The information is published in the National Flight Data Digest. An interagency agreement which provides for the effective utilization of all available facilities in all types of search and rescue missions. H- High altitude. Certain operational requirements make it necessary to use some of these aids at greater service ranges than specified. Extended range is made possible through flight inspection determinations.
Some aids also have lesser service range due to location, terrain, frequency protection, etc.
Previously issued traffic is not in sight. It may be followed by the pilot's request for the controller to provide assistance in avoiding the traffic. They were unable to contact ATC on a particular frequency. The time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the American Air Almanac, converted to local time. The hours between the end of evening civil twilight and the beginning of morning civil twilight or such other period between sunset and sunrise as may be specified by the appropriate authority.