Avigation easements are certainly a real thing. The fact that you have not directly dealt with one as a homeowner could be for a number of reasons.
1) A previous landowner could have granted an avigation easement, and if so such a burden on the land would exist in perpetuity as a separate property right. You might even see it in the exclusions of your title insurance policy.
2) Similarly, the airport and the land where your home is located could have been previously owned by the same entity, and when that entity subdivided your residential parcel off from the land that was, or became, the airport, an avigation easement may have been reserved over your land. Like #1, above, this may show up on your title insurance policy.
3) Your applicable state or local government may have "taken" an avigation easement at some point in the past through eminent domain. Again this may show up in your title insurance policy.
4) Your property may be located far enough from the applicable flight paths or from the airport that an avigation easement is not necessary because no aircraft flies directly over your land at a low enough altitude to affect private ownership of the land below.