What is depicted on Enroute High Altitude Charts (HI Charts)?

Enroute High Altitude Charts, commonly referred to as HI Charts, are specifically designed to provide navigational information for aircraft operating at altitudes of 18,000 feet above sea level (ASL) and higher. These charts are essential for pilots flying in controlled airspace and are primarily used for navigation under Instrument Flight Rules (IFR). They depict significant features such as jet routes, airways, navigational aids (NAVAIDs), and other critical information relevant to high-altitude operations.

The correct choice highlights that these charts cover airspace over Canada and the North Atlantic at high altitudes, which is crucial for transcontinental and oceanic flights where standard navigational practices are vital due to the complexity and diversity of the air traffic environment. By focusing specifically on airspace use above 18,000 feet, HI Charts provide pilots with the necessary tools to navigate safely and efficiently in regions where lower altitude charts and VFR information would be insufficient.