We have tickets on AA for Dec. If we apply for TSA Precheck can it be added to those flights?

Once you get your approval and receive your Trusted Traveler Number, simply go AA.com and add the TT Number to your AA Profile. You'll be registered with the airline for all upcoming flights.

Note: Even if you have TSA PreCheck there is no guarantee you be granted it for any given flight as TSA sometimes randomly decides not to grant Pre-Check for undisclosed reasons. It doesn't happen often but it can occur from time to time. You'll know you have PreCheck for any given flight as the Pre-Check logo will appear on your boarding pass.

Oh my gosh! I didn't realize we might be denied it afterall. We used to get it all the time but it hasn't happened lately. We do not fly alot but thought it would be worth getting since the lines were terrible last time...second thoughts now.

Get global entry instead. It includes PSA precheck and when you are reentering the US from abroad you have special lines, far faster to get through and no need to fill out those blue immigration sand customs forms. Ours cost $100.00 for 5 years and some credit cards, Chase Reserve for one, waive that fee.

We have taken dozens of flights since we got Global Entry about 6 years ago (recently renewed) and we cannot recall once being denied pre-check although once they ask my wife, on a random basis, to go through the body scanner. But we still were in the faster pre-check line.

I would check with AA to make sure this is correct. If you add your Traveler Number to your profile, it will be added to any new booking made. If it is added to a profile after the reservation has been made, I would add it to the specific reservation itself (as well as the profile for future bookings).

You can definitely add a Pre-check or Global Entry number to a reservation after booking by adding it to your frequent flier profile. It doesn't have to be there at the time the reservation was made. For AA at least it carries over without any major issues. I've had more trouble with Delta, where my pre-check number isn't usually communicated correctly to the TSA, so I'm almost always denied. If that happens, you just stand in line at the check-in counter and have the number added manually. It takes time, but I've never ultimately been denied pre-check when I did this. Usually, denials are either technical or because the airline doesn't participate (many international airlines don't).

<<You can definitely add a Pre-check or Global Entry number to a reservation after booking by adding it to your frequent flier profile. >> An FF profile is different to a regular profile. You should follow the steps that the airline tells you for adding TSA info to an existing reservation.

AA
https://www.aa.com/i18n/travel-info/security/tsa-precheck.jsp

DL
https://www.delta.com/us/en/check-in...y/global-entry
This clearly explained,
<<Please provide this number when booking your flights or add it to the Basic Info section in your Delta profile. You can also add it to existing trips that you already booked in My Trips. >>
My Trips is not the profile, it is the existing reservation.
In general, info in the profile is added to new bookings. In general, a profle does not mean an existing booking will be updated, unless the airline tells you otherwise.Your problem with DL is nothing to do with it being incorrectly communicated to the TSA, that scenario does not exist.
In general, this is how it works
1. TSA info can be added at the time of reservation as part of the booking process OR
2. TSA info can be added in the profile before the booking is made
3, TSA info can be added to existing reservation usually by adding it thru Manage my booking/trip etc ie directly to the booking

When I booked our last flight, AA asked for our TSA number even though it was supposed to be stored in my account.