An Entity type com.flansmod.common.driveables.EntityPlane has thrown an exception trying to write state. It will not persist. Report this to the mod author
net.minecraft.util.ReportedException: Saving entity NBT
at net.minecraft.entity.Entity.func_70109_d(Entity.java:1359)
at net.minecraft.entity.Entity.func_70039_c(Entity.java:1298)
at net.minecraft.world.chunk.storage.AnvilChunkLoader.func_75820_a(AnvilChunkLoader.java:346)
at net.minecraft.world.chunk.storage.AnvilChunkLoader.func_75816_a(AnvilChunkLoader.java:197)
at net.minecraft.world.gen.ChunkProviderServer.func_73242_b(ChunkProviderServer.java:256)
at net.minecraft.world.gen.ChunkProviderServer.func_73151_a(ChunkProviderServer.java:302)
at net.minecraft.world.WorldServer.func_73044_a(WorldServer.java:809)
at net.minecraft.server.MinecraftServer.func_71267_a(MinecraftServer.java:318)
at net.minecraft.server.MinecraftServer.func_71260_j(MinecraftServer.java:350)
at net.minecraft.server.integrated.IntegratedServer.func_71260_j(IntegratedServer.java:241)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:480)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)
Caused by: java.lang.NullPointerException
at com.flansmod.common.driveables.DriveableData.writeToNBT(DriveableData.java:82)
at com.flansmod.common.driveables.EntityDriveable.func_70014_b(EntityDriveable.java:157)
at com.flansmod.common.driveables.EntityPlane.func_70014_b(EntityPlane.java:73)
at net.minecraft.entity.Entity.func_70109_d(Entity.java:1342)
... 11 more

You have the same issue what I have

Is the plane from an Official pack or no?

It was a vehicle from the Modern Weapons content pack.