F-MANU
If this data is correct, then according to the ground speed this aircraft went from a cruise-climb at 287 kts to a descent (less horizontal speed, altitude reducing), and then finally to a ground speed of 358 kts, i.e. it had resumed horizontal travel.
An emergency descent, for whatever reason, maybe got too fast in the descent and/or then pulled out too late, almost made it, but hit the sea?
The left turn seen in the HDG data; possibly yaw caused by a No 1 engine failure?