Hope I'm not teaching anybody to suck eggs here, but if you don't follow up your CV/letter with a phone call or personal visit to gauge the level of interest and to check on progress, then the airlines may well be justified in thinking you showed as much interest as they seem to be showing in you.
That advice is as true in any job hunt as it is in aviation. Don't forget, most of these letters and CV's end up on a pilot's desk, whose primary task is not admin, and they aint going to take time out of a busy schedule to reply to random applications. If you take the time to make it personal in a face-to-face kind of way, then you are far more likely to at least get a sympathetic and personal "**** off, we're not interested". My experience at least.
