Got you covered
I have written a couple cover letters, and each one of them has been different.
It would seem that many individuals have a lot of different ideas about this quirky little one or two paragraph introduction.  I can't tell you I do it ‘correctly’, but I can tell you what I do and maybe some one else will pitch in.  To begin with, I find it a good idea to know whom your audience is when ever you write.  Even when you are writing to an aviation firm the guy in HR may not understand that a guy with an ATP pilot applicant is instrument proficient.  I applied for a Government position back in Feb and a month later they wrote back and stated that I did not appear to have any instrument skills and that I should read the job notice better next time.  I wrote them back, I think I had to much fun writing that letter as I have not heard back as of yet.  So if possible write the letter to a particular individual or if you cannot make sure your qualification are simple enough so that a non-aviator can understand.  That said the cover letter is simply a means of introducing yourself to a total stranger and giving him a reason to continue to your resume.  Should you not have a single argument why he should continue to your resume you have written a poor cover letter and you need to start over again.  I have heard one of my friends once say it is a sale’s pitch that sells the employer on you.  Just one word of caution don’t over do it on the accolades, keep it simple.  Think of it like an advertisement.  I bet you can tell me who the seller is if I say, “ JUST DO IT".