It seems incredibly difficult to self-teach takeoff performance! I have
many times so far. I'll try to clearly explain my troubles and hopefully somebody will be able to help me clear it up.
1) Does the climb gradient requirements under FAR 25 all refer to gross aircraft performance?
For example: under FAR 25.121(b)(1) it requires 2.4% climb gradient from gear retraction to 400' above the Departure End of the Runway (DER). Is that 2.4% gross or 2.4% net? According to this FAA document it appears that it is gross and the net is reduced by 0.8%, IAW FAR 25.115(b)(1), to a net gradient of 1.6%.
2) My understanding is that FAR 25 has
nothing to do with obstacle clearance and is
only specifying a minimum level of performance that is required. Is that correct?
3) Under FAR 121.189 it details the net takeoff flight path clearing obstacles vertically by 35', etc. Is it correct then that, for obstacle clearance requirements, the net takeoff flight path for the 2nd segment would only be required to be 1.6%, and that gradient would be required to clear the obstacles by 35'?
I had always been under the impression that gross performance is the actual aircraft performance; net performance is the gross performance reduced by 0.8%; and that the performance requirements (gradients/accel distances) published in the FARs were referring to net performance - meaning that you are actually required to have a minimum of 2.4% net climb gradient in the 2nd segment.
4) My understanding is that a WAT (weight, altitude, temperature) chart ensures compliance with all FAR 25 performance requirements for takeoff. It is based on the most restrictive standard under FAR 25. Is that correct?
Thanks!