SELECT "Date" FROM table_80139 WHERE "Mach" = '0.662'
What Date has a Mach of 0.662?
CREATE TABLE table_80139 (
    "Vehicle Flight #" text,
    "Date" text,
    "Pilot" text,
    "Mach" real,
    "Velocity (km/h)" real,
    "Altitude (meters)" real,
    "Duration" text
)