Sudden accelerometer value changes, and quad become rocket

ArduCopter Copter 3.6
1

Screenshot_10
Screenshot_10.jpg2605×943 158 KB

Here is the screenshot of log.
I was flying althold mode, and during the flight, I’ve changed to pos_control mode.
Then, suddenly, accelerometer reading is 60m/s^2 as shown in the graph.

What happened? Quad just become rocket, and max throttle was logged (see below)

Screenshot_11
Screenshot_11.jpg2624×930 127 KB

Anyone knows what the problem is??

2

Probably better if you attach the complete log and a little description of the vehicle.