Operation ICICLE New FAA Program Tackles Aircraft Icing

by Marilyn Pearson, FAA General Aviation and Commercial Division

Winter in the United States can produce some of the riskiest weather for aviation, including freezing rain, freezing drizzle, and sleet. But these dangerous weather conditions were ideal for the FAA’s In-Cloud ICing and Large-drop Experiment (ICICLE) campaign. ICICLE seeks to collect in-flight data in some of the most challenging North American icing conditions.

By improving weather tools and model forecasts, the FAA hopes to reduce aircraft icing-related accidents and fatalities.

ICICLE is part of the FAA’s Aviation Weather Research Program, whose research aims to minimize the impact of weather on aircraft in the National Airspace System (NAS). Through ICICLE, the FAA will support development of both terminal and national-scale icing products. Data collected from ICICLE will help develop and validate weather tools to identify icing conditions a pilot might encounter, both in terminal area and en route environments. By improving weather tools and model forecasts, the FAA hopes to reduce aircraft icing-related accidents and fatalities.

Two FAA projects administered the ICICLE campaign: the Inflight Icing program (that supports research for the en route domain), and the Terminal Area Icing Weather Information for NextGen (TAIWIN) research project (that supports development and testing of new capabilities for the terminal area domain). Stephanie DiVito, FAA lead for both TAIWIN and ICICLE, notes that “Identifying these complex icing environments and forecasting them can be difficult. But for those who need to stay out of icing or certain types of icing, knowing where it does and does not exist is critical to safe operations.”

Frosty Flying

From January through March 2019, the National Research Council of Canada (NRC), in collaboration with the FAA and Environment and Climate Change Canada (ECCC), flew a Convair-580 twin-engine research aircraft into forecasted icing conditions in and throughout Rockford, Illinois and neighboring states. Scientists and engineers from the ECCC, the NRC, the FAA, and the National Center for Atmospheric Research (NCAR), worked to collect extensive environmental measurements using multiple onboard instruments.

Some members of the ICICLE team after a flight in mid-February 2019.

Forecasters monitored the weather throughout the program, both for short and long term planning. On a typical flight day, at about midnight before the flight, the on-duty forecaster began an in-depth analysis of current and forecasted weather for the day. Partnering universities nearby often released weather balloons to further analyze the cloud structure. Then in the early morning hours, scientists and Convair-580 crew members began work on the flight planning. The research team used the forecasts to plan the timeline, flight route, and altitudes needed for the flight crew to capture the in-cloud and surrounding ice-prone conditions. The airplane was equipped with special instruments to measure the range of particle sizes and concentration of both droplets and ice crystals throughout the takeoff, en route, and landing phases of the flights. Onboard cloud and precipitation radars allowed the scientists to characterize clouds above, below, and ahead of the aircraft. Because the size and concentration of liquid drops and particles influence the impact of icing on an aircraft, measuring these fields was key. The flight program targeted a broad spectrum of icing conditions.

Ben Bernstein, ICICLE science lead and primary operations director, helped identify and forecast icing conditions and guide the aircraft into and out of these conditions. “This flight program targeted a broad spectrum of icing conditions, including supercooled large drops, and focused on challenging transitions in icing that are critical to providing essential icing information to the flying public,” Bernstein explained.

Upper left: Ice accretion on Convair cockpit window. Upper right: Runback icing on Convair wing during flight. Lower left: Convair side-window icing indicative of supercooled large droplet SLD environment. Lower right: Convair windshield iced up in flight.

To enhance safety and allow for sampling at low altitudes, ICICLE teams operated over relatively flat terrain. The crew flew profiles that allowed capture of the entire vertical structure, from near the surface to above cloud top. Missed approaches captured sub-cloud and near surface conditions. Although air traffic volume limited access to favorable icing conditions in close proximity to cities like Chicago, light traffic in most areas of the domain enabled valuable 24-hour sampling.

It Takes a Team

NCAR was a critical partner in the research. During ICICLE, NCAR’s expertise in terminal area and in-flight icing conditions supported daily forecasting of weather conditions, flight operations, and initial analyses of icing weather tools under evaluation. A team of forecasters monitored the weather outlook and provided guidance on the best areas to find icing conditions. NCAR staff also monitored real-time data from satellite, radar, and ground-based instrumentation to help direct the aircraft once it was in flight. Other scientists supporting the program came from organizations such as the National Oceanic and Atmospheric Administration Earth System Research Laboratory, NASA Langley Research Center, the Desert Research Institute, Meteo-France, the UK Met Office, Deutscher Wetterdienst (the German meteorological office), and universities including Valparaiso, Northern Illinois, Illinois-Urbana Champaign, and Iowa State.

“There’s been a lot of collaboration on this project, with everyone focused on our mission,” says DiVito. “ICICLE was a major success, and we have collected a remarkable dataset that will help us continue to meet the FAA’s mission of improving safety in the NAS.”

So what are the next steps for ICICLE? Although the team is still processing and analyzing the vast amount of data that was collected, the FAA expects to publish an ICICLE science and operations plan, along with a detailed scientific article describing the program, deployment, and data collected, sometime later this year. Be on the lookout in a future issue for more on this important program.

Convair in the snow.

Marilyn Pearson is an aviation safety inspector in the FAA’s General Aviation and Commercial Division.

This article was originally published in the March/April 2020 issue of FAA Safety Briefing magazine.
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