A test flight was a test by means of actual or attempted flight to see how a spacecraft performs under real conditions. (Star Trek: Enterprise set artwork)
In 2143, during the test flight of the NX-Alpha and NX-Beta, A.G. Robinson became the first Human to break the warp 2 barrier. (ENT: "First Flight")
In 2368, Doctor Ja'Dar conducted the first flight test of a space vehicle propelled by a Soliton wave. Although the test was initially successful in using the wave to achieve warp speed without warp drive, the wave's sudden instability caused subspace distortions and the test had to be aborted. (TNG: "New Ground")
In 2374, the lifeform known as Steth claimed he was flight testing a new ship equipped with coaxial warp drive. (VOY: "Vis à Vis")
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