Highways in the Sky


On cool and clear afternoons in the San Francisco Bay Area, I often see jet contrails going north to south. I imagine passengers jets from East Asia or cargo jets from Anchorage, Alaska flying to Los Angeles (LAX). While it would be logical to assume these lines trace straight line paths between airports, aircraft fly slightly crooked paths through a series of predetermined way points. These airways are analogous to a highway system crossing the continent by linking major cities along the way.

Like the U.S. Interstate Highway System, air traffic control systems are based on 50-year old technologies, in the case of air traffic control, ground-based radars and voice communications over radio.

Ground-based radar antennas rotate 5 or 12 times per minute “pinging” aircraft every 12 seconds (or 5 seconds near airports). It is thus possible for aircraft to be miles away from where the controllers think they are. As a consequence, aircraft must be spaced 3-5 miles apart (horizontally).

Air traffic communications have not kept up with digital communications technology. Controllers still issue mundane commands like, “Descend to five thousand (feet),” “Fly heading 270 (fly due west),” and “Reduce speed to 180 (knots).” Furthermore, pilots rely on air traffic controllers to advise them of nearby aircraft.

Meanwhile, higher fuel expenses are motivating the aerospace industry and airlines to experiment with new technologies and procedures because more efficient flying means lower fuel burn, and fuel is the biggest or second largest expense for airlines.

In the United States, a large air cargo carrier uses Automatic Dependent Surveillance-Broadcast (ADS-B) to exchange GPS data with other aircraft in their fleet. Pilots can track the position and direction of similarly equipped aircraft, just like a marine radar on any passenger ship. This is especially useful every night when about one hundred aircraft converge on their hub airport in a narrow time window. Without the positional awareness made possible by ADS-B, disruptions, such as storms, cause traffic jams in the air, forcing them to fly in circles while waiting for their turn to land. With ADS-B units in the cockpit, pilots can space themselves prior to arrival, thus reducing congestion at the hub airport and saving fuel.

Over the Pacific Ocean, the ASPIRE (Asia Pacific Initiative to Reduce Emissions) is testing operational optimizations to burn less fuel on transpacific flights. ASPIRE flights are allowed to take advantage of every optimization during their oceanic flights, most importantly greater freedom to change their altitude and heading based on actually encountered atmospheric conditions, as opposed to conditions forecast hours before flight. This is enabled by precision navigation (GPS) and better air-ground communications. On a recent ASPIRE flight, a 747 flying from LAX to Singapore, via Narita, Japan burned 10,868 kg less fuel, while emitting 33,769 kg less CO2 (carbon dioxide).

Unmanned aerial vehicles (UAV) present new challenges to air traffic management (ATM). In Europe, the ATLANTIDA initiative (Application of Leading Technologies to Unmanned Aerial Vehicles for Research and Development in ATM) is tackling the challenge of applying Trajectory-Based Operations (TBO) to air traffic management (ATM) for Unmanned Aerial Vehicles (UAV). Instead of human air traffic controllers proactively controlling aircraft movements, which is especially challenging with unmanned vehicles, TBO takes aircraft trajectory data and computes optimal solutions and presents decisions to the air traffic controller. ATLANTIDA uses a net-centric service-oriented architecture along with a novel trajectory definition technology called Aircraft Intent Description Language (AIDL) to capture and distribute trajectory data, and has selected RTI Data Distribution Service for its implementation.

The benefits of better air traffic control and management are more efficient flying and lower fuel burn. Consequently emissions are lower. RTI is playing a role in the future of air traffic management and helping the world be a little greener.

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