BOE001 Test Flight Jan 21?

Multiple loops at VERY low altitude (reporting 0 feet at some points!) off the coast of Port Angeles WA today after a short test flight at altitude, any idea what this flight is doing? Looked like they were preparing to ditch for a bit there.

Aircraft generally transmit pressure altitude. ATC have systems that correct for this.
The Density altitude at the time was -1,500ft. So 0ft Pressure Altitude would be 1,500ft AMSL.

Ok I’ll buy that but these loops from 1500 to 2500 ASL in a 777 seems like some risky flying…