I started ATP in February, coming into the program with a PPL and about 140 hours TT. I will be headed off to Vegas to complete my CFI ratings (CFI, CFII, MEI) in a week and should be totally done by the end of July. It's not as fast as the brochure, no matter how fast you are.
Like you, I'm in my mid-thirties doing a career-change. The following are my impressions about the program.
FIRSTLY:
You will not succeed at the program unless you make it your full time job, especially during the private and instrument phases. It is immersion training, and requires your availability seven days a week for flying, studying, sim, studying, thinking about and dreaming about aviation.
Pros:
The program is solid, most of the instructors I've worked with have been very competent and genuinely invested in their students' progress, often working a lot of unpaid extra hours to help out.
The fleet is well-maintained, and airworthiness issues are taken care of right away. Any delay in completing the program will not be due to airplane availability.
The curriculum is well-organized and ATP provides a mountain of study material and guides to help you succeed.
It is very fast compared to a mom-and-pop Part 61 op.
Cons:
It is expensive. I was able to self-finance. A lot of the guys who took out loans are looking at some pretty huge monthly payments when they finish their training (if they successfully complete the program). ATP made sense to me as it was comparable / cheaper than attaining all these ratings at a local flying club, but I live in the Bay Area where flying is considerably more expensive than most other places in the country. Do the math for your own situation. (add ~50% to whatever estimates you get from your local flight schools.)
They are a large (the largest?) flying school and as such have a plethora of restrictions on how/when you get to fly. These restrictions are all borne of an abundance of caution and institutional experience, but they can limit the different experiences you have that can help you grow as a pilot. For instance, ATP aircraft are not allowed to land on runways shorter than 4000'. That basically eliminates most of the runways you would visit for funsies as a pilot.
If you go the zero to hero route, the ONLY time you will be alone in the airplane from Private to CFII is for the 10 hours of solo time required for the Private Pilot checkride. The rest of the time you will be flying with an instructor or your crew cross country partner. Also, you don't get to pick your solo x-country routes. You do the same route three times, that you flew with your instructor three times before. They don't leave a lot to chance.
Pilots come out of the program with their MEI CFI CFII without ever truly been PIC. (I mean "truly" as in -- COMPLETELY RESPONSIBLE for the flight -- there's always someone there to back you up / offer an opinion / make sure you don't do something stupid). The first time they're actually seriously in command is when they take up their first ab initio student.
Things move fast. Checkrides are scheduled way before you're ready to take them, in the expectation that when the check ride rolls around you WILL be ready. Sometimes you are, sometimes you aren't.
Depending where you live, you might need to either commute to school or get housing locally.
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My recommendation is, at the very least, go log a few flights with an instructor at your local airport find out if aviation is something you want to dump your money and life into. Do not take the loan out and sign up for ATP with 0 hours in your logbook.
If I had to do it again, I would still do the program, based on my financial position and cost comparisons. If the training center wasn't an easy 25 minutes away; if I had to take a loan; if I lived somewhere where flying and flight instruction was cheaper, it probably wouldn't have made sense for me to do ATP.
Hope this helps.
Fix