# Boeing 747 Autopilot Pitch Modes Logic (Path Integrator)

I am hoping this will be my final question(s) concerning the 747 autopilot, given that the roll modes are now complete and I am finally on to the pitch modes...

All information on how this autopilot functions is from the following document: https://ntrs.nasa.gov/api/citations/19730001300/downloads/19730001300.pdf

Okay, so: The Path Integrator. Integral gains are shown on page 567, and the block diagram showing the integrator implementation is on page 571.

I am struggling to understand just how the path integrator works. Based on the block diagram, I am led to believe that the integrator takes whatever output the pitch autopilot has calculated up to that point, multiplies it by the appropriate integral gain based on mode, integrates, then feeds this into the summing point with the originally calculated output. As an example:

The vertical speed mode proportioner gain is 0.09 degrees pitch command/ft per second of error. Assuming for example a 3 ft/sec error in vertical speed, the commanded pitch change would be 0.27 degrees. Is 0.27 the initial value that the integrator would begin working off of or am I misinterpreting the diagrams? The integral units shown on page 567 are simply listed as "integral/displacement" which seems to me it is integrating based on whatever displacement command the autopilot is currently giving.

Thanks!