Good morning. You file a flight plan with ATC as your true air speed in knots. ATC radar indicates your ground speed in knots to compute separation and possible conflicting traffic
Been there too. Schedule Seattle-Tokyo 10:10...actual 11:30...GS-295k. Almost diverted to Missawa. Boeing 707-320
NO fun. Got stuck once at 290. rougher than h°°ll and had to backtrack/divert to ANC. Chief pilot said that I could have made it. I asked with how much fuel? 5,000#...I spit my coffee all over his desk laughing. Boeing 747-200
My best was in a 707-320, Tokyo to Seattle. Scheduled 8:30 actual 7:40. Top ground speed 724 knots or 833 mph. Wind 260° @ 260 knots. GS was over 700k for the first 4 hours.
Had to wait at the gate for customs and immigration to come to work.
When I was driving a DC10, wx and winds permitting,departing SEA I would do a half circle East of Mt St Helens after it exploded here in Washington State...then climb and head for LAX and SAN.