Originally Posted by
sethMCOflyer
It’s just not guaranteed, no other way to describe it. You’ll get it 99% of the time but there’s a chance you don’t. It’s also why your BP has to say “Precheck” and you can’t flash a global entry card.
Global Entry is different as it’s about their system easily recognizing you and allowing you through a special lane.
PreCheck and Trusted Traveler (Global Entry being one of the means of becoming a Trusted Traveler) are separate things. PreCheck is an airline function and only the airline can provide PreCheck access and only to those who are Trusted Travelers (there have been a few exceptions to this). That's why your KTN has to be in the airline's reservation system for a traveler to have PreCheck benefits. Also, though rare now, not every airline flying to the USA participates in PreCheck.