Stormy weather - FAA's next-generation air transportation system

The FAA's next-generation air transportation system will comprise a suite of networked software tools and a new breed of ground-based radar system to predict the path of storms.

The US Federal Aviation Administration is contemplating a fundamental shift in how airline pilots will avoid convective weather when planning and flying trips in the next generation air transportation system (NextGen), due to come into operation around 2025.

The strategy involves creating a new suite of highly automated and networked weather-related software tools and deploying a new breed of ground-based radar system that together will be able to accurately determine the path of storms as a function of time.

By knowing the position of severe weather at a given time, pilots flying or planning a flight in the NextGen system will have the ability to select routes that are diversion-free in advance, or efficiently and safety divert around weather in mid-flight. The FAA plans to have these "probabilistic" forecasts, which will include a metric indicating the confidence in the prediction, as part of an online suite of weather tools accessible by all pilots.

This should lead to less intervention by the FAA during the planning and execution of a flight, a basic tenet of the NextGen architecture. "From a weather perspective, we're looking at coming up with probabilities of a storm being at a particular location at a certain time," says William Benner, FAA weather processors manager. "You'll have to manage how close you'll want to be to that storm."

Route planning

Benner says the weather-planning software, which will aggregate a wide variety of weather data from sources such as the National Weather Service, will likely choose to close off storm-saturated airspace for route-planning purposes when the probabilities that severe weather - including hail, lightning and thunderstorms - will intersect a route are higher than a critical number, perhaps 80%. For aircraft already in flight, notification in advance that a route is blocked by weather will arrive via datalink early enough for strategic decisions to be made. From a tactical standpoint, pilots will continue use weather radar as a tool to divert around meteorological obstacles if needs be.

Severe weather today is handled in a much more hands-on way. The FAA, major airlines, the military and key air traffic control facilities having teleconferences every two hours each day starting at 07:15 and ending at 21:15 or 23:15, says Dan Smiley, facility manager at the FAA's Air Traffic Control System Command Centre in Herndon, Virginia, the focal point for the meetings.

Officials there evaluate "predictive" weather data from Nexrad, a network of 158 WSR-88D weather radar systems around the USA, meteorological data from airline flight departments, FAA's terminal radar and Doppler wind shear systems at airports, and the output of the Collaborative Collective Forecast Product (CCFP), a weather graphic that shows the intensity, geographic coverage and confidence in the forecast, with an outlook period of two, four or six hours, says Smiley. Nexrad, deployed in the 1990s, is a Doppler radar that outputs a map showing patterns of precipitation.

Depending on what the group decides, the FAA can impose, via VHF radio communications, transcontinental rerouting, ground delays or ground stops in order to accommodate severe weather and keep certain airports from saturating with traffic (see sidebar). On a microscopic scale, airports or regions can also institute ground stops, or increase distances between landing aircraft, says Smiley.

Decision making

With more advanced radar and decision-support tools arriving in the hands of pilots from 2020, FAA officials believe that much of the collaborative decision-making process can be automated, with strategic choices eliminating less efficient tactical moves. "The key is to to really understand what's happening with the weather," says Benner. "We have to give them accurate data at a rate that lets them know more quickly when something changes quickly."

The deployment of a more powerful weather radar network will be crucial, with electronically steered multi-function phased array radar (MPAR) technology being the primary candidate.

MPAR technology, used on the US Navy's Aegis-class destroyers since in the mid-1980s, can scan or track storm cells simultaneously with multiple electronically steered beams, capturing details of how a storm develops and helping to create better models for how the cells move and grow, according to the FAA and others. Currently the USA depends largely on Nexrad's WSR-88D mechanically steered radars to perform that function. Nexrad uses a single beam that must be mechanically steered through its range of motion, a process that takes five or more minutes to complete, compared to less than one minute for the MPAR.

Homeland security

In addition to its meteorological function, MPAR also works as a primary surveillance radar able to simultaneously track multiple targets, and can potentially have a homeland security function of diagnosing wind fields for tracking chemical, biological and nuclear plumes.

Fuelling the MPAR fire too at the FAA is the potential for billions in cost savings. A study by the Massachusetts Institute of Technology determined that government agencies that own and operate the USA's 510 weather and primary aircraft surveillance, made up of seven different types of radars including the WSR-88D, could replace all 510 with just 334 MPARs, reducing "sustain and replace" costs by $2.4 billion over 20 years.

Operational tests of MPAR for weather are currently taking place at the National Weather Radar Testbed in Norman, Oklahoma, where officials are successfully using a 9.38cm (3.7in), single-faced, phased array radar antenna to study live storms. NWRT is part of the National Oceanic and Atmospheric Administration's National Severe Storms Laboratory (NSSL).

The FAA, admittedly in the very early stages in developing both the ground radar infrastructure and software tools for NextGen network enabled weather, plans to spend $4.9 million of its own money researching the MPAR alternative in 2009 in a co-operative project with the NSSL, the National Weather Service, the US Air Force and others. It also plans next year to spend $20 million developing the tools to begin making various weather products available over a network.

Source: Flight International