diff --git a/newgrf.c b/newgrf.c
--- a/newgrf.c
+++ b/newgrf.c
@@ -589,15 +589,15 @@ static bool AircraftVehicleChangeInfo(ui
 		case 0x09: {	/* Helicopter */
 			FOR_EACH_OBJECT {
 				uint8 heli = grf_load_byte(&buf);
-
-				avi[i].subtype = (heli == 0) ? 0 : 1;
+				avi[i].subtype &= ~0x01; // remove old property
+				avi[i].subtype &= (heli == 0) ? 0 : 1;
 			}
 		}	break;
 		case 0x0A: {	/* Large */
 			FOR_EACH_OBJECT {
 				uint8 large = grf_load_byte(&buf);
-
-				avi[i].subtype = (large == 1) ? 3 : 1;
+				avi[i].subtype &= ~0x02; // remove old property
+				avi[i].subtype &= (large == 1) ? 2 : 0;
 			}
 		}	break;
 		case 0x0B: {	/* Cost factor */