Assertion: aircraft's altitude | /r/ObjectUse | used by unpressurized aircraft
Facets:
value: due to high terrain
type: CAUSE
value: due to distance from radar facilities
type: CAUSE
Source sentences:
text: In the U.S. system, at higher altitudes, over 90% of the U.S. airspace is covered by radar and often by multiple radar systems; however, coverage may be inconsistent at lower altitudes used by unpressurized aircraft due to high terrain or distance from radar facilities.