Oh to have a BMI of 19
I reckon you'll be right mate. It is a bit of a sledgehammer tool this BMI, and as bronco says there are many elite sports people ie basketballers, marathon runners, pole vaulters, weight lifters and rugby players who would be classified as either anorexic or morbidly obese according to the scale.
In terms of airline jobs though, I would suspect that in any case it's far better to be athletically fit and BMI 19 than a big not-exercising pork-pie-scoffing 35 or 38. It's my impression that those who use it, do so more as a preliminary screener to find out the massively overweight types who are at increased risk of early retirement due heart disease - they just want to make sure that they aren't going to spend all this money on you and then you go and lose your medical just as you're about to make your command or something like that.