if you feel comfortable enough. As chad said youprobably want to expose for the planes, dont sweat the sky
Set your camera to M, spot or partial meter a plane’s fuselage thats A)parked on the ground and in the direction you’ll be shooting..hopefully its frontlit and B) grey or close to it
Reason being.
In that manner your exposure value is locked in (M) as opposed to any of the auto/semi auto modes.
In the semi modes (Av or Tv) either your f/stop is fixed (camera adjust SS on the fly) or your SS is fixed (camera adjust f/stop on the fly). While planes are fairly big (dependant on distance to it) unless your fairly practised at tracking flying subjects theres a good chance (probable) your center focus area will “slip” off target as you swing the lens about.
This can cause your cameras metering (and hence your exposure values) to be heavily swayed by the sky as it adjust your exposure value. So one split second your frame is 60% grey plane and 40% bright sky and the next its 30% (or less) plane and the balance bright sky.
The inverse of what you want.
In short your skies nicely exposed, but the plane depending on just how bright that sky is, is underexposed.
To test this.
Set your camera to Av (or TV) and partial metering.
Point it at a car, take your pic, it will be pretty much wht you want. Then swing the lens uptowards the sky. Watch what happens to your SS (if your in av). The light hasnt changed at all, but your SS due to the bright sky has just been gutted. That car if its in the frame will be underexposed.