I prefer quality over quantity when taking shots. I have stood next to guys that press and hold the shutter while it takes 20-30 shots on a single pass. UGH! Pick your shot and make it count! For airplanes, I shoot shutter priority and will adjust as necessary and as comfort allows. Shutter speed depends on focal length and whether or not your lens has any image stabilization. My 50-500mm does not have any image stabilization, and I never use a tripod or monopod when shooting airplanes. So I have to be steady. I will usually start the day with faster shutter speeds and slow it down as I get settled in. The general rule of thumb is 1/focal length for max shutter speed. But I have never been one to use the rules.
I highly discourage anyone using full auto. Your results will vary and while you will get some nice photos, if you are photographing prop planes, you will stop the props altogether on sunny days.
FG-1 Corsair shot full auto in 2006, before I knew better:
At 1/500th (shot at 500mm) I get some prop blur, but not a lot.
But at least there is a sense of motion and everything else is in focus. While prop blur is a good thing, everything else blurry is not what anyone wants. Once comfortable with your gear and your techniques, experiment with lower shutter speeds. I think it is better to get your technique and composition skills at higher shutter speeds first. Otherwise you are just learning to take out of focus shots.
Now, with that being said, prop blur getting a full prop arc is the nirvana for some photographers. It all depends on the effect you want. Here are some examples:
Helicopter at 1/80th at 500mm. Tail rotor, full arc. Top rotor, good blur.
To contrast, here is the same helo, same show at 1/500th at 500mm. Some blur, not much, but shows motion. However, look at the jet wash from the exhaust. The level of detail in the exhaust is not evident at lower shutter speeds.
Keep in mind that full prop arc only works when the prop disc can be seen, like when light is dancing off the prop. Otherwise, it may look like there is NO prop. I have done that.
Here is an example of prop disappearance, at a higher shutter speed. The prop is just barely visible.
It all depends on conditions and lightning. Here is a Super Tucano with some nice blur.
Same airplane, different lighting (same day, time of day different)
Nice light, good arc
Light later in the day, less arc, and less visibility on the prop.
Lastly, situational awareness is KEY! Not only will it keep you alive if shooting airplanes on a moving ramp, it will also help you time shots at the right moment. My son has totally picked up on this.
Putting together prop arc and situational awareness...