Remove hardcoded constant from Fly.

OpenRA.Mods.Common/Activities/Air/Fly.cs

@@ -66,9 +66,11 @@ namespace OpenRA.Mods.Common.Activities
 			if (insideMaxRange && !insideMinRange)
 				return NextActivity;
 
-			// Close enough (ported from old code which checked length against sqrt(50) px)
 			var d = target.CenterPosition - self.CenterPosition;
-			if (d.HorizontalLengthSquared < 91022)
+
+			// The next move would overshoot, so consider it close enough
+			var move = plane.FlyStep(plane.Facing);
+			if (d.HorizontalLengthSquared < move.HorizontalLengthSquared)
 				return NextActivity;
 
 			// Don't turn until we've reached the cruise altitude