Return error when instructed to takeoff twice - Fixes #579
Return error when instructed to takeoff twice - Fixes #579

erikquinn/atc,tedrek/atc,tedrek/atc,luznicky/atc,luznicky/atc,luznicky/atc,erikquinn/atc,jpeterson1346/atc,jpeterson1346/atc,jpeterson1346/atc,erikquinn/atc,tedrek/atc