When booking a flight, your Global Entry number should be entered into the field labeled "Known Traveler Number" (KTN). This field is usually located in the "Passenger Information" or "Secure Flight Data" section of the booking process, alongside your name and date of birth. Entering this 9-digit number—which can be found on the back of your Global Entry card or in your Trusted Traveler Programs (TTP) dashboard—is essential because it is what triggers the "TSA PreCheck" indicator on your boarding pass for domestic flights and departures from the U.S. If you forget to enter it during the initial booking, you can almost always add it later through the "Manage Booking" section of the airline's website or app, or even at the check-in counter. To ensure a seamless experience in 2026, it is highly recommended to save your KTN to your frequent flyer profile; this way, the number is automatically applied to every reservation you make with that airline, ensuring you never miss out on expedited security and immigration benefits.