The pilot radioed he was losing power and attempting a landing on a highway. According to a witness who observed the airplane as it approached an overpass, the pilot appeared to have pulled up to avoid power lines, and then collided with a telephone line. The airplane impacted onto a median strip. The induction air box door spring was found to have worn completely through the attach hole of the air box door arm. The total spring length was 2.50 inches; engineering drawing specifies a spring length of 3.66 inches. Also, the thickness of the arm itself was less than 50% of that specified by the drawing. The bracket that the other end of the spring attaches to was mislocated about 0.50 inch from the drawing dimension. In addition, the air box was fastened together mostly by blind fastener rivets which are not called for on the drawing. It was also caulked with a soft sealant also not called for.