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.