Alrighty, here's the error report.
---- Minecraft Crash Report ----
// I just don't know what went wrong
Time: 8/22/13 8:56 PM
Description: Ticking memory connection
java.lang.NullPointerException
at co.uk.flansmods.common.DriveableData.b(DriveableData.java:66)
at co.uk.flansmods.common.EntityPlane.writeSpawnData(EntityPlane.java:151)
at cpw.mods.fml.common.network.EntitySpawnPacket.generatePacket(EntitySpawnPacket.java:123)
at cpw.mods.fml.common.network.FMLPacket.makePacket(FMLPacket.java:119)
at cpw.mods.fml.common.network.FMLNetworkHandler.getEntitySpawningPacket(FMLNetworkHandler.java:354)
at is.b(EntityTrackerEntry.java:460)
at is.b(EntityTrackerEntry.java:366)
at is.b(EntityTrackerEntry.java:449)
at ii.a(EntityTracker.java:203)
at cpw.mods.fml.common.registry.EntityRegistry.tryTrackingEntity(EntityRegistry.java:351)
at ii.a(EntityTracker.java:59)
at ij.a(SourceFile:24)
at yc.a(World.java:1554)
at in.a(WorldServer.java:865)
at yc.d(World.java:1542)
at co.uk.flansmods.common.ItemPlane.a(ItemPlane.java:63)
at ur.a(SourceFile:98)
at ir.a(ItemInWorldManager.java:348)
at iv.a(NetServerHandler.java:556)
at fk.a(SourceFile:58)
at cf.b(MemoryConnection.java:80)
at iv.d(NetServerHandler.java:136)
at iw.b(NetworkListenThread.java:57)
at bec.b(IntegratedServerListenThread.java:108)
at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:703)
at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:599)
at bdz.q(IntegratedServer.java:123)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:497)
at fy.run(SourceFile:849)