We've termed the TBAS "mysterious" (like its predecessor, the BAT) because, frankly, there isn't much information out there on what it's like or how to prepare. Because it's a heavily controlled test, people who've taken it can't talk about it. Thus, ALL of the information below is from publicly-available info - and most of it is reported verbatim from the AETC sources.
So what is it? It is a computer-based flight aptitude test designed to measure a pilot applicant's psychomotor (aka hand-eye coordination) skills and cognitive aptitude. The results from your TBAS are combined with your AFOQT pilot composite score and your experience (flight hours) to compute your PCSM. The PCSM (Pilot Candidate Selection Method) score is the only way you can "see" your TBAS results - you'll never receive an actual TBAS score.
The TBAS is given at many locations across the states, although it is not as readily accessible as other tests due to the special computer workstation requirement. Click here for a listing of TBAS locations. The test takes about an hour. There are nine subtests - see more details below. In the beginning you will be presented with detailed instructions on your computer screen - take the time to go through the instructions carefully; you are not subject to a time constraint when viewing the instructions. Some of the sub-tests are self-paced, others are timed.
While there's no such thing as a practice test, you can prepare by 1) reviewing all of the information on this page and 2) practicing general hand-eye coordination by playing computer games.
Even though you can now take the TBAS twice (or, presumably, one each, if you've taken the BAT but now need a TBAS score due to timing), you may be subject to deadline constraints -- you have to wait six months between tests, it may be difficult to schedule a test depending on how far you live from test locations, and you'll need to make sure the TBAS is scored in time for your board deadline. Therefore, you ought to plan on only taking it once and make the best out of it! Get a good night's sleep prior to the test, and don't let nerves psych you out. For ROTC cadets, they often offer the test during Field Training. If you live far from another testing site, this may be a good option for you -- however, if you expect Field Training to be draining for you, or that it might not be the right environment for you to perform your best on the TBAS - WAIT! Schedule the test for another time.
Make sure to bring a filled-out candidate worksheet with you to the test. Also bring a valid picture ID, your social security card, your transcript, and your logbook (if you have flying experience). You will be asked to enter the info from your candidate worksheet into the computer workstation before the test begins. GOOD LUCK!