I recently got a Global Entry card. However on my last trip I was turned away from the pre check without an explanation. Why ? What do I have to do in addition to use pre check when I travel? Thank you.
To get that, you need to provide your known traveler number (KTN) to an airline that participates in precheck at your airport. Your KTN is your PASSID that appears on the back of your Global Entry card. You'll need to enter that number when you make airline reservations. If you've already booked your tickets, there's usually a way to enter it by accessing your reservation online, or you can contact the airline for help. The airline's systems will send this number to TSA to confirm your Precheck eligibility and put the indicator on your boarding pass.
If it still doesn't show up, you can ask the TSA to look into it. You should ensure the name on your air reservation exactly matches the name on your Global Entry membership. Their FAQ has additional information about how to use Precheck that may be of use.