the heightlevel you place the tile containing the cloud
As the planes keep a fixed height.
Most jetplanes fly above clouds, so I would just give it a little test if i were you and place a 200 high cloud (measured from the top of the cloud) on the flightpath of various planetypes and see what happens
I think propellorplanes mostly should fly below and jets above.