--- a/src/ai/default/default.cpp	Sat Feb 10 00:22:32 2007 +0000
+++ b/src/ai/default/default.cpp	Sat Feb 10 08:19:39 2007 +0000
@@ -3323,10 +3323,11 @@
 
 static int32 AiDoBuildDefaultAirportBlock(TileIndex tile, const AiDefaultBlockData *p, byte flag)
 {
+	uint32 avail_airports = GetValidAirports();
 	int32 total_cost = 0, ret;
 
 	for (; p->mode == 0; p++) {
-		if (!HASBIT(_avail_aircraft, p->attr)) return CMD_ERROR;
+		if (!HASBIT(avail_airports, p->attr)) return CMD_ERROR;
 		ret = DoCommand(TILE_MASK(tile + ToTileIndexDiff(p->tileoffs)), p->attr,0,flag | DC_AUTO | DC_NO_WATER,CMD_BUILD_AIRPORT);
 		if (CmdFailed(ret)) return CMD_ERROR;
 		total_cost += ret;

--- a/src/airport.cpp	Sat Feb 10 00:22:32 2007 +0000
+++ b/src/airport.cpp	Sat Feb 10 08:19:39 2007 +0000
@@ -447,13 +447,16 @@
 
 uint32 GetValidAirports(void)
 {
-	uint32 bytemask = _avail_aircraft; /// sets the first 3 bytes, 0 - 2, @see AdjustAvailAircraft()
+	uint32 mask = 0;
 
-	if (_cur_year >= 1980) SETBIT(bytemask, 3); // metropolitan airport
-	if (_cur_year >= 1990) SETBIT(bytemask, 4); // international airport
-	if (_cur_year >= 1983) SETBIT(bytemask, 5); // commuter airport
-	if (_cur_year >= 1976) SETBIT(bytemask, 6); // helidepot
-	if (_cur_year >= 2002) SETBIT(bytemask, 7); // intercontinental airport
-	if (_cur_year >= 1980) SETBIT(bytemask, 8); // helistation
-	return bytemask;
+	if (_cur_year <  1960 || _patches.always_small_airport) SETBIT(mask, 0);  // small airport
+	if (_cur_year >= 1955) SETBIT(mask, 1); // city airport
+	if (_cur_year >= 1963) SETBIT(mask, 2); // heliport
+	if (_cur_year >= 1980) SETBIT(mask, 3); // metropolitan airport
+	if (_cur_year >= 1990) SETBIT(mask, 4); // international airport
+	if (_cur_year >= 1983) SETBIT(mask, 5); // commuter airport
+	if (_cur_year >= 1976) SETBIT(mask, 6); // helidepot
+	if (_cur_year >= 2002) SETBIT(mask, 7); // intercontinental airport
+	if (_cur_year >= 1980) SETBIT(mask, 8); // helistation
+	return mask;
 }

--- a/src/engine.cpp	Sat Feb 10 00:22:32 2007 +0000
+++ b/src/engine.cpp	Sat Feb 10 08:19:39 2007 +0000
@@ -69,18 +69,6 @@
 	LoadCustomEngineNames();
 }
 
-static void AdjustAvailAircraft(void)
-{
-	byte avail = 0;
-	if (_cur_year >= 1955) avail |= 2; // big airport
-	if (_cur_year <  1960 || _patches.always_small_airport) avail |= 1;  // small airport
-	if (_cur_year >= 1963) avail |= 4; // enable heliport
-
-	if (avail != _avail_aircraft) {
-		_avail_aircraft = avail;
-		InvalidateWindow(WC_BUILD_STATION, 0);
-	}
-}
 
 static void CalcEngineReliability(Engine *e)
 {
@@ -178,8 +166,6 @@
 		 * but using this, you can ask what type an engine number is
 		 * even if it is not a vehicle (yet)*/
 	}
-
-	AdjustAvailAircraft();
 }
 
 static void AcceptEnginePreview(EngineID eid, PlayerID player)
@@ -371,7 +357,6 @@
 			}
 		}
 	}
-	AdjustAvailAircraft();
 }
 
 /** Rename an engine.

--- a/src/misc.cpp	Sat Feb 10 00:22:32 2007 +0000
+++ b/src/misc.cpp	Sat Feb 10 08:19:39 2007 +0000
@@ -310,7 +310,7 @@
 	    SLEG_VAR(_tick_counter,           SLE_UINT16),
 	    SLEG_VAR(_vehicle_id_ctr_day,     SLE_UINT16),
 	    SLEG_VAR(_age_cargo_skip_counter, SLE_UINT8),
-	    SLEG_VAR(_avail_aircraft,         SLE_UINT8),
+	SLE_CONDNULL(1, 0, 45),
 	SLEG_CONDVAR(_cur_tileloop_tile,      SLE_FILE_U16 | SLE_VAR_U32,  0, 5),
 	SLEG_CONDVAR(_cur_tileloop_tile,      SLE_UINT32,                  6, SL_MAX_VERSION),
 	    SLEG_VAR(_disaster_delay,         SLE_UINT16),

--- a/src/oldloader.cpp	Sat Feb 10 00:22:32 2007 +0000
+++ b/src/oldloader.cpp	Sat Feb 10 08:19:39 2007 +0000
@@ -1431,7 +1431,7 @@
 	OCL_VAR (  OC_UINT8,    1, &_economy.infl_amount ),
 	OCL_VAR (  OC_UINT8,    1, &_economy.infl_amount_pr ),
 	OCL_VAR (  OC_UINT8,    1, &_economy.interest_rate ),
-	OCL_VAR (  OC_UINT8,    1, &_avail_aircraft ),
+	OCL_NULL( 1 ), // available airports
 	OCL_VAR (  OC_UINT8,    1, &_opt.road_side ),
 	OCL_VAR (  OC_UINT8,    1, &_opt.town_name ),
 

--- a/src/variables.h	Sat Feb 10 00:22:32 2007 +0000
+++ b/src/variables.h	Sat Feb 10 08:19:39 2007 +0000
@@ -50,9 +50,6 @@
 // Skip aging of cargo?
 VARDEF byte _age_cargo_skip_counter;
 
-// Available aircraft types
-VARDEF byte _avail_aircraft;
-
 // Position in tile loop
 VARDEF TileIndex _cur_tileloop_tile;