Terrain Flashes and becomes invisible when flying away from it

I am making flight simulator( my first Unity project) , the biggest challenge so far is terrain, so whenever I fly away from it (not that far) the terrain starts flashing and disappears which is just green mountains, so when i come back to it, i have no idea where its position is, but it suddenly appears (again flashing) when I am close , the terrain size is normal but it’s on top on a huge other terrain (about 100,000 * 100,000 which is the max),I tried changing pixel error and base map distance, no change, I looked at big terrain solutions online, but non of them really helped me, Any advice? Thanks

You need to increase camera far frustum to a bigger value. But also, you then need to try to make the near clip as far as possible (but not clip into the plane) because otherwise, the polygons far away from the camera, but close to each other will “fight” for being drawn (this is called z-fighting).

If you really need close near clip, you can use 2 cameras. The first one being near clip 0.01. far clip - 300 and make sure clear mode is set to depth only. The second camera near clip is 300, far clip is lets say 50000. Clear mode - skybox. Make sure the first camera’s depth is above the second so it is drawn over the second camera. Also, this will not work well with deferred rendering and hdr. Also, some image effects might mess things up.