Bicopter Flying Well But Need Help With MW 2.1

[TPM]

Ive built and made great progress with my bicopter, but ive run into problems with understanding certain features.

first ive read the ATXheli pdf and googled terms many times, but:
what does "TPA" do exactly?
I want the "ALT PID" feature to work, how do I use it?

my goal: make this bicopter capable of human pilot or autonomous pilot flight.

TY, im grateful for any help.

video:
[youtube] http://www.youtube.com/watch?v=9MyLcRR5 ... e=youtu.be [/youtube]

[TPM]

is another TX/RX channel needed for the alt PID?

[Peter]

Throttle Pid Adjustment: with high throttle, lower the pid.