This is the most important step in buying a plane. If you do this correctly, you will probably be OK. If you do this incorrectly, you will probably be a cautionary tale.

The basic question you need to answer is how many people you usually want to take and how far you want to go. The key word there is usually. Let’s say your vision for plane ownership is flying the spouse and kids to fun day trips once a month or so, and flying them plus two brothers to a family reunion 800 miles away every other year. In this case, your mission is not flying 5 people 800 miles; it’s flying 3 people 200 miles.

Don’t limit your thoughts to the number of seats; you also care about payload. For instance, if you want to fly a family of 4 to a weeklong trip every quarter, you’ll need to consider how much baggage capacity they’ll demand.

Also, consider your destination plans; depending on where you plan to fly your mission definition might include good short field performance, strong climb performance.

Here’s what a typical mission might look like:

Spouse (150lbs), 2 children (180 lbs), and 50lbs baggage flying out to family cabin 600 miles away. Nearest airport to the cabin has 2000ft runway and requires a 900fpm climb; density altitude frequently ~4000ft.

Another possibility:

Myself (and sometimes a <200lbs friend) flying <100mi for a $100 burger.

Above all be honest with yourself and treat your mission as completely immutable. When considering your passengers, be realistic about who will and won’t want to come along; not everyone likes flying. And as you begin your search, resist the urge to rationalize changing or relaxing your mission. If you decided you need a useful load of 1000lbs, then that’s what you need even if a less capable plane catches your eye.