Every airframe is different. Sometimes even the same model airframe can have different settings from one airplane to the next. So, it's important to know that any settings you see for PIDs are not the settings you should use for your plane. Rather, this section is about the process of how to arrive at those PID settings. The first step is to make sure your airplane flies right with no Pixhawk input whatsoever.
Maidening an aircraft just means taking it into the air for the first time. The big difference between maidening a Pixhawk airplane and any other RC aircraft is that you should never use the trim controls on your radio.
Trim controls on the radio are small buttons or sliders near the sticks that allow a user to adjust the control surfaces in real time for straight flight by offsetting the value (PWMs) of the sticks. The problem is that by offsetting the values of the sticks by using trim controls, the Pixhawk will not know when the sticks are centered...