For the most part, once the employee is inside of the employee parking area (an area that requires their airport/airline
ID to be presented in order to enter), they are considered to have been cleared to enter the airport's SIDA (as many airports consider the employee lot as part of the SIDA, even if the lot is not on the airport property). Cars don't get searched, the only thing they might look for is if they are smuggling someone into the lot who is not authorized. The only time at many airports that flight crews will have to go through security is if it is not their home airport. There's no telling how many airline employees that are travelling non-rev don't go throuh the security screening process at their home airport.
The newest
TSA SD reguarding SIDA badges is aimed more towards those who are employed by retail shops, concessionaires, and their contractors. Companies like HMS Host, Hudson News, Paradies, Anderson News, & The News Group are the ones that are affected by these new directives. Prior to 9/11, the employees that worked in the retail and food concessions did not have any sort of
ID at all. Now those that will just work the shops and not enter sterile areas have a non-SIDA badge, which looks a lot different from an airport's SIDA badge. At many airports, there are many different colored SIDA badges, with each color representing a different group involved in operations at an airport. Airline employees have one colored badge, gov't employees (
TSA, FAA, city/state/county airport authority employees) another, contractors (airline related) another, contractors (construction) yet another, and concessionaires another. Many of these badges have restrictions, like concessionaire badges usually do not allow escorting of non-badged personnel into sterile areas; airlines employees can't enter certain areas without permission (like the AOA), while others have full access to anywhere and everywhere in the SIDA.
The only way I could see all airline employees getting screened would be if they built a facility at airports just for screening employees. At somewhere like
ATL, it could be hard to do because there are so many airline employee parking lots (most of them offsite of the airport). You would have to do employee security screening away from the main screening area at most airports due to the number of employees that work there.