THREE years ago Ford turned its ailing AU Falcon into the $500 million BA with a revamp so complete it was essentially an all new sedan. And while sales and the brand image improved significantly, it was the quality and depth of the BA's engineering that earned this Falcon its highest praise since the 1966 XR. Now comes the BF model, with changes almost completely invisible to the eye but very obvious to the driver in terms of performance, driveability, economy and refinement. So scratch that surface because, believe it or not, the BF is another decisive step forwards for the Ford family cars.