The IRS will apply the flight hours in an audit situation because there is a flight log that they like to use to determine business vs personal. They will not accept the number of flights just for the reason you stated in your question.
The percentage of business use will be the same percentage as bus hours to total hours. So as in the previous example the business use will be 20%. You can change this percentage annually.
as for your original 179 question - if business use drops below 50% there may be recapture depending on how long you have owned the airplane. I don't usually use 179 for this type of asset for that reason.