3DR Y6, Frame 10, 2nd flight, and Crash

My intention was to run Autotune. I had actually run autotune with 3.1 with the original Y6 Frame default.
I made a successful first flight with Frame 10 changes. Today, my intention was to run autotune again. Took off in Stabilize, tended to drift back toward the rear black arm. I ran it forward, put it in Alt Hold, then flipped my Channel 7 switch. Never got to autotune, there was a change in the motor sound copter headed back to an area at our field where other pilots were. I couldn’t get control so I had to cut power to avoid heading any further towards people.
The copters back bottom (Motor 4) prop was completely off. Other props broken, probably from the upside landing. It seems to point to a prop coming off, though I did check its tightness prior to flight.
I have attached the log. Any insights would be appreciated.

Since I didn’t receive any suggestions, I thought I would offer a few of my own.

  1. Better pre-flight - build a pre-flight station to easily hold the copter right side up, check props etc, flip it over in the stand to more easily do the same for bottom props, etc.
  2. I did notice in the log the “throttle out” increasing before the crash, as I presume APM was trying to compensate for the lost prop (Back Bottom).
  3. I was in super-simple mode, and in the heat of the moment was still using forward stick even though the copter had drifted behind “home” position, which made it go away from home closer to people on the ground. Not realizing that, and for safety’s sake, I throttle back and accepted the crash results.
  4. Re-attached motors routing the wires through the side hole on each arm with a rubber grommet so wires didn’t get chafed or cut. Any future crashed should lessen the problem of snapping off wires where they go into the motors. Thanks to all in the DIY Drones Y6 Copter group for this suggestion.