function image() { };  
image = new image(); 
number = 0;  
image[number++] = "<img src='img/Air1.gif' border='0'>" 
image[number++] = "<img src='img/Air12.gif' border='0'>" 
image[number++] = "<img src='img/Air13.gif' border='0'>" 
increment = Math.floor(Math.random() * number);  document.write(image[increment]);