Assertion: vertical separation | /r/HasProperty | set at 1,000 feet
Facets:
value: at above flight level
type: LOCATION
value: in 1958
type: TEMPORAL
Source sentences:
text: In 1958 the standard vertical separation of aircraft in controlled airspace was set at 1,000 feet from ground level or sea level to flight level 290, and at 2,000 feet above flight level 290.