TSA PreCheck is wonderful to have at a US airport— unless you cannot actually use it. Whether you can or cannot use it depends on what airline you are flying on.
To check whether your outgoing flight is going to let you take advantage of TSA Precheck, see if your airline is on this TSA list: TSA PreCheck® Participating Airlines | Transportation Security Administration. If your airline is not on the list, you will be unable to use the TSA PreCheck line.
Why would TSA PreCheck be related to the airline? Because on your ticket, they mark who is eligible for TSA PreCheck. Airlines often asks for your TSA pre-check number when you purchase your ticket. They use this information to decide whether to mark your ticket as eligible for PreCheck with a star.
Unfortunately, low-cost carrier from Iceland, Play Air, is not on the list.
