When shooting in the sky you need to use Exposure Compensation of +1 - +2 depending upon conditions.


You also can't create detail where it doesn't exist. If the lighting is such that the planes look dull and featureless to your eye, the camera isn't going to do any better.


Jets up high won't require as much shutter speed as jets down low. Jets up high will always be a challenge because you have to deal with atmospheric haze (pollution)